11 files changed, 1986 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..e4a677d
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,42 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(isogfx)
+
+set(CMAKE_C_STANDARD 17)
+set(CMAKE_C_STANDARD_REQUIRED On)
+set(CMAKE_C_EXTENSIONS Off)
+
+# isogfx
+
+add_library(isogfx
+  src/isogfx.c)
+
+target_include_directories(isogfx PUBLIC
+  include)
+
+target_link_libraries(isogfx PUBLIC
+  filesystem
+  mem
+  mempool)
+
+target_compile_options(isogfx PRIVATE -Wall -Wextra -Wpedantic)
+
+# Backend
+
+add_library(isogfx-backend
+  src/backend.c)
+
+target_include_directories(isogfx-backend PUBLIC
+  include)
+
+target_link_libraries(isogfx-backend PUBLIC
+  isogfx)
+
+target_link_libraries(isogfx-backend PRIVATE
+  gfx)
+
+target_compile_options(isogfx-backend PRIVATE -Wall -Wextra -Wpedantic)
+
+# Demos
+
+add_subdirectory(demos)
diff --git a/demos/CMakeLists.txt b/demos/CMakeLists.txt
new file mode 100644
index 0000000..c0a4101
--- /dev/null
+++ b/demos/CMakeLists.txt
@@ -0,0 +1,2 @@
+add_subdirectory(checkerboard)
+add_subdirectory(isomap)
diff --git a/demos/checkerboard/CMakeLists.txt b/demos/checkerboard/CMakeLists.txt
new file mode 100644
index 0000000..d1691c6
--- /dev/null
+++ b/demos/checkerboard/CMakeLists.txt
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(checkerboard)
+
+set(CMAKE_C_STANDARD 17)
+set(CMAKE_C_STANDARD_REQUIRED On)
+set(CMAKE_C_EXTENSIONS Off)
+
+add_executable(checkerboard
+  checkerboard.c)
+
+target_link_libraries(checkerboard PRIVATE
+  gfx-app
+  isogfx-backend)
+
+target_compile_options(checkerboard PRIVATE -Wall -Wextra -Wpedantic)
diff --git a/demos/checkerboard/checkerboard.c b/demos/checkerboard/checkerboard.c
new file mode 100644
index 0000000..dbc817c
--- /dev/null
+++ b/demos/checkerboard/checkerboard.c
@@ -0,0 +1,166 @@
+#include <isogfx/backend.h>
+#include <isogfx/isogfx.h>
+
+#include <gfx/app.h>
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+static const int WINDOW_WIDTH  = 1408;
+static const int WINDOW_HEIGHT = 960;
+static const int MAX_FPS       = 60;
+
+// Virtual screen dimensions.
+static const int SCREEN_WIDTH  = 704;
+static const int SCREEN_HEIGHT = 480;
+
+static const int TILE_WIDTH   = 32;
+static const int TILE_HEIGHT  = TILE_WIDTH / 2;
+static const int WORLD_WIDTH  = 20;
+static const int WORLD_HEIGHT = 20;
+
+static const TileDesc tile_set[] = {
+    {.type   = TileFromColour,
+     .width  = TILE_WIDTH,
+     .height = TILE_HEIGHT,
+     .colour = (Pixel){.r = 0x38, .g = 0x3b, .b = 0x46, .a = 0xff}},
+    {.type   = TileFromColour,
+     .width  = TILE_WIDTH,
+     .height = TILE_HEIGHT,
+     .colour = (Pixel){.r = 0xA5, .g = 0xb3, .b = 0xc0, .a = 0xff}},
+    {.type   = TileFromColour,
+     .width  = TILE_WIDTH,
+     .height = TILE_HEIGHT,
+     .colour = (Pixel){.r = 0xdc, .g = 0x76, .b = 0x84, .a = 0xff}},
+};
+
+typedef enum Colour {
+  Black,
+  White,
+  Red,
+} Colour;
+
+typedef struct GfxAppState {
+  IsoBackend* backend;
+  IsoGfx*     iso;
+  Tile        red;
+  int         xpick;
+  int         ypick;
+} GfxAppState;
+
+static void make_checkerboard(IsoGfx* iso, Tile black, Tile white) {
+  assert(iso);
+  for (int y = 0; y < isogfx_world_height(iso); ++y) {
+    for (int x = 0; x < isogfx_world_width(iso); ++x) {
+      const int  odd_col = x & 1;
+      const int  odd_row = y & 1;
+      const Tile value   = (odd_row ^ odd_col) == 0 ? black : white;
+      isogfx_set_tile(iso, x, y, value);
+    }
+  }
+}
+
+static bool init(GfxAppState* state, int argc, const char** argv) {
+  assert(state);
+
+  (void)argc;
+  (void)argv;
+
+  if (!(state->iso = isogfx_new(&(IsoGfxDesc){
+            .screen_width = SCREEN_WIDTH, .screen_height = SCREEN_HEIGHT}))) {
+    return false;
+  }
+  IsoGfx* iso = state->iso;
+
+  isogfx_resize(iso, SCREEN_WIDTH, SCREEN_HEIGHT);
+
+  if (!isogfx_make_world(
+          iso, &(WorldDesc){
+                   .tile_width   = TILE_WIDTH,
+                   .tile_height  = TILE_HEIGHT,
+                   .world_width  = WORLD_WIDTH,
+                   .world_height = WORLD_HEIGHT})) {
+    return false;
+  }
+
+  const Tile black = isogfx_make_tile(iso, &tile_set[Black]);
+  const Tile white = isogfx_make_tile(iso, &tile_set[White]);
+  state->red       = isogfx_make_tile(iso, &tile_set[Red]);
+  make_checkerboard(iso, black, white);
+
+  if (!(state->backend = IsoBackendInit(iso))) {
+    return false;
+  }
+
+  return true;
+}
+
+static void shutdown(GfxAppState* state) {
+  assert(state);
+
+  IsoBackendShutdown(&state->backend);
+  isogfx_del(&state->iso);
+}
+
+static void update(GfxAppState* state, double t, double dt) {
+  assert(state);
+  (void)dt;
+
+  IsoGfx* iso = state->iso;
+
+  isogfx_update(iso, t);
+
+  // Get mouse position in window coordinates.
+  double mouse_x, mouse_y;
+  gfx_app_get_mouse_position(&mouse_x, &mouse_y);
+
+  // Map from window coordinates to virtual screen coordinates.
+  IsoBackendGetMousePosition(
+      state->backend, mouse_x, mouse_y, &mouse_x, &mouse_y);
+
+  isogfx_pick_tile(iso, mouse_x, mouse_y, &state->xpick, &state->ypick);
+
+  printf("Picked tile: (%d, %d)\n", state->xpick, state->ypick);
+}
+
+static void render(GfxAppState* state) {
+  assert(state);
+
+  IsoGfx* iso = state->iso;
+
+  isogfx_render(iso);
+
+  if ((state->xpick != -1) && (state->ypick != -1)) {
+    isogfx_draw_tile(iso, state->xpick, state->ypick, state->red);
+  }
+
+  IsoBackendRender(state->backend, iso);
+}
+
+static void resize(GfxAppState* state, int width, int height) {
+  assert(state);
+
+  IsoBackendResizeWindow(state->backend, state->iso, width, height);
+}
+
+int main(int argc, const char** argv) {
+  GfxAppState state = {0};
+  gfx_app_run(
+      &(GfxAppDesc){
+          .argc              = argc,
+          .argv              = argv,
+          .width             = WINDOW_WIDTH,
+          .height            = WINDOW_HEIGHT,
+          .max_fps           = MAX_FPS,
+          .update_delta_time = MAX_FPS > 0 ? 1.0 / (double)MAX_FPS : 0.0,
+          .title             = "Isometric Renderer",
+          .app_state         = &state},
+      &(GfxAppCallbacks){
+          .init     = init,
+          .update   = update,
+          .render   = render,
+          .resize   = resize,
+          .shutdown = shutdown});
+  return 0;
+}
diff --git a/demos/isomap/CMakeLists.txt b/demos/isomap/CMakeLists.txt
new file mode 100644
index 0000000..2dbfd32
--- /dev/null
+++ b/demos/isomap/CMakeLists.txt
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(isomap)
+
+set(CMAKE_C_STANDARD 17)
+set(CMAKE_C_STANDARD_REQUIRED On)
+set(CMAKE_C_EXTENSIONS Off)
+
+add_executable(isomap
+  isomap.c)
+
+target_link_libraries(isomap PRIVATE
+  gfx-app
+  isogfx-backend)
+
+target_compile_options(isomap PRIVATE -Wall -Wextra -Wpedantic)
diff --git a/demos/isomap/isomap.c b/demos/isomap/isomap.c
new file mode 100644
index 0000000..a233659
--- /dev/null
+++ b/demos/isomap/isomap.c
@@ -0,0 +1,105 @@
+#include <isogfx/backend.h>
+#include <isogfx/isogfx.h>
+
+#include <gfx/app.h>
+
+#include <assert.h>
+#include <stdbool.h>
+
+static const int WINDOW_WIDTH  = 1408;
+static const int WINDOW_HEIGHT = 960;
+static const int MAX_FPS       = 60;
+
+// Virtual screen dimensions.
+static const int SCREEN_WIDTH  = 704;
+static const int SCREEN_HEIGHT = 480;
+
+typedef struct GfxAppState {
+  IsoBackend* backend;
+  IsoGfx*     iso;
+  int         xpick;
+  int         ypick;
+  SpriteSheet stag_sheet;
+  Sprite      stag;
+} GfxAppState;
+
+static bool init(GfxAppState* state, int argc, const char** argv) {
+  assert(state);
+  (void)argc;
+  (void)argv;
+
+  if (!(state->iso = isogfx_new(&(IsoGfxDesc){
+            .screen_width = SCREEN_WIDTH, .screen_height = SCREEN_HEIGHT}))) {
+    return false;
+  }
+  IsoGfx* iso = state->iso;
+
+  isogfx_resize(iso, SCREEN_WIDTH, SCREEN_HEIGHT);
+
+  if (!isogfx_load_world(iso, "/home/jeanne/assets/tilemaps/demo1.tm")) {
+    return false;
+  }
+
+  if (!isogfx_load_sprite_sheet(
+          iso, "/home/jeanne/assets/tilesets/scrabling/critters/stag/stag.ss",
+          &state->stag_sheet)) {
+    return false;
+  }
+
+  state->stag = isogfx_make_sprite(iso, state->stag_sheet);
+  isogfx_set_sprite_position(iso, state->stag, 5, 4);
+
+  if (!(state->backend = IsoBackendInit(iso))) {
+    return false;
+  }
+
+  return true;
+}
+
+static void shutdown(GfxAppState* state) {
+  assert(state);
+  //
+}
+
+static void update(GfxAppState* state, double t, double dt) {
+  assert(state);
+  (void)dt;
+
+  IsoGfx* iso = state->iso;
+  isogfx_update(iso, t);
+}
+
+static void render(GfxAppState* state) {
+  assert(state);
+
+  IsoGfx* iso = state->iso;
+  isogfx_render(iso);
+  IsoBackendRender(state->backend, iso);
+}
+
+static void resize(GfxAppState* state, int width, int height) {
+  assert(state);
+
+  IsoBackendResizeWindow(state->backend, state->iso, width, height);
+}
+
+int main(int argc, const char** argv) {
+  GfxAppState state = {0};
+  gfx_app_run(
+      &(GfxAppDesc){
+          .argc              = argc,
+          .argv              = argv,
+          .width             = WINDOW_WIDTH,
+          .height            = WINDOW_HEIGHT,
+          .max_fps           = MAX_FPS,
+          .update_delta_time = MAX_FPS > 0 ? 1.0 / (double)MAX_FPS : 0.0,
+          .title             = "Isometric Renderer",
+          .app_state         = &state},
+      &(GfxAppCallbacks){
+          .init     = init,
+          .update   = update,
+          .render   = render,
+          .resize   = resize,
+          .shutdown = shutdown});
+  return 0;
+}
diff --git a/include/isogfx/backend.h b/include/isogfx/backend.h
new file mode 100644
index 0000000..172991d
--- /dev/null
+++ b/include/isogfx/backend.h
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <stdbool.h>
+
+typedef struct Gfx    Gfx;
+typedef struct IsoGfx IsoGfx;
+
+typedef struct IsoBackend IsoBackend;
+
+/// Initialize the backend.
+IsoBackend* IsoBackendInit(const IsoGfx*);
+
+/// Shut down the backend.
+void IsoBackendShutdown(IsoBackend**);
+
+/// Notify the backend of a window resize event.
+/// This allows the backend to determine how to position and scale the iso
+/// screen buffer on the graphics window.
+void IsoBackendResizeWindow(IsoBackend*, const IsoGfx*, int width, int height);
+
+/// Render the iso screen to the graphics window.
+void IsoBackendRender(const IsoBackend*, const IsoGfx*);
+
+/// Map window coordinates to iso space coordinates.
+/// This takes into account any possible resizing done by the backend in
+/// response to calls to IsoBackendResizeWindow().
+bool IsoBackendGetMousePosition(
+    const IsoBackend*, double window_x, double window_y, double* x, double* y);
diff --git a/include/isogfx/isogfx.h b/include/isogfx/isogfx.h
new file mode 100644
index 0000000..3421a7b
--- /dev/null
+++ b/include/isogfx/isogfx.h
@@ -0,0 +1,136 @@
+/*
+ * Isometric rendering engine.
+ */
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+typedef struct IsoGfx IsoGfx;
+
+/// Sprite sheet handle.
+typedef uint16_t SpriteSheet;
+
+/// Sprite handle.
+typedef uint16_t Sprite;
+
+/// Tile handle.
+typedef uint16_t Tile;
+
+/// Colour channel.
+typedef uint8_t Channel;
+
+typedef struct Pixel {
+  Channel r, g, b, a;
+} Pixel;
+
+typedef enum TileDescType {
+  TileFromColour,
+  TileFromFile,
+  TileFromMemory,
+} TileDescType;
+
+typedef struct TileDesc {
+  TileDescType type;
+  int          width;  /// Tile width in pixels.
+  int          height; /// Tile height in pixels.
+  union {
+    Pixel colour; /// Constant colour tile.
+    struct {
+      const char* path;
+    } file;
+    struct {
+      const uint8_t* data; /// sizeof(Pixel) * width * height
+    } mem;
+  };
+} TileDesc;
+
+typedef struct WorldDesc {
+  int tile_width;    /// Base tile width in pixels.
+  int tile_height;   /// Base tile height in pixels.
+  int world_width;   /// World width in tiles.
+  int world_height;  /// World height in tiles.
+  int max_num_tiles; /// 0 for an implementation-defined default.
+} WorldDesc;
+
+typedef struct IsoGfxDesc {
+  int screen_width;                 /// Screen width in pixels.
+  int screen_height;                /// Screen height in pixels.
+  int max_num_sprites;              /// 0 for an implementation-defined default.
+  int sprite_sheet_pool_size_bytes; /// 0 for an implementation-defined default.
+} IsoGfxDesc;
+
+/// Create a new isometric graphics engine.
+IsoGfx* isogfx_new(const IsoGfxDesc*);
+
+/// Destroy the isometric graphics engine.
+void isogfx_del(IsoGfx**);
+
+/// Create an empty world.
+bool isogfx_make_world(IsoGfx*, const WorldDesc*);
+
+/// Load a world from a tile map (.TM) file.
+bool isogfx_load_world(IsoGfx*, const char* filepath);
+
+/// Return the world's width.
+int isogfx_world_width(const IsoGfx*);
+
+/// Return the world's height.
+int isogfx_world_height(const IsoGfx*);
+
+/// Create a new tile.
+Tile isogfx_make_tile(IsoGfx*, const TileDesc*);
+
+/// Set the tile at position (x,y).
+void isogfx_set_tile(IsoGfx*, int x, int y, Tile);
+
+/// Set the tiles in positions in the range (x0,y0) - (x1,y1).
+void isogfx_set_tiles(IsoGfx*, int x0, int y0, int x1, int y1, Tile);
+
+/// Load a sprite sheet (.SS) file.
+bool isogfx_load_sprite_sheet(IsoGfx*, const char* filepath, SpriteSheet*);
+
+/// Create an animated sprite.
+Sprite isogfx_make_sprite(IsoGfx*, SpriteSheet);
+
+/// Destroy the sprite.
+void isogfx_del_sprite(IsoGfx*, Sprite);
+
+/// Destroy all the sprites.
+void isogfx_del_sprites(IsoGfx*);
+
+/// Set the sprite's position.
+void isogfx_set_sprite_position(IsoGfx*, Sprite, int x, int y);
+
+/// Set the sprite's current animation.
+void isogfx_set_sprite_animation(IsoGfx*, Sprite, int animation);
+
+/// Update the renderer.
+///
+/// Currently this updates the sprite animations.
+void isogfx_update(IsoGfx*, double t);
+
+/// Render the world.
+void isogfx_render(IsoGfx*);
+
+/// Draw/overlay a tile at position (x,y).
+///
+/// This function just renders a tile at position (x,y) and should be called
+/// after isogfx_render() to obtain the correct result. To set the tile at
+/// position (x,y) instead, use isogfx_set_tile().
+void isogfx_draw_tile(IsoGfx*, int x, int y, Tile);
+
+/// Resize the virtual screen's dimensions.
+bool isogfx_resize(IsoGfx*, int screen_width, int screen_height);
+
+/// Get the virtual screen's dimensions.
+void isogfx_get_screen_size(const IsoGfx*, int* width, int* height);
+
+/// Return a pointer to the virtual screen's colour buffer.
+///
+/// Call after each call to isogfx_render() to retrieve the render output.
+const Pixel* isogfx_get_screen_buffer(const IsoGfx*);
+
+/// Translate Cartesian to isometric coordinates.
+void isogfx_pick_tile(
+    const IsoGfx*, double xcart, double ycart, int* xiso, int* yiso);
diff --git a/src/backend.c b/src/backend.c
new file mode 100644
index 0000000..db91647
--- /dev/null
+++ b/src/backend.c
@@ -0,0 +1,199 @@
+#include <isogfx/backend.h>
+#include <isogfx/isogfx.h>
+
+#include <gfx/core.h>
+#include <gfx/gfx.h>
+#include <gfx/renderer.h>
+#include <gfx/scene.h>
+#include <gfx/util/geometry.h>
+#include <gfx/util/shader.h>
+
+#include <assert.h>
+#include <stdlib.h>
+
+typedef struct IsoBackend {
+  Gfx*   gfx;
+  Scene* scene;
+  /// The screen or "iso screen" refers to the colour buffer of the iso graphics
+  /// library. This texture is used to draw the iso screen onto the graphics
+  /// window.
+  Texture* screen_texture;
+  /// Window size.
+  int window_width;
+  int window_height;
+  /// The viewport refers to the area inside the window to which screen_texture
+  /// is drawn. It is a scaled version of the iso screen, scaled while
+  /// respecting the iso screen's aspect ratio to prevent distortion.
+  int    viewport_x, viewport_y, viewport_width, viewport_height;
+  double stretch; // Stretch factor from iso screen dimensions to viewport
+                  // dimensions.
+} IsoBackend;
+
+IsoBackend* IsoBackendInit(const IsoGfx* iso) {
+  assert(iso);
+
+  IsoBackend* backend = calloc(1, sizeof(IsoBackend));
+  if (!backend) {
+    return 0;
+  }
+
+  if (!(backend->gfx = gfx_init())) {
+    goto cleanup;
+  }
+  GfxCore* gfxcore = gfx_get_core(backend->gfx);
+
+  int screen_width, screen_height;
+  isogfx_get_screen_size(iso, &screen_width, &screen_height);
+
+  if (!(backend->screen_texture = gfx_make_texture(
+            gfxcore, &(TextureDesc){
+                         .width     = screen_width,
+                         .height    = screen_height,
+                         .dimension = Texture2D,
+                         .format    = TextureSRGBA8,
+                         .filtering = NearestFiltering,
+                         .wrap      = ClampToEdge,
+                         .mipmaps   = false}))) {
+    goto cleanup;
+  }
+
+  ShaderProgram* shader = gfx_make_view_texture_shader(gfxcore);
+  if (!shader) {
+    goto cleanup;
+  }
+
+  Geometry* geometry = gfx_make_quad_11(gfxcore);
+  if (!geometry) {
+    goto cleanup;
+  }
+
+  MaterialDesc material_desc = (MaterialDesc){.num_uniforms = 1};
+  material_desc.uniforms[0]  = (ShaderUniform){
+       .type          = UniformTexture,
+       .value.texture = backend->screen_texture,
+       .name          = sstring_make("Texture")};
+  Material* material = gfx_make_material(&material_desc);
+  if (!material) {
+    return false;
+  }
+
+  const MeshDesc mesh_desc =
+      (MeshDesc){.geometry = geometry, .material = material, .shader = shader};
+  Mesh* mesh = gfx_make_mesh(&mesh_desc);
+  if (!mesh) {
+    goto cleanup;
+  }
+
+  SceneObject* object =
+      gfx_make_object(&(ObjectDesc){.num_meshes = 1, .meshes = {mesh}});
+  if (!object) {
+    goto cleanup;
+  }
+
+  backend->scene  = gfx_make_scene();
+  SceneNode* node = gfx_make_object_node(object);
+  SceneNode* root = gfx_get_scene_root(backend->scene);
+  gfx_set_node_parent(node, root);
+
+  return backend;
+
+cleanup:
+  if (backend->gfx) {
+    gfx_destroy(&backend->gfx);
+  }
+  free(backend);
+  return 0;
+}
+
+void IsoBackendShutdown(IsoBackend** ppApp) {
+  assert(ppApp);
+
+  IsoBackend* app = *ppApp;
+  if (!app) {
+    return;
+  }
+
+  gfx_destroy(&app->gfx);
+}
+
+void IsoBackendResizeWindow(
+    IsoBackend* app, const IsoGfx* iso, int width, int height) {
+  assert(app);
+  assert(iso);
+
+  app->window_width  = width;
+  app->window_height = height;
+
+  // Virtual screen dimensions.
+  int screen_width, screen_height;
+  isogfx_get_screen_size(iso, &screen_width, &screen_height);
+
+  // Stretch the virtual screen onto the viewport while respecting the screen's
+  // aspect ratio to prevent distortion.
+  if (width > height) { // Wide screen.
+    app->stretch         = (double)height / (double)screen_height;
+    app->viewport_width  = (int)((double)screen_width * app->stretch);
+    app->viewport_height = height;
+    app->viewport_x      = (width - app->viewport_width) / 2;
+    app->viewport_y      = 0;
+  } else { // Tall screen.
+    app->stretch         = (double)width / (double)screen_width;
+    app->viewport_width  = width;
+    app->viewport_height = (int)((float)screen_height * app->stretch);
+    app->viewport_x      = 0;
+    app->viewport_y      = (height - app->viewport_height) / 2;
+  }
+}
+
+void IsoBackendRender(const IsoBackend* app, const IsoGfx* iso) {
+  assert(app);
+  assert(iso);
+
+  const Pixel* screen = isogfx_get_screen_buffer(iso);
+  assert(screen);
+  gfx_update_texture(app->screen_texture, &(TextureDataDesc){.pixels = screen});
+
+  GfxCore*  gfxcore  = gfx_get_core(app->gfx);
+  Renderer* renderer = gfx_get_renderer(app->gfx);
+
+  // Clear the whole window.
+  gfx_set_viewport(gfxcore, 0, 0, app->window_width, app->window_height);
+  gfx_clear(gfxcore, vec4_make(0, 0, 0, 0));
+
+  // Draw to the subregion where the virtual screen can stretch without
+  // distortion.
+  gfx_set_viewport(
+      gfxcore, app->viewport_x, app->viewport_y, app->viewport_width,
+      app->viewport_height);
+
+  // Render the iso screen.
+  gfx_start_frame(gfxcore);
+  gfx_render_scene(
+      renderer, &(RenderSceneParams){
+                    .mode = RenderDefault, .scene = app->scene, .camera = 0});
+  gfx_end_frame(gfxcore);
+}
+
+bool IsoBackendGetMousePosition(
+    const IsoBackend* app, double window_x, double window_y, double* x,
+    double* y) {
+  assert(app);
+
+  // Translate from window coordinates to the subregion where the stretched
+  // iso screen is rendered.
+  const double screen_x = window_x - app->viewport_x;
+  const double screen_y = window_y - app->viewport_y;
+
+  // Position may be out of bounds.
+  if ((0 <= screen_x) && (screen_x < app->viewport_width) && (0 <= screen_y) &&
+      (screen_y < app->viewport_height)) {
+    // Scale back from the stretched subregion to the iso screen dimensions.
+    *x = screen_x / app->stretch;
+    *y = screen_y / app->stretch;
+    return true;
+  } else {
+    *x = -1;
+    *y = -1;
+    return false;
+  }
+}
diff --git a/src/isogfx.c b/src/isogfx.c
new file mode 100644
index 0000000..52c4ae2
--- /dev/null
+++ b/src/isogfx.c
@@ -0,0 +1,952 @@
+#include <isogfx/isogfx.h>
+
+#include <filesystem.h>
+#include <mem.h>
+#include <mempool.h>
+#include <path.h>
+
+#include <linux/limits.h>
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/// Maximum number of tiles unless the user specifies a value.
+#define DEFAULT_MAX_NUM_TILES 1024
+
+/// Maximum number of sprites unless the user specifies a value.
+#define DEFAULT_MAX_NUM_SPRITES 128
+
+/// Size of sprite sheet pool in bytes unless the user specifies a value.
+#define DEFAULT_SPRITE_SHEET_POOL_SIZE_BYTES (8 * 1024 * 1024)
+
+/// Default animation speed.
+#define ANIMATION_FPS 10
+
+/// Time between animation updates.
+#define ANIMATION_UPDATE_DELTA (1.0 / ANIMATION_FPS)
+
+typedef struct ivec2 {
+  int x, y;
+} ivec2;
+
+typedef struct vec2 {
+  double x, y;
+} vec2;
+
+// -----------------------------------------------------------------------------
+// Tile set (TS) and tile map (TM) file formats.
+// -----------------------------------------------------------------------------
+
+/// Maximum length of path strings in .TS and .TM files.
+#define MAX_PATH_LENGTH 128
+
+typedef struct Ts_Tile {
+  uint16_t width;     /// Tile width in pixels.
+  uint16_t height;    /// Tile height in pixels.
+  Pixel    pixels[1]; /// Count: width * height.
+} Ts_Tile;
+
+typedef struct Ts_TileSet {
+  uint16_t num_tiles;
+  uint16_t max_tile_width;  /// Maximum tile width in pixels.
+  uint16_t max_tile_height; /// Maximum tile height in pixels.
+  Ts_Tile  tiles[1];        /// Count: num_tiles.
+} Ts_TileSet;
+
+typedef struct Tm_Layer {
+  union {
+    char tileset_path[MAX_PATH_LENGTH]; // Relative to the Tm_Map file.
+  };
+  Tile tiles[1]; /// Count: world_width * world_height.
+} Tm_Layer;
+
+typedef struct Tm_Map {
+  uint16_t world_width;  /// World width in number of tiles.
+  uint16_t world_height; /// World height in number of tiles.
+  uint16_t base_tile_width;
+  uint16_t base_tile_height;
+  uint16_t num_layers;
+  Tm_Layer layers[1]; // Count: num_layers.
+} Tm_Map;
+
+static inline const Tm_Layer* tm_map_get_next_layer(
+    const Tm_Map* map, const Tm_Layer* layer) {
+  assert(map);
+  assert(layer);
+  return (const Tm_Layer*)((const uint8_t*)layer + sizeof(Tm_Layer) +
+                           ((map->world_width * map->world_height - 1) *
+                            sizeof(Tile)));
+}
+
+static inline const Ts_Tile* ts_tileset_get_next_tile(
+    const Ts_TileSet* tileset, const Ts_Tile* tile) {
+  assert(tileset);
+  assert(tile);
+  return (const Ts_Tile*)((const uint8_t*)tile + sizeof(Ts_Tile) +
+                          ((tile->width * tile->height - 1) * sizeof(Pixel)));
+}
+
+// -----------------------------------------------------------------------------
+// Sprite sheet file format.
+// -----------------------------------------------------------------------------
+
+/// A row of sprites in a sprite sheet.
+///
+/// Each row in a sprite sheet can have a different number of columns.
+///
+/// The pixels of the row follow a "sprite-major" order. It contains the
+/// 'sprite_width * sprite_height' pixels for the first column/sprite, then the
+/// second column/sprite, etc.
+///
+/// Pixels are 8-bit indices into the sprite sheet's colour palette.
+typedef struct Ss_Row {
+  uint16_t num_cols;  /// Number of columns in this row.
+  uint8_t  pixels[1]; /// Count: num_cols * sprite_width * sprite_height.
+} Ss_Row;
+
+typedef struct Ss_Palette {
+  uint16_t num_colours;
+  Pixel    colours[1]; /// Count: num_colors.
+} Ss_Palette;
+
+/// Sprite sheet top-level data definition.
+///
+/// Sprite width and height are assumed constant throughout the sprite sheet.
+typedef struct Ss_SpriteSheet {
+  uint16_t   sprite_width;  /// Sprite width in pixels.
+  uint16_t   sprite_height; /// Sprite height in pixels.
+  uint16_t   num_rows;
+  Ss_Palette palette; /// Variable size.
+  Ss_Row     rows[1]; /// Count: num_rows. Variable offset.
+} Ss_SpriteSheet;
+
+static inline const Ss_Row* get_sprite_sheet_row(
+    const Ss_SpriteSheet* sheet, int row) {
+  assert(sheet);
+  assert(row >= 0);
+  assert(row < sheet->num_rows);
+  // Skip over the palette.
+  const Ss_Row* rows =
+      (const Ss_Row*)(&sheet->palette.colours[0] + sheet->palette.num_colours);
+  return &rows[row];
+}
+
+static inline const uint8_t* get_sprite_sheet_sprite(
+    const Ss_SpriteSheet* sheet, const Ss_Row* row, int col) {
+  assert(sheet);
+  assert(row);
+  assert(col >= 0);
+  assert(col < row->num_cols);
+  const int sprite_offset = col * sheet->sprite_width * sheet->sprite_height;
+  const uint8_t* sprite   = &row->pixels[sprite_offset];
+  return sprite;
+}
+
+// -----------------------------------------------------------------------------
+// Renderer state.
+// -----------------------------------------------------------------------------
+
+typedef struct TileData {
+  uint16_t width;
+  uint16_t height;
+  uint16_t pixels_handle; // Handle to the tile's pixels in the pixel pool.
+} TileData;
+
+// File format is already convenient for working in memory.
+typedef Ss_Row         SpriteSheetRow;
+typedef Ss_SpriteSheet SpriteSheetData;
+
+typedef struct SpriteData {
+  SpriteSheet sheet; // Handle to the sprite's sheet.
+  ivec2       position;
+  int         animation; // Current animation.
+  int         frame;     // Current frame of animation.
+} SpriteData;
+
+DEF_MEMPOOL_DYN(TilePool, TileData)
+DEF_MEM_DYN(PixelPool, Pixel)
+
+DEF_MEMPOOL_DYN(SpritePool, SpriteData)
+DEF_MEM_DYN(SpriteSheetPool, SpriteSheetData)
+
+typedef struct IsoGfx {
+  int             screen_width;
+  int             screen_height;
+  int             tile_width;
+  int             tile_height;
+  int             world_width;
+  int             world_height;
+  int             max_num_sprites;
+  int             sprite_sheet_pool_size_bytes;
+  double          last_animation_time;
+  Tile*           world;
+  Pixel*          screen;
+  TilePool        tiles;
+  PixelPool       pixels;
+  SpritePool      sprites;
+  SpriteSheetPool sheets;
+} IsoGfx;
+
+// -----------------------------------------------------------------------------
+// Math and world / tile / screen access.
+// -----------------------------------------------------------------------------
+
+static inline ivec2 ivec2_add(ivec2 a, ivec2 b) {
+  return (ivec2){.x = a.x + b.x, .y = a.y + b.y};
+}
+
+static inline ivec2 ivec2_scale(ivec2 a, int s) {
+  return (ivec2){.x = a.x * s, .y = a.y * s};
+}
+
+static inline ivec2 iso2cart(ivec2 iso, int s, int t, int w) {
+  return (ivec2){
+      .x = (iso.x - iso.y) * (s / 2) + (w / 2), .y = (iso.x + iso.y) * (t / 2)};
+}
+
+// Method 1.
+// static inline vec2 cart2iso(vec2 cart, int s, int t, int w) {
+//  const double x    = cart.x - (double)(w / 2);
+//  const double xiso = (x * t + cart.y * s) / (double)(s * t);
+//  return (vec2){
+//      .x = (int)(xiso), .y = (int)((2.0 / (double)t) * cart.y - xiso)};
+//}
+
+// Method 2.
+static inline vec2 cart2iso(vec2 cart, int s, int t, int w) {
+  const double one_over_s = 1. / (double)s;
+  const double one_over_t = 1. / (double)t;
+  const double x          = cart.x - (double)(w / 2);
+  return (vec2){
+      .x = (one_over_s * x + one_over_t * cart.y),
+      .y = (-one_over_s * x + one_over_t * cart.y)};
+}
+
+static const Pixel* tile_xy_const_ref(
+    const IsoGfx* iso, const TileData* tile, int x, int y) {
+  assert(iso);
+  assert(tile);
+  assert(x >= 0);
+  assert(y >= 0);
+  assert(x < tile->width);
+  assert(y < tile->height);
+  return &mem_get_chunk(&iso->pixels, tile->pixels_handle)[y * tile->width + x];
+}
+
+// static Pixel tile_xy(const IsoGfx* iso, const TileData* tile, int x, int y) {
+//   return *tile_xy_const_ref(iso, tile, x, y);
+// }
+
+static Pixel* tile_xy_mut(const IsoGfx* iso, TileData* tile, int x, int y) {
+  return (Pixel*)tile_xy_const_ref(iso, tile, x, y);
+}
+
+static inline const Tile* world_xy_const_ref(const IsoGfx* iso, int x, int y) {
+  assert(iso);
+  assert(x >= 0);
+  assert(y >= 0);
+  assert(x < iso->world_width);
+  assert(y < iso->world_height);
+  return &iso->world[y * iso->world_width + x];
+}
+
+static inline Tile world_xy(const IsoGfx* iso, int x, int y) {
+  return *world_xy_const_ref(iso, x, y);
+}
+
+static inline Tile* world_xy_mut(IsoGfx* iso, int x, int y) {
+  return (Tile*)world_xy_const_ref(iso, x, y);
+}
+
+static inline const Pixel* screen_xy_const_ref(
+    const IsoGfx* iso, int x, int y) {
+  assert(iso);
+  assert(x >= 0);
+  assert(y >= 0);
+  assert(x < iso->screen_width);
+  assert(y < iso->screen_height);
+  return &iso->screen[y * iso->screen_width + x];
+}
+
+static inline Pixel screen_xy(IsoGfx* iso, int x, int y) {
+  return *screen_xy_const_ref(iso, x, y);
+}
+
+static inline Pixel* screen_xy_mut(IsoGfx* iso, int x, int y) {
+  return (Pixel*)screen_xy_const_ref(iso, x, y);
+}
+
+static int calc_num_tile_blocks(
+    int base_tile_width, int base_tile_height, int tile_width,
+    int tile_height) {
+  const int base_tile_size = base_tile_width * base_tile_height;
+  const int tile_size      = tile_width * tile_height;
+  const int num_blocks     = tile_size / base_tile_size;
+  return num_blocks;
+}
+
+// -----------------------------------------------------------------------------
+// Renderer, world and tile management.
+// -----------------------------------------------------------------------------
+
+IsoGfx* isogfx_new(const IsoGfxDesc* desc) {
+  assert(desc->screen_width > 0);
+  assert(desc->screen_height > 0);
+  // Part of our implementation assumes even widths and heights for precision.
+  assert((desc->screen_width & 1) == 0);
+  assert((desc->screen_height & 1) == 0);
+
+  IsoGfx* iso = calloc(1, sizeof(IsoGfx));
+  if (!iso) {
+    return 0;
+  }
+
+  iso->screen_width  = desc->screen_width;
+  iso->screen_height = desc->screen_height;
+
+  iso->last_animation_time = 0.0;
+
+  iso->max_num_sprites = desc->max_num_sprites == 0 ? DEFAULT_MAX_NUM_SPRITES
+                                                    : desc->max_num_sprites;
+  iso->sprite_sheet_pool_size_bytes = desc->sprite_sheet_pool_size_bytes == 0
+                                          ? DEFAULT_SPRITE_SHEET_POOL_SIZE_BYTES
+                                          : desc->sprite_sheet_pool_size_bytes;
+
+  const int screen_size = desc->screen_width * desc->screen_height;
+  if (!(iso->screen = calloc(screen_size, sizeof(Pixel)))) {
+    goto cleanup;
+  }
+
+  return iso;
+
+cleanup:
+  isogfx_del(&iso);
+  return 0;
+}
+
+/// Destroy the world, its tile set, and the underlying pools.
+static void destroy_world(IsoGfx* iso) {
+  assert(iso);
+  if (iso->world) {
+    free(iso->world);
+    iso->world = 0;
+  }
+  mempool_del(&iso->tiles);
+  mem_del(&iso->pixels);
+}
+
+/// Destroy all loaded sprites and the underlying pools.
+static void destroy_sprites(IsoGfx* iso) {
+  assert(iso);
+  mempool_del(&iso->sprites);
+  mem_del(&iso->sheets);
+}
+
+void isogfx_del(IsoGfx** pIso) {
+  assert(pIso);
+  IsoGfx* iso = *pIso;
+  if (iso) {
+    destroy_world(iso);
+    destroy_sprites(iso);
+    if (iso->screen) {
+      free(iso->screen);
+      iso->screen = 0;
+    }
+    free(iso);
+    *pIso = 0;
+  }
+}
+
+bool isogfx_make_world(IsoGfx* iso, const WorldDesc* desc) {
+  assert(iso);
+  assert(desc);
+  assert(desc->tile_width > 0);
+  assert(desc->tile_height > 0);
+  // Part of our implementation assumes even widths and heights for greater
+  // precision.
+  assert((desc->tile_width & 1) == 0);
+  assert((desc->tile_height & 1) == 0);
+
+  // Handle recreation by destroying the previous world.
+  destroy_world(iso);
+
+  iso->tile_width   = desc->tile_width;
+  iso->tile_height  = desc->tile_height;
+  iso->world_width  = desc->world_width;
+  iso->world_height = desc->world_height;
+
+  const int world_size      = desc->world_width * desc->world_height;
+  const int tile_size       = desc->tile_width * desc->tile_height;
+  const int tile_size_bytes = tile_size * (int)sizeof(Pixel);
+  const int tile_pool_size =
+      desc->max_num_tiles > 0 ? desc->max_num_tiles : DEFAULT_MAX_NUM_TILES;
+
+  if (!(iso->world = calloc(world_size, sizeof(Tile)))) {
+    goto cleanup;
+  }
+  if (!mempool_make_dyn(&iso->tiles, world_size, sizeof(TileData))) {
+    goto cleanup;
+  }
+  if (!mem_make_dyn(&iso->pixels, tile_pool_size, tile_size_bytes)) {
+    goto cleanup;
+  }
+
+  return true;
+
+cleanup:
+  destroy_world(iso);
+  return false;
+}
+
+bool isogfx_load_world(IsoGfx* iso, const char* filepath) {
+  assert(iso);
+  assert(filepath);
+
+  bool success = false;
+
+  // Handle recreation by destroying the previous world.
+  destroy_world(iso);
+
+  // Load the map.
+  printf("Load tile map: %s\n", filepath);
+  Tm_Map* map = read_file(filepath);
+  if (!map) {
+    goto cleanup;
+  }
+
+  // Allocate memory for the map and tile sets.
+  const int world_size           = map->world_width * map->world_height;
+  const int base_tile_size       = map->base_tile_width * map->base_tile_height;
+  const int base_tile_size_bytes = base_tile_size * (int)sizeof(Pixel);
+  // TODO: Need to get the total number of tiles from the map.
+  const int tile_pool_size = DEFAULT_MAX_NUM_TILES;
+
+  if (!(iso->world = calloc(world_size, sizeof(Tile)))) {
+    goto cleanup;
+  }
+  if (!mempool_make_dyn(&iso->tiles, tile_pool_size, sizeof(TileData))) {
+    goto cleanup;
+  }
+  if (!mem_make_dyn(&iso->pixels, tile_pool_size, base_tile_size_bytes)) {
+    goto cleanup;
+  }
+
+  // Load the tile sets.
+  const Tm_Layer* layer = &map->layers[0];
+  // TODO: Handle num_layers layers.
+  for (int i = 0; i < 1; ++i) {
+    const char* ts_path = layer->tileset_path;
+
+    // Tile set path is relative to the tile map file. Make it relative to the
+    // current working directory before loading.
+    char ts_path_cwd[PATH_MAX] = {0};
+    if (!path_make_relative(filepath, ts_path, ts_path_cwd, PATH_MAX)) {
+      goto cleanup;
+    }
+
+    Ts_TileSet* tileset = read_file(ts_path_cwd);
+    if (!tileset) {
+      goto cleanup;
+    };
+
+    // Load tile data.
+    const Ts_Tile* tile = &tileset->tiles[0];
+    for (uint16_t j = 0; j < tileset->num_tiles; ++j) {
+      // Tile dimensions should be a multiple of the base tile size.
+      assert((tile->width % map->base_tile_width) == 0);
+      assert((tile->height % map->base_tile_height) == 0);
+
+      // Allocate N base tile size blocks for the tile.
+      const uint16_t tile_size  = tile->width * tile->height;
+      const int      num_blocks = tile_size / base_tile_size;
+      Pixel*         pixels     = mem_alloc(&iso->pixels, num_blocks);
+      assert(pixels);
+      memcpy(pixels, tile->pixels, tile_size * sizeof(Pixel));
+
+      // Allocate the tile data.
+      TileData* tile_data = mempool_alloc(&iso->tiles);
+      assert(tile_data);
+      tile_data->width  = tile->width;
+      tile_data->height = tile->height;
+      tile_data->pixels_handle =
+          (uint16_t)mem_get_chunk_handle(&iso->pixels, pixels);
+
+      tile = ts_tileset_get_next_tile(tileset, tile);
+    }
+
+    printf("Loaded tile set (%u tiles): %s\n", tileset->num_tiles, ts_path_cwd);
+
+    free(tileset);
+    layer = tm_map_get_next_layer(map, layer);
+  }
+
+  // Load the map into the world.
+  layer = &map->layers[0];
+  // TODO: Handle num_layers layers.
+  for (int i = 0; i < 1; ++i) {
+    memcpy(iso->world, layer->tiles, world_size * sizeof(Tile));
+
+    // TODO: We need to handle 'firsgid' in TMX files.
+    for (int j = 0; j < world_size; ++j) {
+      iso->world[j] -= 1;
+    }
+
+    layer = tm_map_get_next_layer(map, layer);
+  }
+
+  iso->world_width  = map->world_width;
+  iso->world_height = map->world_height;
+  iso->tile_width   = map->base_tile_width;
+  iso->tile_height  = map->base_tile_height;
+
+  success = true;
+
+cleanup:
+  if (map) {
+    free(map);
+  }
+  if (!success) {
+    destroy_world(iso);
+  }
+  return success;
+}
+
+int isogfx_world_width(const IsoGfx* iso) {
+  assert(iso);
+  return iso->world_width;
+}
+
+int isogfx_world_height(const IsoGfx* iso) {
+  assert(iso);
+  return iso->world_height;
+}
+
+/// Create a tile mask procedurally.
+static void make_tile_from_colour(
+    const IsoGfx* iso, Pixel colour, TileData* tile) {
+  assert(iso);
+  assert(tile);
+
+  const int width  = tile->width;
+  const int height = tile->height;
+  const int r      = width / height;
+
+  for (int y = 0; y < height / 2; ++y) {
+    const int mask_start = width / 2 - r * y - 1;
+    const int mask_end   = width / 2 + r * y + 1;
+    for (int x = 0; x < width; ++x) {
+      const bool  mask = (mask_start <= x) && (x <= mask_end);
+      const Pixel val = mask ? colour : (Pixel){.r = 0, .g = 0, .b = 0, .a = 0};
+
+      // Top half.
+      *tile_xy_mut(iso, tile, x, y) = val;
+
+      // Bottom half reflects the top half.
+      const int y_reflected                   = height - y - 1;
+      *tile_xy_mut(iso, tile, x, y_reflected) = val;
+    }
+  }
+}
+
+Tile isogfx_make_tile(IsoGfx* iso, const TileDesc* desc) {
+  assert(iso);
+  assert(desc);
+  // Client must create world before creating tiles.
+  assert(iso->tile_width > 0);
+  assert(iso->tile_height > 0);
+
+  TileData* tile = mempool_alloc(&iso->tiles);
+  assert(tile); // TODO: Make this a hard assert.
+
+  const int num_blocks = calc_num_tile_blocks(
+      iso->tile_width, iso->tile_height, desc->width, desc->height);
+
+  Pixel* pixels = mem_alloc(&iso->pixels, num_blocks);
+  assert(pixels); // TODO: Make this a hard assert.
+
+  tile->width         = desc->width;
+  tile->height        = desc->height;
+  tile->pixels_handle = mem_get_chunk_handle(&iso->pixels, pixels);
+
+  switch (desc->type) {
+  case TileFromColour:
+    make_tile_from_colour(iso, desc->colour, tile);
+    break;
+  case TileFromFile:
+    assert(false); // TODO
+    break;
+  case TileFromMemory:
+    assert(false); // TODO
+    break;
+  }
+
+  return (Tile)mempool_get_block_index(&iso->tiles, tile);
+}
+
+void isogfx_set_tile(IsoGfx* iso, int x, int y, Tile tile) {
+  assert(iso);
+  *world_xy_mut(iso, x, y) = tile;
+}
+
+void isogfx_set_tiles(IsoGfx* iso, int x0, int y0, int x1, int y1, Tile tile) {
+  assert(iso);
+  for (int y = y0; y < y1; ++y) {
+    for (int x = x0; x < x1; ++x) {
+      isogfx_set_tile(iso, x, y, tile);
+    }
+  }
+}
+
+bool isogfx_load_sprite_sheet(
+    IsoGfx* iso, const char* filepath, SpriteSheet* p_sheet) {
+  assert(iso);
+  assert(filepath);
+  assert(p_sheet);
+
+  bool success = false;
+
+  // Lazy initialization of sprite pools.
+  if (mempool_capacity(&iso->sprites) == 0) {
+    if (!mempool_make_dyn(
+            &iso->sprites, iso->max_num_sprites, sizeof(SpriteData))) {
+      return false;
+    }
+  }
+  if (mem_capacity(&iso->sheets) == 0) {
+    // Using a block size of 1 byte for sprite sheet data.
+    if (!mem_make_dyn(&iso->sheets, iso->sprite_sheet_pool_size_bytes, 1)) {
+      return false;
+    }
+  }
+
+  // Load sprite sheet file.
+  printf("Load sprite sheet: %s\n", filepath);
+  FILE* file = fopen(filepath, "rb");
+  if (file == NULL) {
+    goto cleanup;
+  }
+  const size_t     sheet_size = get_file_size(file);
+  SpriteSheetData* ss_sheet   = mem_alloc(&iso->sheets, sheet_size);
+  if (!ss_sheet) {
+    goto cleanup;
+  }
+  if (fread(ss_sheet, sheet_size, 1, file) != 1) {
+    goto cleanup;
+  }
+
+  *p_sheet = mem_get_chunk_handle(&iso->sheets, ss_sheet);
+  success  = true;
+
+cleanup:
+  // Pools remain initialized since client may attempt to load other sprites.
+  if (file != NULL) {
+    fclose(file);
+  }
+  if (!success) {
+    if (ss_sheet) {
+      mem_free(&iso->sheets, &ss_sheet);
+    }
+  }
+  return success;
+}
+
+Sprite isogfx_make_sprite(IsoGfx* iso, SpriteSheet sheet) {
+  assert(iso);
+
+  SpriteData* sprite = mempool_alloc(&iso->sprites);
+  assert(sprite);
+
+  sprite->sheet = sheet;
+
+  return mempool_get_block_index(&iso->sprites, sprite);
+}
+
+#define with_sprite(SPRITE, BODY)                                \
+  {                                                              \
+    SpriteData* data = mempool_get_block(&iso->sprites, sprite); \
+    assert(data);                                                \
+    BODY;                                                        \
+  }
+
+void isogfx_set_sprite_position(IsoGfx* iso, Sprite sprite, int x, int y) {
+  assert(iso);
+  with_sprite(sprite, {
+    data->position.x = x;
+    data->position.y = y;
+  });
+}
+
+void isogfx_set_sprite_animation(IsoGfx* iso, Sprite sprite, int animation) {
+  assert(iso);
+  with_sprite(sprite, { data->animation = animation; });
+}
+
+void isogfx_update(IsoGfx* iso, double t) {
+  assert(iso);
+
+  // If this is the first time update() is called after initialization, just
+  // record the starting animation time.
+  if (iso->last_animation_time == 0.0) {
+    iso->last_animation_time = t;
+    return;
+  }
+
+  if ((t - iso->last_animation_time) >= ANIMATION_UPDATE_DELTA) {
+    // TODO: Consider linking animated sprites in a list so that we only walk
+    // over those here and not also the static sprites.
+    mempool_foreach(&iso->sprites, sprite, {
+      const SpriteSheetData* sheet = mem_get_chunk(&iso->sheets, sprite->sheet);
+      assert(sheet); // TODO: Make this a hard assert inside the mem/pool.
+      const SpriteSheetRow* row =
+          get_sprite_sheet_row(sheet, sprite->animation);
+      sprite->frame = (sprite->frame + 1) % row->num_cols;
+    });
+
+    iso->last_animation_time = t;
+  }
+}
+
+// -----------------------------------------------------------------------------
+// Rendering and picking.
+// -----------------------------------------------------------------------------
+
+typedef struct CoordSystem {
+  ivec2 o; /// Origin.
+  ivec2 x;
+  ivec2 y;
+} CoordSystem;
+
+/// Create the basis for the isometric coordinate system with origin and vectors
+/// expressed in the Cartesian system.
+static CoordSystem make_iso_coord_system(const IsoGfx* iso) {
+  assert(iso);
+  const ivec2 o = {iso->screen_width / 2, 0};
+  const ivec2 x = {.x = iso->tile_width / 2, .y = iso->tile_height / 2};
+  const ivec2 y = {.x = -iso->tile_width / 2, .y = iso->tile_height / 2};
+  return (CoordSystem){o, x, y};
+}
+
+/// Get the screen position of the top diamond-corner of the tile at world
+/// (x,y).
+static ivec2 GetTileScreenOrigin(
+    const CoordSystem iso_space, int world_x, int world_y) {
+  const ivec2 vx_offset = ivec2_scale(iso_space.x, world_x);
+  const ivec2 vy_offset = ivec2_scale(iso_space.y, world_y);
+  const ivec2 screen_origin =
+      ivec2_add(iso_space.o, ivec2_add(vx_offset, vy_offset));
+
+  return screen_origin;
+}
+
+static Pixel alpha_blend(Pixel src, Pixel dst) {
+  if ((src.a == 255) || (dst.a == 0)) {
+    return src;
+  }
+  const uint16_t one_minus_alpha = 255 - src.a;
+#define blend(s, d)                             \
+  (Channel)(                                    \
+      (double)((uint16_t)s * (uint16_t)src.a +  \
+               (uint16_t)d * one_minus_alpha) / \
+      255.0)
+  return (Pixel){
+      .r = blend(src.r, dst.r),
+      .g = blend(src.g, dst.g),
+      .b = blend(src.b, dst.b),
+      .a = src.a};
+}
+
+/// Draw a rectangle (tile or sprite).
+///
+/// The rectangle's top-left corner is mapped to the screen space position given
+/// by 'top_left'.
+///
+/// The rectangle's pixels are assumed to be arranged in a linear, row-major
+/// fashion.
+///
+/// If indices are given, then the image is assumed to be colour-paletted, where
+/// 'pixels' is the palette and 'indices' the pixel indices. Otherwise, the
+/// image is assumed to be in plain RGBA format.
+static void draw_rect(
+    IsoGfx* iso, ivec2 top_left, int rect_width, int rect_height,
+    const Pixel* pixels, const uint8_t* indices) {
+  assert(iso);
+
+#define rect_pixel(X, Y) \
+  (indices ? pixels[indices[Y * rect_width + X]] : pixels[Y * rect_width + X])
+
+  // Rect origin can be outside screen bounds, so we must offset accordingly to
+  // draw only the visible portion.
+#define max(a, b) (a > b ? a : b)
+  const int px_offset = max(0, -top_left.x);
+  const int py_offset = max(0, -top_left.y);
+
+  // Rect can exceed screen bounds, so clip along Y and X as we draw.
+  for (int py = py_offset;
+       (py < rect_height) && (top_left.y + py < iso->screen_height); ++py) {
+    const int sy = top_left.y + py;
+    for (int px = px_offset;
+         (px < rect_width) && (top_left.x + px < iso->screen_width); ++px) {
+      const Pixel colour = rect_pixel(px, py);
+      if (colour.a > 0) {
+        const int   sx              = top_left.x + px;
+        const Pixel dst             = screen_xy(iso, sx, sy);
+        const Pixel final           = alpha_blend(colour, dst);
+        *screen_xy_mut(iso, sx, sy) = final;
+      }
+    }
+  }
+}
+
+/// Draw a tile.
+///
+/// 'screen_origin' is the screen coordinates of the top diamond-corner of the
+/// tile (the base tile for super tiles).
+///     World (0, 0) -> (screen_width / 2, 0).
+static void draw_tile(IsoGfx* iso, ivec2 screen_origin, Tile tile) {
+  assert(iso);
+
+  const TileData* tile_data = mempool_get_block(&iso->tiles, tile);
+  assert(tile_data);
+  const Pixel* pixels = tile_xy_const_ref(iso, tile_data, 0, 0);
+
+  // Move from the top diamond-corner to the top-left corner of the tile image.
+  // For regular tiles, tile height == base tile height, so the y offset is 0.
+  // For super tiles, move as high up as the height of the tile.
+  const ivec2 offset = {
+      -(iso->tile_width / 2), tile_data->height - iso->tile_height};
+  const ivec2 top_left = ivec2_add(screen_origin, offset);
+
+  draw_rect(iso, top_left, tile_data->width, tile_data->height, pixels, 0);
+}
+
+static void draw_world(IsoGfx* iso) {
+  assert(iso);
+
+  const int W = iso->screen_width;
+  const int H = iso->screen_height;
+
+  memset(iso->screen, 0, W * H * sizeof(Pixel));
+
+  const CoordSystem iso_space = make_iso_coord_system(iso);
+
+  // TODO: Culling.
+  // Ex: map the screen corners to tile space to cull.
+  // Ex: walk in screen space and fetch the tile.
+  // The tile-centric approach might be more cache-friendly since the
+  // screen-centric approach would juggle multiple tiles throughout the scan.
+  for (int wy = 0; wy < iso->world_height; ++wy) {
+    for (int wx = 0; wx < iso->world_width; ++wx) {
+      const Tile  tile          = world_xy(iso, wx, wy);
+      const ivec2 screen_origin = GetTileScreenOrigin(iso_space, wx, wy);
+      draw_tile(iso, screen_origin, tile);
+    }
+  }
+}
+
+static void draw_sprite(
+    IsoGfx* iso, ivec2 origin, const SpriteData* sprite,
+    const SpriteSheetData* sheet) {
+  assert(iso);
+  assert(sprite);
+  assert(sheet);
+  assert(sprite->animation >= 0);
+  assert(sprite->animation < sheet->num_rows);
+  assert(sprite->frame >= 0);
+
+  const SpriteSheetRow* row = get_sprite_sheet_row(sheet, sprite->animation);
+  const uint8_t* frame = get_sprite_sheet_sprite(sheet, row, sprite->frame);
+  draw_rect(
+      iso, origin, sheet->sprite_width, sheet->sprite_height,
+      sheet->palette.colours, frame);
+}
+
+static void draw_sprites(IsoGfx* iso) {
+  assert(iso);
+
+  const CoordSystem iso_space = make_iso_coord_system(iso);
+
+  mempool_foreach(&iso->sprites, sprite, {
+    const SpriteSheetData* sheet = mem_get_chunk(&iso->sheets, sprite->sheet);
+    assert(sheet);
+
+    const ivec2 screen_origin =
+        GetTileScreenOrigin(iso_space, sprite->position.x, sprite->position.y);
+    draw_sprite(iso, screen_origin, sprite, sheet);
+  });
+}
+
+void isogfx_render(IsoGfx* iso) {
+  assert(iso);
+  draw_world(iso);
+  draw_sprites(iso);
+}
+
+void isogfx_draw_tile(IsoGfx* iso, int x, int y, Tile tile) {
+  assert(iso);
+  assert(x >= 0);
+  assert(y >= 0);
+  assert(x < iso->world_width);
+  assert(y < iso->world_height);
+
+  const CoordSystem iso_space     = make_iso_coord_system(iso);
+  const ivec2       screen_origin = GetTileScreenOrigin(iso_space, x, y);
+  draw_tile(iso, screen_origin, tile);
+}
+
+bool isogfx_resize(IsoGfx* iso, int screen_width, int screen_height) {
+  assert(iso);
+  assert(iso->screen);
+
+  const int current_size = iso->screen_width * iso->screen_height;
+  const int new_size     = screen_width * screen_height;
+
+  if (new_size > current_size) {
+    Pixel* new_screen = calloc(new_size, sizeof(Pixel));
+    if (new_screen) {
+      free(iso->screen);
+      iso->screen = new_screen;
+    } else {
+      return false;
+    }
+  }
+  iso->screen_width  = screen_width;
+  iso->screen_height = screen_height;
+  return true;
+}
+
+void isogfx_get_screen_size(const IsoGfx* iso, int* width, int* height) {
+  assert(iso);
+  assert(width);
+  assert(height);
+  *width  = iso->screen_width;
+  *height = iso->screen_height;
+}
+
+const Pixel* isogfx_get_screen_buffer(const IsoGfx* iso) {
+  assert(iso);
+  return iso->screen;
+}
+
+void isogfx_pick_tile(
+    const IsoGfx* iso, double xcart, double ycart, int* xiso, int* yiso) {
+  assert(iso);
+  assert(xiso);
+  assert(yiso);
+
+  const vec2 xy_iso = cart2iso(
+      (vec2){.x = xcart, .y = ycart}, iso->tile_width, iso->tile_height,
+      iso->screen_width);
+
+  if ((0 <= xy_iso.x) && (xy_iso.x < iso->world_width) && (0 <= xy_iso.y) &&
+      (xy_iso.y < iso->world_height)) {
+    *xiso = (int)xy_iso.x;
+    *yiso = (int)xy_iso.y;
+  } else {
+    *xiso = -1;
+    *yiso = -1;
+  }
+}
diff --git a/tools/mkasset.py b/tools/mkasset.py
new file mode 100644
index 0000000..3ca8a1d
--- /dev/null
+++ b/tools/mkasset.py
@@ -0,0 +1,324 @@
+# Converts assets to binary formats (.ts, .tm, .ss) for the engine.
+#
+# Input file formats:
+#  - Tiled tile set (.tsx)
+#  - Tiled tile map (.tmx)
+#  - Sprite sheets (.jpg, .png, etc), 1 row per animation.
+#
+# Output file formats:
+#  - Binary tile set file (.ts)
+#  - Binary tile map file (.tm)
+#  - Binary sprite sheet file (.ss)
+#
+import argparse
+import ctypes
+import os
+from PIL import Image
+import sys
+from xml.etree import ElementTree
+
+# Maximum length of path strings in .TS and .TM files.
+# Must match the engine's value.
+MAX_PATH_LENGTH = 128
+
+
+def drop_extension(filepath):
+    return filepath[:filepath.rfind('.')]
+
+
+def to_char_array(string, length):
+    """Convert a string to a fixed-length ASCII char array.
+
+    The length of str must be at most length-1 so that the resulting string can
+    be null-terminated.
+    """
+    assert (len(string) < length)
+    chars = string.encode("ascii")
+    nulls = ("\0" * (length - len(string))).encode("ascii")
+    return chars + nulls
+
+
+def convert_tsx(input_filepath, output_filepath):
+    """Converts a Tiled .tsx tileset file to a .TS tile set file."""
+    xml = ElementTree.parse(input_filepath)
+    root = xml.getroot()
+
+    tile_count = int(root.attrib["tilecount"])
+    max_tile_width = int(root.attrib["tilewidth"])
+    max_tile_height = int(root.attrib["tileheight"])
+
+    print(f"Tile count: {tile_count}")
+    print(f"Max width:  {max_tile_width}")
+    print(f"Max height: {max_tile_height}")
+
+    with open(output_filepath, 'bw') as output:
+        output.write(ctypes.c_uint16(tile_count))
+        output.write(ctypes.c_uint16(max_tile_width))
+        output.write(ctypes.c_uint16(max_tile_height))
+
+        num_tile = 0
+        for tile in root:
+            # Skip the "grid" and other non-tile elements.
+            if not tile.tag == "tile":
+                continue
+
+            # Assuming tiles are numbered 0..N.
+            tile_id = int(tile.attrib["id"])
+            assert (tile_id == num_tile)
+            num_tile += 1
+
+            image = tile[0]
+            tile_width = int(image.attrib["width"])
+            tile_height = int(image.attrib["height"])
+            tile_path = image.attrib["source"]
+
+            output.write(ctypes.c_uint16(tile_width))
+            output.write(ctypes.c_uint16(tile_height))
+
+            with Image.open(tile_path) as im:
+                bytes = im.convert('RGBA').tobytes()
+                output.write(bytes)
+
+
+def convert_tmx(input_filepath, output_filepath):
+    """Converts a Tiled .tmx file to a .TM tile map file."""
+    xml = ElementTree.parse(input_filepath)
+    root = xml.getroot()
+
+    map_width = int(root.attrib["width"])
+    map_height = int(root.attrib["height"])
+    base_tile_width = int(root.attrib["tilewidth"])
+    base_tile_height = int(root.attrib["tileheight"])
+    num_layers = 1
+
+    print(f"Map width:   {map_width}")
+    print(f"Map height:  {map_height}")
+    print(f"Tile width:  {base_tile_width}")
+    print(f"Tile height: {base_tile_height}")
+
+    with open(output_filepath, 'bw') as output:
+        output.write(ctypes.c_uint16(map_width))
+        output.write(ctypes.c_uint16(map_height))
+        output.write(ctypes.c_uint16(base_tile_width))
+        output.write(ctypes.c_uint16(base_tile_height))
+        output.write(ctypes.c_uint16(num_layers))
+
+        tileset_path = None
+
+        for child in root:
+            if child.tag == "tileset":
+                tileset = child
+                tileset_path = tileset.attrib["source"]
+
+                print(f"Tile set: {tileset_path}")
+
+                tileset_path = tileset_path.replace("tsx", "ts")
+            elif child.tag == "layer":
+                layer = child
+                layer_id = int(layer.attrib["id"])
+                layer_width = int(layer.attrib["width"])
+                layer_height = int(layer.attrib["height"])
+
+                print(f"Layer:  {layer_id}")
+                print(f"Width:  {layer_width}")
+                print(f"Height: {layer_height}")
+
+                assert (tileset_path)
+                output.write(to_char_array(tileset_path, MAX_PATH_LENGTH))
+
+                # Assume the layer's dimensions matches the map's.
+                assert (layer_width == map_width)
+                assert (layer_height == map_height)
+
+                data = layer[0]
+                # Handle other encodings later.
+                assert (data.attrib["encoding"] == "csv")
+
+                csv = data.text.strip()
+                rows = csv.split('\n')
+                for row in rows:
+                    tile_ids = [x.strip() for x in row.split(',') if x]
+                    for tile_id in tile_ids:
+                        output.write(ctypes.c_uint16(int(tile_id)))
+
+
+def get_num_cols(image, sprite_width):
+    """Return the number of non-empty columns in the image.
+
+    Assumes no gaps in the columns.
+    """
+    assert (image.width % sprite_width == 0)
+    num_cols = image.width // sprite_width
+
+    # Start the search from right to left.
+    for col in reversed(range(1, num_cols)):
+        left = (col - 1) * sprite_width
+        right = col * sprite_width
+        rect = image.crop((left, 0, right, image.height))
+        min_max = rect.getextrema()
+        for (channel_min, channel_max) in min_max:
+            if channel_min != 0 or channel_max != 0:
+                # 'col' is the rightmost non-empty column.
+                # Assuming no gaps, col+1 is the number of non-empty columns.
+                return col + 1
+
+    return 0
+
+
+def get_sprite_sheet_rows(im, sprite_width, sprite_height):
+    """Gets the individual rows of a sprite sheet.
+
+    The input sprite sheet can have any number of rows.
+
+    Returns a list of lists [[sprite]], one inner list for the columns in each
+    row.
+    """
+    # Sprite sheet's width and height must be integer multiples of the
+    # sprite's width and height.
+    assert (im.width % sprite_width == 0)
+    assert (im.height % sprite_height == 0)
+
+    num_rows = im.height // sprite_height
+
+    rows = []
+    for row in range(num_rows):
+        # Get the number of columns.
+        upper = row * sprite_height
+        lower = (row + 1) * sprite_height
+        whole_row = im.crop((0, upper, im.width, lower))
+        num_cols = get_num_cols(whole_row, sprite_width)
+        assert (num_cols > 0)
+
+        # Crop the row into N columns.
+        cols = []
+        for i in range(num_cols):
+            left = i * sprite_width
+            right = (i + 1) * sprite_width
+            sprite = im.crop((left, upper, right, lower))
+            cols.append(sprite)
+
+        assert (len(cols) == num_cols)
+        rows.append(cols)
+
+    return rows
+
+
+def make_image_from_rows(rows, sprite_width, sprite_height):
+    """Concatenate the rows into a single RGBA image."""
+    im_width = sprite_width * max(len(row) for row in rows)
+    im_height = len(rows) * sprite_height
+    im = Image.new('RGBA', (im_width, im_height))
+    y = 0
+    for row in rows:
+        x = 0
+        for sprite in row:
+            im.paste(sprite.convert('RGBA'), (x, y))
+            x += sprite_width
+        y += sprite_height
+    return im
+
+
+def convert_sprite_sheet(input_file_paths, sprite_width, sprite_height,
+                         output_filepath):
+    """Converts a set of sprite sheet images into a binary sprite sheet file
+    (.ss).
+
+    The input sprite sheets can have any number of rows, one row per animation.
+    All rows from all sprite sheets are concatenated in the output file.
+
+    The sprite's width and height is assumed constant throughout the input
+    sprite sheets.
+    """
+    rows = []
+    for input_filepath in input_file_paths:
+        with Image.open(input_filepath) as sprite_sheet:
+            rows.extend(
+                get_sprite_sheet_rows(sprite_sheet, sprite_width,
+                                      sprite_height))
+
+    im = make_image_from_rows(rows, sprite_width, sprite_height)
+    im = im.convert(mode="P", palette=Image.ADAPTIVE, colors=256)
+
+    # The sprite data in 'rows' is no longer needed.
+    # Keep just the number of columns per row.
+    rows = [len(row) for row in rows]
+
+    with open(output_filepath, 'bw') as output:
+        output.write(ctypes.c_uint16(sprite_width))
+        output.write(ctypes.c_uint16(sprite_height))
+        output.write(ctypes.c_uint16(len(rows)))
+
+        # Write palette.
+        # getpalette() returns 256 colors, but the palette might use less than
+        # that. getcolors() returns the number of unique colors.
+        # getpalette() also returns a flattened list, which is why we must *4.
+        num_colours = len(im.getcolors())
+        colours = im.getpalette(rawmode="RGBA")[:4 * num_colours]
+        palette = []
+        for i in range(0, 4 * num_colours, 4):
+            palette.append((colours[i], colours[i + 1], colours[i + 2],
+                            colours[i + 3]))
+
+        output.write(ctypes.c_uint16(len(palette)))
+        output.write(bytearray(colours))
+
+        print(f"Sprite width:  {sprite_width}")
+        print(f"Sprite height: {sprite_height}")
+        print(f"Rows:          {len(rows)}")
+        print(f"Colours:       {len(palette)}")
+
+        # print("Palette")
+        # for i, colour in enumerate(palette):
+        #     print(f"{i}: {colour}")
+
+        for row, num_columns in enumerate(rows):
+            output.write(ctypes.c_uint16(num_columns))
+            upper = row * sprite_height
+            lower = (row + 1) * sprite_height
+            for col in range(num_columns):
+                left = col * sprite_width
+                right = (col + 1) * sprite_width
+                sprite = im.crop((left, upper, right, lower))
+                sprite_bytes = sprite.tobytes()
+
+                assert (len(sprite_bytes) == sprite_width * sprite_height)
+                output.write(sprite_bytes)
+
+                # if (row == 0) and (col == 0):
+                #     print(f"Sprite: ({len(sprite_bytes)})")
+                #     print(list(sprite_bytes))
+                #     sprite.save("out.png")
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("input",
+                        nargs="+",
+                        help="Input file (.tsx, .tmx) or path regex (sprite sheets)")
+    parser.add_argument("--width", type=int, help="Sprite width in pixels")
+    parser.add_argument("--height", type=int, help="Sprite height in pixels")
+    parser.add_argument("--out", help="Output file (sprite sheets)")
+    args = parser.parse_args()
+
+    if ".tsx" in args.input:
+        output_filepath_no_ext = drop_extension(args.input)
+        output_filepath = output_filepath_no_ext + ".ts"
+        convert_tsx(args.input, output_filepath)
+    elif ".tmx" in args.input:
+        output_filepath_no_ext = drop_extension(args.input)
+        output_filepath = output_filepath_no_ext + ".tm"
+        convert_tmx(args.input, output_filepath)
+    else:
+        # Sprite sheets.
+        if not args.width or not args.height:
+            print("Sprite width and height must be given")
+            return 1
+        output_filepath = args.out if args.out else "out.ss"
+        convert_sprite_sheet(args.input, args.width, args.height,
+                             output_filepath)
+
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())