[Bf-blender-cvs] [24cc976d550] blender2.8: Workbench: Shadows: Fix corner case with degenerate triangles.

[Clément Foucault]

Commit: 24cc976d5505ee97b537742d91ae6caad04d2187
Author: Clément Foucault
Date:   Sat May 19 18:03:15 2018 +0200
Branches: blender2.8
https://developer.blender.org/rB24cc976d5505ee97b537742d91ae6caad04d2187

Workbench: Shadows: Fix corner case with degenerate triangles.

Seems that degenerate tris are somewhat widely used in modeling. So we need
to fix this. Test the edges in the geom shader since the adjacency info is
only dependant on topology, not actual vertex placement.

This fixes most of the remaining noise issues. Only a few artifacts appear
on really weird models. So if you want to get rid of the artifacts, fix
your model!

===================================================================

M	source/blender/draw/engines/workbench/shaders/workbench_shadow_geom.glsl

===================================================================

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_shadow_geom.glsl b/source/blender/draw/engines/workbench/shaders/workbench_shadow_geom.glsl
index a6cadfcfc54..baf11a2a716 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_shadow_geom.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_shadow_geom.glsl
@@ -11,6 +11,10 @@ in VertexData {
 	vec4 backPosition;
 } vData[];
 
+#define DEGENERATE_THRESHOLD 1e-12
+
+#define len_sqr(a) dot(a, a)
+
 void main()
 {
 	/* TODO precompute light_direction */
@@ -19,30 +23,51 @@ void main()
 	vec3 v10 = vData[0].pos - vData[1].pos;
 	vec3 v12 = vData[2].pos - vData[1].pos;
 	vec3 v13 = vData[3].pos - vData[1].pos;
+
+#ifdef DEGENERATE_THRESHOLD
+	vec3 v20 = vData[0].pos - vData[2].pos;
+	vec3 v23 = vData[3].pos - vData[2].pos;
+
+	vec4 edges_lensqr = vec4(len_sqr(v10), len_sqr(v13), len_sqr(v20), len_sqr(v23));
+	bvec4 degen_edges = lessThan(edges_lensqr, vec4(DEGENERATE_THRESHOLD));
+
+	/* Both triangles are degenerate, abort. */
+	if (any(degen_edges.xz) && any(degen_edges.yw))
+		return;
+#endif
+
 	vec3 n1 = cross(v12, v10);
 	vec3 n2 = cross(v13, v12);
 	vec2 facing = vec2(dot(n1, light_dir),
 	                   dot(n2, light_dir));
+
+	/* WATCH: maybe unpredictable in some cases. */
+	bool is_manifold = any(notEqual(vData[0].pos, vData[3].pos));
+
 	bvec2 backface = greaterThan(facing, vec2(0.0));
 
-	if (backface.x == backface.y) {
-		/* Both faces face the same direction. Not an outline edge. */
+#ifdef DEGENERATE_THRESHOLD
+	/* If one of the 2 triangles is degenerate, replace edge by a non-manifold one. */
+	backface.x = (any(degen_edges.xz)) ? !backface.y : backface.x;
+	backface.y = (any(degen_edges.yw)) ? !backface.x : backface.y;
+	is_manifold = (any(degen_edges)) ? false : is_manifold;
+#endif
+
+	/* If both faces face the same direction it's not an outline edge. */
+	if (backface.x == backface.y)
 		return;
-	}
 
 	/* Reverse order if backfacing the light. */
 	ivec2 idx = ivec2(1, 2);
 	idx = (backface.x) ? idx.yx : idx.xy;
 
-	/* WATCH: maybe unpredictable in some cases. */
-	bool is_manifold = any(notEqual(vData[0].pos, vData[3].pos));
-
 	gl_Position = vData[idx.x].frontPosition; EmitVertex();
 	gl_Position = vData[idx.y].frontPosition; EmitVertex();
 	gl_Position = vData[idx.x].backPosition; EmitVertex();
 	gl_Position = vData[idx.y].backPosition; EmitVertex();
 	EndPrimitive();
 
+	/* Increment/Decrement twice for manifold edges. */
 	if (is_manifold) {
 		gl_Position = vData[idx.x].frontPosition; EmitVertex();
 		gl_Position = vData[idx.y].frontPosition; EmitVertex();