1 files changed, 36 insertions, 0 deletions
diff --git a/source/blender/compositor/operations/COM_LuminanceMatteOperation.cc b/source/blender/compositor/operations/COM_LuminanceMatteOperation.cc
index 5ca16e40ce3..c642c60b912 100644
--- a/source/blender/compositor/operations/COM_LuminanceMatteOperation.cc
+++ b/source/blender/compositor/operations/COM_LuminanceMatteOperation.cc
@@ -29,6 +29,7 @@ LuminanceMatteOperation::LuminanceMatteOperation()
   addOutputSocket(DataType::Value);
 
   this->m_inputImageProgram = nullptr;
+  flags.can_be_constant = true;
 }
 
 void LuminanceMatteOperation::initExecution()
@@ -78,4 +79,39 @@ void LuminanceMatteOperation::executePixelSampled(float output[4],
   output[0] = min_ff(alpha, inColor[3]);
 }
 
+void LuminanceMatteOperation::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 *color = it.in(0);
+    const float luminance = IMB_colormanagement_get_luminance(color);
+
+    /* One line thread-friend algorithm:
+     * `it.out[0] = MIN2(color[3], MIN2(1.0f, MAX2(0.0f, ((luminance - low) / (high - low))));`
+     */
+
+    /* Test range. */
+    const float high = m_settings->t1;
+    const float low = m_settings->t2;
+    float alpha;
+    if (luminance > high) {
+      alpha = 1.0f;
+    }
+    else if (luminance < low) {
+      alpha = 0.0f;
+    }
+    else { /* Blend. */
+      alpha = (luminance - low) / (high - low);
+    }
+
+    /* Store matte(alpha) value in [0] to go with
+     * COM_SetAlphaMultiplyOperation and the Value output.
+     */
+
+    /* Don't make something that was more transparent less transparent. */
+    it.out[0] = MIN2(alpha, color[3]);
+  }
+}
+
 }  // namespace blender::compositor