Fix T64625: Eevee image textures with alpha have dark edges

Now texture storage of images is defined by the alpha mode of the image. The
downside of this is that there can be artifacts near alpha edges where pixels
with zero alpha bleed in. It also adds more code complexity since image textures
are no longer all stored the same way.

This changes allows us to keep using sRGB texture formats, which have edge
darkening when stored with premultiplied alpha. Game engines seems to generally
do the same thing, and we want to be compatible with them.

1 files changed, 5 insertions, 2 deletions

diff --git a/source/blender/draw/modes/object_mode.c b/source/blender/draw/modes/object_mode.c
index 8dae160682a..bbf364960c9 100644
--- a/source/blender/draw/modes/object_mode.c
+++ b/source/blender/draw/modes/object_mode.c
@@ -974,9 +974,10 @@ static void DRW_shgroup_empty_image(OBJECT_Shaders *sh_data,
 
   const bool use_alpha_blend = (ob->empty_image_flag & OB_EMPTY_IMAGE_USE_ALPHA_BLEND) != 0;
   GPUTexture *tex = NULL;
+  Image *ima = ob->data;
 
-  if (ob->data != NULL) {
-    tex = GPU_texture_from_blender(ob->data, ob->iuser, GL_TEXTURE_2D);
+  if (ima != NULL) {
+    tex = GPU_texture_from_blender(ima, ob->iuser, GL_TEXTURE_2D);
     if (tex) {
       size[0] = GPU_texture_width(tex);
       size[1] = GPU_texture_height(tex);
@@ -1023,6 +1024,8 @@ static void DRW_shgroup_empty_image(OBJECT_Shaders *sh_data,
     DRW_shgroup_uniform_float(grp, "size", &ob->empty_drawsize, 1);
     DRW_shgroup_uniform_vec2(grp, "offset", ob->ima_ofs, 1);
     DRW_shgroup_uniform_texture(grp, "image", tex);
+    DRW_shgroup_uniform_bool_copy(
+        grp, "imagePremultiplied", (ima->alpha_mode == IMA_ALPHA_PREMUL));
     DRW_shgroup_uniform_vec4(grp, "objectColor", ob->color, 1);
     DRW_shgroup_uniform_bool_copy(grp, "useAlphaTest", !use_alpha_blend);
     if (sh_cfg == GPU_SHADER_CFG_CLIPPED) {