Add check for degenerate sub-triangles in OcclusionBuffer::DrawTriangle2D. Fixes #2322.

Source/Urho3D/Graphics/OcclusionBuffer.cpp

@@ -879,103 +879,120 @@ void OcclusionBuffer::DrawTriangle2D(const Vector3* vertices, bool clockwise, un
     if (!clockwise)
         middleIsRight = !middleIsRight;
 
+    const bool topDegenerate = topY == middleY;
+    const bool bottomDegenerate = middleY == bottomY;
+
     Gradients gradients(vertices);
-    Edge topToMiddle(gradients, vertices[top], vertices[middle], topY);
     Edge topToBottom(gradients, vertices[top], vertices[bottom], topY);
-    Edge middleToBottom(gradients, vertices[middle], vertices[bottom], middleY);
 
     int* bufferData = buffers_[threadIndex].data_;
 
     if (middleIsRight)
     {
         // Top half
-        int* row = bufferData + topY * width_;
-        int* endRow = bufferData + middleY * width_;
-        while (row < endRow)
+        if (!topDegenerate)
         {
-            int invZ = topToBottom.invZ_;
-            int* dest = row + (topToBottom.x_ >> 16u);
-            int* end = row + (topToMiddle.x_ >> 16u);
-            while (dest < end)
+            Edge topToMiddle(gradients, vertices[top], vertices[middle], topY);
+            int* row = bufferData + topY * width_;
+            int* endRow = bufferData + middleY * width_;
+            while (row < endRow)
             {
-                if (invZ < *dest)
-                    *dest = invZ;
-                invZ += gradients.dInvZdXInt_;
-                ++dest;
-            }
+                int invZ = topToBottom.invZ_;
+                int* dest = row + (topToBottom.x_ >> 16u);
+                int* end = row + (topToMiddle.x_ >> 16u);
+                while (dest < end)
+                {
+                    if (invZ < *dest)
+                        *dest = invZ;
+                    invZ += gradients.dInvZdXInt_;
+                    ++dest;
+                }
 
-            topToBottom.x_ += topToBottom.xStep_;
-            topToBottom.invZ_ += topToBottom.invZStep_;
-            topToMiddle.x_ += topToMiddle.xStep_;
-            row += width_;
+                topToBottom.x_ += topToBottom.xStep_;
+                topToBottom.invZ_ += topToBottom.invZStep_;
+                topToMiddle.x_ += topToMiddle.xStep_;
+                row += width_;
+            }
         }
 
         // Bottom half
-        row = bufferData + middleY * width_;
-        endRow = bufferData + bottomY * width_;
-        while (row < endRow)
+        if (!bottomDegenerate)
         {
-            int invZ = topToBottom.invZ_;
-            int* dest = row + (topToBottom.x_ >> 16u);
-            int* end = row + (middleToBottom.x_ >> 16u);
-            while (dest < end)
+            Edge middleToBottom(gradients, vertices[middle], vertices[bottom], middleY);
+            int* row = bufferData + middleY * width_;
+            int* endRow = bufferData + bottomY * width_;
+            while (row < endRow)
             {
-                if (invZ < *dest)
-                    *dest = invZ;
-                invZ += gradients.dInvZdXInt_;
-                ++dest;
-            }
+                int invZ = topToBottom.invZ_;
+                int* dest = row + (topToBottom.x_ >> 16u);
+                int* end = row + (middleToBottom.x_ >> 16u);
+                while (dest < end)
+                {
+                    if (invZ < *dest)
+                        *dest = invZ;
+                    invZ += gradients.dInvZdXInt_;
+                    ++dest;
+                }
 
-            topToBottom.x_ += topToBottom.xStep_;
-            topToBottom.invZ_ += topToBottom.invZStep_;
-            middleToBottom.x_ += middleToBottom.xStep_;
-            row += width_;
+                topToBottom.x_ += topToBottom.xStep_;
+                topToBottom.invZ_ += topToBottom.invZStep_;
+                middleToBottom.x_ += middleToBottom.xStep_;
+                row += width_;
+            }
         }
     }
     else
     {
         // Top half
-        int* row = bufferData + topY * width_;
-        int* endRow = bufferData + middleY * width_;
-        while (row < endRow)
+        if (!topDegenerate)
         {
-            int invZ = topToMiddle.invZ_;
-            int* dest = row + (topToMiddle.x_ >> 16u);
-            int* end = row + (topToBottom.x_ >> 16u);
-            while (dest < end)
+            Edge topToMiddle(gradients, vertices[top], vertices[middle], topY);
+            int* row = bufferData + topY * width_;
+            int* endRow = bufferData + middleY * width_;
+            while (row < endRow)
             {
-                if (invZ < *dest)
-                    *dest = invZ;
-                invZ += gradients.dInvZdXInt_;
-                ++dest;
-            }
+                int invZ = topToMiddle.invZ_;
+                int* dest = row + (topToMiddle.x_ >> 16u);
+                int* end = row + (topToBottom.x_ >> 16u);
+                while (dest < end)
+                {
+                    if (invZ < *dest)
+                        *dest = invZ;
+                    invZ += gradients.dInvZdXInt_;
+                    ++dest;
+                }
 
-            topToMiddle.x_ += topToMiddle.xStep_;
-            topToMiddle.invZ_ += topToMiddle.invZStep_;
-            topToBottom.x_ += topToBottom.xStep_;
-            row += width_;
+                topToMiddle.x_ += topToMiddle.xStep_;
+                topToMiddle.invZ_ += topToMiddle.invZStep_;
+                topToBottom.x_ += topToBottom.xStep_;
+                row += width_;
+            }
         }
 
         // Bottom half
-        row = bufferData + middleY * width_;
-        endRow = bufferData + bottomY * width_;
-        while (row < endRow)
+        if (!bottomDegenerate)
         {
-            int invZ = middleToBottom.invZ_;
-            int* dest = row + (middleToBottom.x_ >> 16u);
-            int* end = row + (topToBottom.x_ >> 16u);
-            while (dest < end)
+            Edge middleToBottom(gradients, vertices[middle], vertices[bottom], middleY);
+            int* row = bufferData + middleY * width_;
+            int* endRow = bufferData + bottomY * width_;
+            while (row < endRow)
             {
-                if (invZ < *dest)
-                    *dest = invZ;
-                invZ += gradients.dInvZdXInt_;
-                ++dest;
-            }
+                int invZ = middleToBottom.invZ_;
+                int* dest = row + (middleToBottom.x_ >> 16u);
+                int* end = row + (topToBottom.x_ >> 16u);
+                while (dest < end)
+                {
+                    if (invZ < *dest)
+                        *dest = invZ;
+                    invZ += gradients.dInvZdXInt_;
+                    ++dest;
+                }
 
-            middleToBottom.x_ += middleToBottom.xStep_;
-            middleToBottom.invZ_ += middleToBottom.invZStep_;
-            topToBottom.x_ += topToBottom.xStep_;
-            row += width_;
+                middleToBottom.x_ += middleToBottom.xStep_;
+                middleToBottom.invZ_ += middleToBottom.invZStep_;
+                topToBottom.x_ += topToBottom.xStep_;
+                row += width_;
+            }
         }
     }
 }