Workbench: Xray: Optimize and fix implementation.

There was a method explained in the Weighted Blended Order-Independent
Transparency paper to support hardware that does not support per render
target blending function.

So now only 2 geometry passes are required instead of 3 (one being the
outline/depth fill pass).

This also fix how the blending is done. There was some premult confusion
in the implementation.

1 files changed, 14 insertions, 21 deletions

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_forward_composite_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_forward_composite_frag.glsl
index f335e1a15bd..1d9f37274bd 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_forward_composite_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_forward_composite_frag.glsl
@@ -2,9 +2,7 @@ out vec4 fragColor;
 
 uniform usampler2D objectId;
 uniform sampler2D transparentAccum;
-#ifdef WORKBENCH_REVEALAGE_ENABLED
 uniform sampler2D transparentRevealage;
-#endif
 uniform vec2 invertedViewportSize;
 
 layout(std140) uniform world_block {
@@ -16,29 +14,24 @@ void main()
 	ivec2 texel = ivec2(gl_FragCoord.xy);
 	vec2 uv_viewport = gl_FragCoord.xy * invertedViewportSize;
 	uint object_id = texelFetch(objectId, texel, 0).r;
-	vec4 transparent_accum = texelFetch(transparentAccum, texel, 0);
-#ifdef WORKBENCH_REVEALAGE_ENABLED
-	float transparent_revealage = texelFetch(transparentRevealage, texel, 0).r;
-#endif
-	vec4 color;
-	vec4 bg_color;
+
+	/* Listing 4 */
+	vec4 trans_accum = texelFetch(transparentAccum, texel, 0);
+	float trans_revealage = trans_accum.a;
+	trans_accum.a = texelFetch(transparentRevealage, texel, 0).r;
 
 #ifdef V3D_SHADING_OBJECT_OUTLINE
 	float outline = calculate_object_outline(objectId, texel, object_id);
 #else /* V3D_SHADING_OBJECT_OUTLINE */
 	float outline = 1.0;
 #endif /* V3D_SHADING_OBJECT_OUTLINE */
-	bg_color = vec4(background_color(world_data, uv_viewport.y), 0.0);
-	if (object_id == NO_OBJECT_ID) {
-		color = bg_color;
-	} else {
-#ifdef WORKBENCH_REVEALAGE_ENABLED
-		color = vec4((transparent_accum.xyz / max(transparent_accum.a, EPSILON)) * (1.0 - transparent_revealage), 1.0);
-		color = mix(bg_color, color, clamp(1.0 - transparent_revealage, 0.0, 1.0));
-#else
-		color = vec4(transparent_accum.xyz / max(transparent_accum.a, EPSILON), 1.0);
-#endif
-	}
-
-	fragColor = vec4(mix(world_data.object_outline_color.rgb, color.xyz, outline), 1.0);
+	vec3 bg_color = background_color(world_data, uv_viewport.y);
+
+	/* TODO: Bypass the whole shader if there is no xray pass and no outline pass. */
+	vec3 trans_color = trans_accum.rgb / clamp(trans_accum.a, 1e-4, 5e4);
+	vec3 color = mix(trans_color, bg_color, trans_revealage);
+
+	color = mix(world_data.object_outline_color.rgb, color, outline);
+
+	fragColor = vec4(color, 1.0);
 }