1 files changed, 41 insertions, 0 deletions
diff --git a/source/blender/compositor/operations/COM_DifferenceMatteOperation.cc b/source/blender/compositor/operations/COM_DifferenceMatteOperation.cc
index 0acdfc1651f..31714b03b06 100644
--- a/source/blender/compositor/operations/COM_DifferenceMatteOperation.cc
+++ b/source/blender/compositor/operations/COM_DifferenceMatteOperation.cc
@@ -29,6 +29,7 @@ DifferenceMatteOperation::DifferenceMatteOperation()
 
   this->m_inputImage1Program = nullptr;
   this->m_inputImage2Program = nullptr;
+  flags.can_be_constant = true;
 }
 
 void DifferenceMatteOperation::initExecution()
@@ -86,4 +87,44 @@ void DifferenceMatteOperation::executePixelSampled(float output[4],
   }
 }
 
+void DifferenceMatteOperation::update_memory_buffer_partial(MemoryBuffer *output,
+                                                            const rcti &area,
+                                                            Span<MemoryBuffer *> inputs)
+{
+  for (BuffersIterator<float> it = output->iterate_with(inputs, area); !it.is_end(); ++it) {
+    const float *color1 = it.in(0);
+    const float *color2 = it.in(1);
+
+    float difference = (fabsf(color2[0] - color1[0]) + fabsf(color2[1] - color1[1]) +
+                        fabsf(color2[2] - color1[2]));
+
+    /* Average together the distances. */
+    difference = difference / 3.0f;
+
+    const float tolerance = m_settings->t1;
+    const float falloff = m_settings->t2;
+
+    /* Make 100% transparent. */
+    if (difference <= tolerance) {
+      it.out[0] = 0.0f;
+    }
+    /* In the falloff region, make partially transparent. */
+    else if (difference <= falloff + tolerance) {
+      difference = difference - tolerance;
+      const float alpha = difference / falloff;
+      /* Only change if more transparent than before. */
+      if (alpha < color1[3]) {
+        it.out[0] = alpha;
+      }
+      else { /* Leave as before. */
+        it.out[0] = color1[3];
+      }
+    }
+    else {
+      /* Foreground object. */
+      it.out[0] = color1[3];
+    }
+  }
+}
+
 }  // namespace blender::compositor