1 files changed, 55 insertions, 0 deletions
diff --git a/source/blender/compositor/operations/COM_ChromaMatteOperation.cc b/source/blender/compositor/operations/COM_ChromaMatteOperation.cc
index b7fec5f07e5..0784f266b19 100644
--- a/source/blender/compositor/operations/COM_ChromaMatteOperation.cc
+++ b/source/blender/compositor/operations/COM_ChromaMatteOperation.cc
@@ -29,6 +29,7 @@ ChromaMatteOperation::ChromaMatteOperation()
 
   this->m_inputImageProgram = nullptr;
   this->m_inputKeyProgram = nullptr;
+  flags.can_be_constant = true;
 }
 
 void ChromaMatteOperation::initExecution()
@@ -110,4 +111,58 @@ void ChromaMatteOperation::executePixelSampled(float output[4],
   }
 }
 
+void ChromaMatteOperation::update_memory_buffer_partial(MemoryBuffer *output,
+                                                        const rcti &area,
+                                                        Span<MemoryBuffer *> inputs)
+{
+  const float acceptance = this->m_settings->t1; /* In radians. */
+  const float cutoff = this->m_settings->t2;     /* In radians. */
+  const float gain = this->m_settings->fstrength;
+  for (BuffersIterator<float> it = output->iterate_with(inputs, area); !it.is_end(); ++it) {
+    const float *in_image = it.in(0);
+    const float *in_key = it.in(1);
+
+    /* Store matte(alpha) value in [0] to go with
+     * #COM_SetAlphaMultiplyOperation and the Value output. */
+
+    /* Algorithm from book "Video Demystified", does not include the spill reduction part. */
+    /* Find theta, the angle that the color space should be rotated based on key. */
+
+    /* Rescale to `-1.0..1.0`. */
+    // const float image_Y = (in_image[0] * 2.0f) - 1.0f;  // UNUSED
+    const float image_cb = (in_image[1] * 2.0f) - 1.0f;
+    const float image_cr = (in_image[2] * 2.0f) - 1.0f;
+
+    // const float key_Y = (in_key[0] * 2.0f) - 1.0f;  // UNUSED
+    const float key_cb = (in_key[1] * 2.0f) - 1.0f;
+    const float key_cr = (in_key[2] * 2.0f) - 1.0f;
+
+    const float theta = atan2(key_cr, key_cb);
+
+    /* Rotate the cb and cr into x/z space. */
+    const float x_angle = image_cb * cosf(theta) + image_cr * sinf(theta);
+    const float z_angle = image_cr * cosf(theta) - image_cb * sinf(theta);
+
+    /* If within the acceptance angle. */
+    /* If kfg is <0 then the pixel is outside of the key color. */
+    const float kfg = x_angle - (fabsf(z_angle) / tanf(acceptance / 2.0f));
+
+    if (kfg > 0.0f) { /* Found a pixel that is within key color. */
+      const float beta = atan2(z_angle, x_angle);
+      float alpha = 1.0f - (kfg / gain);
+
+      /* Ff beta is within the cutoff angle. */
+      if (fabsf(beta) < (cutoff / 2.0f)) {
+        alpha = 0.0f;
+      }
+
+      /* Don't make something that was more transparent less transparent. */
+      it.out[0] = alpha < in_image[3] ? alpha : in_image[3];
+    }
+    else {                     /* Pixel is outside key color. */
+      it.out[0] = in_image[3]; /* Make pixel just as transparent as it was before. */
+    }
+  }
+}
+
 }  // namespace blender::compositor