Fix some math used by disableDepthDistance.

CesiumGS · Aug 9, 2017 · 04eb594 · 04eb594
1 parent be83a12
commit 04eb594
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Showing 2 changed files with 8 additions and 6 deletions.
diff --git a/Source/Shaders/BillboardCollectionVS.glsl b/Source/Shaders/BillboardCollectionVS.glsl
@@ -265,11 +265,12 @@ void main()
 
     if (disableDepthTestDistance != 0.0)
     {
-        gl_Position.z = min(gl_Position.z, gl_Position.w);
-
-        bool clipped = gl_Position.z < -gl_Position.w || gl_Position.z > gl_Position.w;
+        // Don't try to "multiply both sides" by w.  Greater/less-than comparisons won't work for negative values of w.
+        float zclip = gl_Position.z / gl_Position.w;
+        bool clipped = (zclip < -1.0 || zclip > 1.0);
         if (!clipped && (disableDepthTestDistance < 0.0 || (lengthSq > 0.0 && lengthSq < disableDepthTestDistance)))
         {
+            // Position z on the near plane.
             gl_Position.z = -gl_Position.w;
         }
     }

diff --git a/Source/Shaders/PointPrimitiveCollectionVS.glsl b/Source/Shaders/PointPrimitiveCollectionVS.glsl
@@ -160,11 +160,12 @@ void main()
 
     if (disableDepthTestDistance != 0.0)
     {
-        gl_Position.z = min(gl_Position.z, gl_Position.w);
-
-        bool clipped = gl_Position.z < -gl_Position.w || gl_Position.z > gl_Position.w;
+        // Don't try to "multiply both sides" by w.  Greater/less-than comparisons won't work for negative values of w.
+        float zclip = gl_Position.z / gl_Position.w;
+        bool clipped = (zclip < -1.0 || zclip > 1.0);
         if (!clipped && (disableDepthTestDistance < 0.0 || (lengthSq > 0.0 && lengthSq < disableDepthTestDistance)))
         {
+            // Position z on the near plane.
             gl_Position.z = -gl_Position.w;
         }
     }