assume constant dimensions for created textures, shaves a lot of time in uploading

src/rendering/twn_gl_any_rendering.c

@@ -119,11 +119,14 @@ GLuint get_scratch_vertex_array(void) {
 }
 
 
-GPUTexture create_gpu_texture(TextureFilter filter, bool generate_mipmaps) {
+GPUTexture create_gpu_texture(TextureFilter filter, bool generate_mipmaps, int channels, int width, int height) {
     GLuint texture;
     glGenTextures(1, &texture);
     glBindTexture(GL_TEXTURE_2D, texture);
 
+    SDL_assert(width > 0 && height > 0);
+    SDL_assert(channels > 0 && channels <= 4);
+
 #if !defined(EMSCRIPTEN)
     glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, (GLboolean)generate_mipmaps);
 #else
@@ -146,19 +149,6 @@ GPUTexture create_gpu_texture(TextureFilter filter, bool generate_mipmaps) {
     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
 #endif
 
-    glBindTexture(GL_TEXTURE_2D, 0);
-    return texture;
-}
-
-
-void delete_gpu_texture(GPUTexture texture) {
-    glDeleteTextures(1, &texture);
-}
-
-
-void upload_gpu_texture(GPUTexture texture, void *pixels, int channels, int width, int height) {
-    glBindTexture(GL_TEXTURE_2D, texture);
-
     int format_internal, format;
     if (channels == 4) {
         #ifdef EMSCRIPTEN
@@ -179,9 +169,11 @@ void upload_gpu_texture(GPUTexture texture, void *pixels, int channels, int widt
         format = GL_ALPHA;
     } else {
         CRY("upload_gpu_texture", "Unsupported channel count");
-        return;
+        format_internal = GL_ALPHA;
+        format = GL_ALPHA;
     }
 
+    /* preallocate texture storage in advance */
     glTexImage2D(GL_TEXTURE_2D,
                  0,
                  format_internal,
@@ -190,7 +182,46 @@ void upload_gpu_texture(GPUTexture texture, void *pixels, int channels, int widt
                  0,
                  format,
                  GL_UNSIGNED_BYTE,
-                 pixels);
+                 NULL);
+
+    glBindTexture(GL_TEXTURE_2D, 0);
+    return texture;
+}
+
+
+void delete_gpu_texture(GPUTexture texture) {
+    glDeleteTextures(1, &texture);
+}
+
+
+void upload_gpu_texture(GPUTexture texture, void *pixels, int channels, int width, int height) {
+    glBindTexture(GL_TEXTURE_2D, texture);
+
+    int format;
+    if (channels == 4) {
+        format = GL_RGBA;
+    } else if (channels == 3) {
+        format = GL_RGB;
+    } else if (channels == 1) {
+        format = GL_ALPHA;
+    } else {
+        CRY("upload_gpu_texture", "Unsupported channel count");
+        return;
+    }
+
+    profile_start("texture upload");
+
+    glTexSubImage2D(GL_TEXTURE_2D,
+                    0,
+                    0,
+                    0,
+                    width,
+                    height,
+                    format,
+                    GL_UNSIGNED_BYTE,
+                    pixels);
+
+    profile_end("texture upload");
 
     glBindTexture(GL_TEXTURE_2D, 0);
 }

src/rendering/twn_gpu_texture_c.h

@@ -11,7 +11,8 @@ typedef enum TextureFilter {
     TEXTURE_FILTER_LINEAR,
 } TextureFilter;
 
-GPUTexture create_gpu_texture(TextureFilter filter, bool generate_mipmaps);
+/* allocate a texture storage with constant parameters */
+GPUTexture create_gpu_texture(TextureFilter filter, bool generate_mipmaps, int channels, int width, int height);
 
 void delete_gpu_texture(GPUTexture texture);
 

src/rendering/twn_text.c

@@ -150,7 +150,7 @@ static FontData *text_load_font_data(const char *path, int height_px) {
         stbtt_PackEnd(&pctx);
     }
 
-    font_data->texture = create_gpu_texture(ctx.font_filtering, true);
+    font_data->texture = create_gpu_texture(ctx.font_filtering, true, 1, (int)ctx.font_texture_size, (int)ctx.font_texture_size);
     upload_gpu_texture(
         font_data->texture,
         bitmap,

src/twn_textures.c

@@ -193,7 +193,7 @@ static SDL_Surface *create_surface(int width, int height) {
 static void add_new_atlas(TextureCache *cache) {
     SDL_Surface *new_atlas = create_surface((int)ctx.texture_atlas_size, (int)ctx.texture_atlas_size);
     arrput(cache->atlas_surfaces, new_atlas);
-    arrput(cache->atlas_textures, create_gpu_texture(TEXTURE_FILTER_NEAREAST, true));
+    arrput(cache->atlas_textures, create_gpu_texture(TEXTURE_FILTER_NEAREAST, true, 4, (int)ctx.texture_atlas_size, (int)ctx.texture_atlas_size));
 }
 
 
@@ -510,7 +510,7 @@ void textures_update_atlas(TextureCache *cache) {
                 if (!is_power_of_two(response.data->w) || !is_power_of_two(response.data->h))
                     log_warn("Unportable texture dimensions for %s, should be powers of 2", cache->hash[texture_load_queue[i].index].key);
             }
-            response.loner_texture = create_gpu_texture(TEXTURE_FILTER_NEAREAST, true);
+            response.loner_texture = create_gpu_texture(TEXTURE_FILTER_NEAREAST, true, response.data->format->BytesPerPixel, response.data->w, response.data->h);
             upload_texture_from_surface(response.loner_texture, response.data);
             response.srcrect = (Rect) { .w = (float)response.data->w, .h = (float)response.data->h };
 
@@ -642,7 +642,11 @@ void textures_bind_repeating(const TextureCache *cache, TextureKey key) {
 
             const Texture texture = cache->hash[key.id].value;
 
-            const GPUTexture repeating_texture = create_gpu_texture(TEXTURE_FILTER_NEAREAST, false);
+            const GPUTexture repeating_texture = create_gpu_texture(TEXTURE_FILTER_NEAREAST,
+                                                                    false,
+                                                                    texture.data->format->BytesPerPixel,
+                                                                    texture.data->w,
+                                                                    texture.data->h);
 
             SDL_LockSurface(texture.data);