Fix T50849: Transparent background produces artifacts in this compositing setup

The issue was caused by sometimes negative color returned by the filter node.

Seems to be caused by precision issues. Don't see any reason why we would want
negative colors in output. Those only causing issues later on.

2 files changed, 12 insertions, 0 deletions

diff --git a/source/blender/compositor/operations/COM_ConvolutionEdgeFilterOperation.cpp b/source/blender/compositor/operations/COM_ConvolutionEdgeFilterOperation.cpp
index e1ada9a8c39..5f78067220a 100644
--- a/source/blender/compositor/operations/COM_ConvolutionEdgeFilterOperation.cpp
+++ b/source/blender/compositor/operations/COM_ConvolutionEdgeFilterOperation.cpp
@@ -94,4 +94,10 @@ void ConvolutionEdgeFilterOperation::executePixel(float output[4], int x, int y,
 	output[2] = output[2] * value[0] + in2[2] * mval;
 	
 	output[3] = in2[3];
+
+	/* Make sure we don't return negative color. */
+	output[0] = max(output[0], 0.0f);
+	output[1] = max(output[1], 0.0f);
+	output[2] = max(output[2], 0.0f);
+	output[3] = max(output[3], 0.0f);
 }
diff --git a/source/blender/compositor/operations/COM_ConvolutionFilterOperation.cpp b/source/blender/compositor/operations/COM_ConvolutionFilterOperation.cpp
index 68ec2be5ebd..6ac1ff9a1eb 100644
--- a/source/blender/compositor/operations/COM_ConvolutionFilterOperation.cpp
+++ b/source/blender/compositor/operations/COM_ConvolutionFilterOperation.cpp
@@ -107,6 +107,12 @@ void ConvolutionFilterOperation::executePixel(float output[4], int x, int y, voi
 	output[1] = output[1] * value[0] + in2[1] * mval;
 	output[2] = output[2] * value[0] + in2[2] * mval;
 	output[3] = output[3] * value[0] + in2[3] * mval;
+
+	/* Make sure we don't return negative color. */
+	output[0] = max(output[0], 0.0f);
+	output[1] = max(output[1], 0.0f);
+	output[2] = max(output[2], 0.0f);
+	output[3] = max(output[3], 0.0f);
 }
 
 bool ConvolutionFilterOperation::determineDependingAreaOfInterest(rcti *input, ReadBufferOperation *readOperation, rcti *output)