tileset: initial GPU texture atlas w/ procedural sprite painting

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I7b6991f7342362033ad72ab4700fdb9f6a6a6964

libs/tileset/tileset.c

@@ -0,0 +1,118 @@
+#include "tileset.h"
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+int tileset_init(Tileset *ts, int tile_w, int tile_h) {
+  if (ts == NULL)
+    return 0;
+  if (tile_w <= 0 || tile_h <= 0)
+    return 0;
+
+  memset(ts, 0, sizeof(Tileset));
+
+  ts->tile_w = tile_w;
+  ts->tile_h = tile_h;
+
+  // Compute grid dimensions to fit MAX_TILE_ID tiles
+  ts->atlas_cols = 4;                                                    // 4 columns
+  ts->atlas_rows = (MAX_TILE_ID + ts->atlas_cols - 1) / ts->atlas_cols;  // round up
+
+  int atlas_w = ts->atlas_cols * tile_w;
+  int atlas_h = ts->atlas_rows * tile_h;
+
+  // Validate atlas dimensions are reasonable
+  if (atlas_w <= 0 || atlas_h <= 0 || atlas_w > 4096 || atlas_h > 4096)
+    return 0;
+
+  ts->render_target = LoadRenderTexture(atlas_w, atlas_h);
+  if (!IsRenderTextureValid(ts->render_target))
+    return 0;
+
+  // Clear to transparent so unpainted regions don't show artifacts
+  BeginTextureMode(ts->render_target);
+  ClearBackground(BLANK);
+  EndTextureMode();
+
+  ts->finalized = 0;
+  ts->tile_count = 0;
+  return 1;
+}
+
+int tileset_register(Tileset *ts, int id) {
+  if (ts == NULL)
+    return 0;
+  if (id < 0 || id >= MAX_TILE_ID)
+    return 0;
+  if (ts->render_target.id == 0)
+    return 0;
+  if (ts->finalized)
+    return 0;
+  if (ts->regions[id].width != 0)
+    return 0;  // already registered
+
+  int col = id % ts->atlas_cols;
+  int row = id / ts->atlas_cols;
+
+  ts->regions[id] =
+      (Rectangle){(float)(col * ts->tile_w), (float)(row * ts->tile_h), (float)ts->tile_w, (float)ts->tile_h};
+  ts->tile_count++;
+  return 1;
+}
+
+int tileset_finalize(Tileset *ts) {
+  if (ts == NULL)
+    return 0;
+  if (ts->render_target.id == 0)
+    return 0;
+  if (ts->finalized)
+    return 1;  // already finalized
+
+  // Convert RenderTexture to regular Texture2D
+  // RenderTexture textures are flipped vertically in raylib, so we need to handle that
+  Texture2D old_texture = ts->render_target.texture;
+
+  // Create a new texture from the render texture data
+  Image img = LoadImageFromTexture(old_texture);
+  if (img.data == NULL) {
+    return 0;
+  }
+
+  // Flip image vertically because RenderTexture is upside-down
+  ImageFlipVertical(&img);
+
+  Texture2D new_tex = LoadTextureFromImage(img);
+  UnloadImage(img);
+
+  if (new_tex.id == 0) {
+    return 0;
+  }
+
+  // Unload the old render texture and replace with the new regular texture
+  UnloadRenderTexture(ts->render_target);
+  ts->render_target.id = 0;
+  ts->atlas = new_tex;
+  ts->finalized = 1;
+  return 1;
+}
+
+Rectangle tileset_get_region(const Tileset *ts, int id) {
+  if (ts == NULL || id < 0 || id >= MAX_TILE_ID)
+    return (Rectangle){0, 0, 0, 0};
+  if (!ts->finalized)
+    return (Rectangle){0, 0, 0, 0};
+  return ts->regions[id];
+}
+
+void tileset_destroy(Tileset *ts) {
+  if (ts == NULL)
+    return;
+  if (ts->finalized) {
+    if (ts->atlas.id != 0)
+      UnloadTexture(ts->atlas);
+  } else {
+    if (ts->render_target.id != 0)
+      UnloadRenderTexture(ts->render_target);
+  }
+  memset(ts, 0, sizeof(Tileset));
+}