Fix T73726: Workbench Closest Interpolation Artifacts

All textures in workbench are using linear interpolation. The fragment
shader modifies the uv coordinates to sample always in the center of a
texel. In rare conditions the GPU could sample an incorrect value due to
rounding errors making some rendering artifacts.

This patch skips the interpolation in the fragment shader to remove
these render artifacts.

Reviewed By: Clément Foucault

Differential Revision: https://developer.blender.org/D7816

1 files changed, 18 insertions, 6 deletions

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_image_lib.glsl b/source/blender/draw/engines/workbench/shaders/workbench_image_lib.glsl
index 6f99739f259..e45f7a7b9e3 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_image_lib.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_image_lib.glsl
@@ -24,11 +24,17 @@ bool node_tex_tile_lookup(inout vec3 co, sampler2DArray ima, sampler1DArray map)
 
 vec4 workbench_sample_texture(sampler2D image, vec2 coord, bool nearest_sampling)
 {
-  vec2 tex_size = vec2(textureSize(image, 0).xy);
   /* TODO(fclem) We could do the same with sampler objects.
    * But this is a quick workaround instead of messing with the GPUTexture itself. */
-  vec2 uv = nearest_sampling ? (floor(coord * tex_size) + 0.5) / tex_size : coord;
-  return texture(image, uv);
+  if (nearest_sampling) {
+    /* Use texelFetch for nearest_sampling to reduce glitches. See: T73726 */
+    vec2 tex_size = vec2(textureSize(image, 0).xy);
+    ivec2 uv = ivec2(floor(coord * tex_size) + 0.5);
+    return texelFetch(image, uv, 0);
+  }
+  else {
+    return texture(image, coord);
+  }
 }
 
 vec4 workbench_sample_texture_array(sampler2DArray tile_array,
@@ -36,7 +42,6 @@ vec4 workbench_sample_texture_array(sampler2DArray tile_array,
                                     vec2 coord,
                                     bool nearest_sampling)
 {
-  vec2 tex_size = vec2(textureSize(tile_array, 0).xy);
 
   vec3 uv = vec3(coord, 0);
   if (!node_tex_tile_lookup(uv, tile_array, tile_data))
@@ -44,8 +49,15 @@ vec4 workbench_sample_texture_array(sampler2DArray tile_array,
 
   /* TODO(fclem) We could do the same with sampler objects.
    * But this is a quick workaround instead of messing with the GPUTexture itself. */
-  uv.xy = nearest_sampling ? (floor(uv.xy * tex_size) + 0.5) / tex_size : uv.xy;
-  return texture(tile_array, uv);
+  if (nearest_sampling) {
+    /* Use texelFetch for nearest_sampling to reduce glitches. See: T73726 */
+    vec3 tex_size = vec3(textureSize(tile_array, 0));
+    uv.xy = floor(uv.xy * tex_size.xy) + 0.5;
+    return texelFetch(tile_array, ivec3(uv), 0);
+  }
+  else {
+    return texture(tile_array, uv);
+  }
 }
 
 uniform sampler2DArray imageTileArray;