Fix T66100: WorkBench Banding Issues

Color banding issues can appear, as result of the 8 bitdepth RGBA that
is used in the viewport.

This change will use `GPU_RGBA16F` for final renderings and for drawing textures. This
allows displaying HDRI textures. Vertex Colors uses `GPU_RGBA16` to resolve
color banding issues. All other modes use `GPU_RGBA8` to reduce
bandwidth and gpu memory.

Reviewed By: fclem, brecht

Differential Revision: https://developer.blender.org/D5179

4 files changed, 28 insertions, 3 deletions

diff --git a/source/blender/draw/engines/workbench/workbench_deferred.c b/source/blender/draw/engines/workbench/workbench_deferred.c
index 735a0dcf7a0..add49462de1 100644
--- a/source/blender/draw/engines/workbench/workbench_deferred.c
+++ b/source/blender/draw/engines/workbench/workbench_deferred.c
@@ -475,7 +475,7 @@ void workbench_deferred_engine_init(WORKBENCH_Data *vedata)
     const eGPUTextureFormat nor_tex_format = NORMAL_ENCODING_ENABLED() ? GPU_RG16 : GPU_RGBA32F;
     const eGPUTextureFormat comp_tex_format = DRW_state_is_image_render() ? GPU_RGBA16F :
                                                                             GPU_R11F_G11F_B10F;
-    const eGPUTextureFormat col_tex_format = DRW_state_is_image_render() ? GPU_RGBA16F : GPU_RGBA8;
+    const eGPUTextureFormat col_tex_format = workbench_color_texture_format(wpd);
     const eGPUTextureFormat id_tex_format = OBJECT_ID_PASS_ENABLED(wpd) ? GPU_R32UI : GPU_R8;
 
     e_data.object_id_tx = NULL;
diff --git a/source/blender/draw/engines/workbench/workbench_effect_taa.c b/source/blender/draw/engines/workbench/workbench_effect_taa.c
index 88f1f30941a..06442060623 100644
--- a/source/blender/draw/engines/workbench/workbench_effect_taa.c
+++ b/source/blender/draw/engines/workbench/workbench_effect_taa.c
@@ -170,10 +170,10 @@ DRWPass *workbench_taa_create_pass(WORKBENCH_Data *vedata, GPUTexture **color_bu
   WORKBENCH_TextureList *txl = vedata->txl;
   WORKBENCH_EffectInfo *effect_info = stl->effects;
   WORKBENCH_FramebufferList *fbl = vedata->fbl;
+  const WORKBENCH_PrivateData *wpd = stl->g_data;
 
   {
-    const eGPUTextureFormat hist_buffer_format = DRW_state_is_image_render() ? GPU_RGBA16F :
-                                                                               GPU_RGBA8;
+    const eGPUTextureFormat hist_buffer_format = workbench_color_texture_format(wpd);
     DRW_texture_ensure_fullscreen_2d(&txl->history_buffer_tx, hist_buffer_format, 0);
     DRW_texture_ensure_fullscreen_2d(&txl->depth_buffer_tx, GPU_DEPTH24_STENCIL8, 0);
   }
diff --git a/source/blender/draw/engines/workbench/workbench_private.h b/source/blender/draw/engines/workbench/workbench_private.h
index 17144c4dc10..cb9a97878e2 100644
--- a/source/blender/draw/engines/workbench/workbench_private.h
+++ b/source/blender/draw/engines/workbench/workbench_private.h
@@ -381,6 +381,30 @@ BLI_INLINE bool workbench_is_matdata_pass_enabled(WORKBENCH_PrivateData *wpd)
          workbench_is_in_texture_paint_mode();
 }
 
+/**
+ * Get the default texture format to be used by the color and history buffers.
+ *
+ * Use GPU_RGBA16F for final renderings and for drawing textures. This
+ * allows displaying HDRI textures. Vertex Colors uses GPU_RGBA16 to resolve
+ * color banding issues (T66100). All other modes use GPU_RGBA8 to reduce
+ * bandwidth and gpu memory.
+ */
+BLI_INLINE const eGPUTextureFormat workbench_color_texture_format(const WORKBENCH_PrivateData *wpd)
+{
+  eGPUTextureFormat result;
+  if (DRW_state_is_image_render() || workbench_is_in_texture_paint_mode() ||
+      TEXTURE_DRAWING_ENABLED(wpd)) {
+    result = GPU_RGBA16F;
+  }
+  else if (VERTEX_COLORS_ENABLED(wpd)) {
+    result = GPU_RGBA16;
+  }
+  else {
+    result = GPU_RGBA8;
+  }
+  return result;
+}
+
 /* workbench_deferred.c */
 void workbench_deferred_engine_init(WORKBENCH_Data *vedata);
 void workbench_deferred_engine_free(void);
diff --git a/source/blender/makesdna/DNA_userdef_types.h b/source/blender/makesdna/DNA_userdef_types.h
index ad3cbaeea46..f8ee29c94cc 100644
--- a/source/blender/makesdna/DNA_userdef_types.h
+++ b/source/blender/makesdna/DNA_userdef_types.h
@@ -960,6 +960,7 @@ typedef enum eUserpref_UI_Flag2 {
   USER_UIFLAG2_UNUSED_3 = (1 << 3), /* dirty */
 } eUserpref_UI_Flag2;
 
+/** #UserDef.gpu_flag */
 typedef enum eUserpref_GPU_Flag {
   USER_GPU_FLAG_NO_DEPT_PICK = (1 << 0),
   USER_GPU_FLAG_NO_EDIT_MODE_SMOOTH_WIRE = (1 << 1),