Fix T81026: Image Editor: Alpha (like Bloom) not showing properly

With the new image editor drawing there were was some mutual exclusive
functionality. When rendering the alpha was shown correctly or the pure
emissive colors were shown correctly, but never both. The cause of this
is that the image_gpu did not used the correct alpha mode when generating
gpu textures for non-images (render results, compositors viewer)

The implementation always checked the alpha_mode. Alpha mode is an
attribute for images, but aren't set for non images. This patch adds
a more detailed check to ensure that the gpu texture is premultiplied.

The issue has been tested using several bug report files and production
files.

Reviewed By: Brecht van Lommel

Differential Revision: https://developer.blender.org/D8978

source/blender/blenkernel/BKE_image.h

@@ -382,7 +382,7 @@ struct GPUTexture *BKE_image_get_gpu_tiles(struct Image *image,
 struct GPUTexture *BKE_image_get_gpu_tilemap(struct Image *image,
                                              struct ImageUser *iuser,
                                              struct ImBuf *ibuf);
-
+bool BKE_image_has_gpu_texture_premultiplied_alpha(struct Image *image, struct ImBuf *ibuf);
 void BKE_image_update_gputexture(
     struct Image *ima, struct ImageUser *iuser, int x, int y, int w, int h);
 void BKE_image_paint_set_mipmap(struct Main *bmain, bool mipmap);

source/blender/blenkernel/intern/image_gpu.c

@@ -49,6 +49,21 @@
 static void gpu_free_unused_buffers(void);
 static void image_free_gpu(Image *ima, const bool immediate);
 
+/* Is the alpha of the `GPUTexture` for a given image/ibuf premultiplied. */
+bool BKE_image_has_gpu_texture_premultiplied_alpha(Image *image, ImBuf *ibuf)
+{
+  const bool type_is_premultiplied = (image == NULL) || ELEM(image->type,
+                                                             IMA_TYPE_R_RESULT,
+                                                             IMA_TYPE_COMPOSITE,
+                                                             IMA_TYPE_UV_TEST);
+  const bool store_premultiplied =
+      type_is_premultiplied ||
+      ((ibuf != NULL) &&
+       (ibuf->rect_float ? (image ? (image->alpha_mode != IMA_ALPHA_STRAIGHT) : false) :
+                           (image ? (image->alpha_mode == IMA_ALPHA_PREMUL) : true)));
+  return store_premultiplied;
+}
+
 /* -------------------------------------------------------------------- */
 /** \name UDIM gpu texture
  * \{ */
@@ -198,8 +213,7 @@ static GPUTexture *gpu_texture_create_tile_array(Image *ima, ImBuf *main_ibuf)
     ImBuf *ibuf = BKE_image_acquire_ibuf(ima, &iuser, NULL);
 
     if (ibuf) {
-      const bool store_premultiplied = ibuf->rect_float ? (ima->alpha_mode != IMA_ALPHA_STRAIGHT) :
-                                                          (ima->alpha_mode == IMA_ALPHA_PREMUL);
+      const bool store_premultiplied = BKE_image_has_gpu_texture_premultiplied_alpha(ima, ibuf);
       IMB_update_gpu_texture_sub(tex,
                                  ibuf,
                                  UNPACK2(tileoffset),
@@ -330,9 +344,8 @@ static GPUTexture *image_get_gpu_texture(Image *ima,
   }
   else {
     const bool use_high_bitdepth = (ima->flag & IMA_HIGH_BITDEPTH);
-    const bool store_premultiplied = ibuf_intern->rect_float ?
-                                         (ima ? (ima->alpha_mode != IMA_ALPHA_STRAIGHT) : false) :
-                                         (ima ? (ima->alpha_mode == IMA_ALPHA_PREMUL) : true);
+    const bool store_premultiplied = BKE_image_has_gpu_texture_premultiplied_alpha(ima,
+                                                                                   ibuf_intern);
 
     *tex = IMB_create_gpu_texture(
         ima->id.name + 2, ibuf_intern, use_high_bitdepth, store_premultiplied);
@@ -642,6 +655,7 @@ static void gpu_texture_update_from_ibuf(
   int tex_stride = ibuf->x;
   int tex_offset = ibuf->channels * (y * ibuf->x + x);
 
+  const bool store_premultiplied = BKE_image_has_gpu_texture_premultiplied_alpha(ima, ibuf);
   if (rect_float == NULL) {
     /* Byte pixels. */
     if (!IMB_colormanagement_space_is_data(ibuf->rect_colorspace)) {
@@ -658,15 +672,12 @@ static void gpu_texture_update_from_ibuf(
 
       /* Convert to scene linear with sRGB compression, and premultiplied for
        * correct texture interpolation. */
-      const bool store_premultiplied = (ima->alpha_mode == IMA_ALPHA_PREMUL);
       IMB_colormanagement_imbuf_to_byte_texture(
           rect, x, y, w, h, ibuf, compress_as_srgb, store_premultiplied);
     }
   }
   else {
     /* Float pixels. */
-    const bool store_premultiplied = (ima->alpha_mode != IMA_ALPHA_STRAIGHT);
-
     if (ibuf->channels != 4 || scaled || !store_premultiplied) {
       rect_float = (float *)MEM_mallocN(sizeof(float[4]) * w * h, __func__);
       if (rect_float == NULL) {

source/blender/draw/engines/image/image_engine.c

@@ -138,7 +138,7 @@ static void image_cache_image(IMAGE_Data *vedata, Image *image, ImageUser *iuser
       far_near[0] = ((Camera *)scene->camera->data)->clip_end;
     }
 
-    const bool use_premul_alpha = image->alpha_mode == IMA_ALPHA_PREMUL;
+    const bool use_premul_alpha = BKE_image_has_gpu_texture_premultiplied_alpha(image, ibuf);
     const bool is_tiled_texture = tex_tile_data != NULL;
     const bool do_repeat = (!is_tiled_texture) && ((sima->flag & SI_DRAW_TILE) != 0);