Fix for #36468, "Buffer Groups" option changes compositing output.

Problem is that the read/write buffer operations only work with actual
image inputs. If a singular value is used as group input no actual
buffer will be created, the write operation does not schedule any chunks
and the ReadBufferOperation subsequently returns zero
(MemoryBuffer::read).

The fix uses the (0,0) resolution to detect single value input of the
WriteBufferOperation. The actual resolution is then clamped to (1,1) to
ensure we have a single pixel to store the value in. A m_single_value
flag is also set, so we can reliably distinguish this from genuine image
resolutions without having to check m_width/m_height later on.

The ReadBufferOperation copies this flag from the associated
WriteBufferOperation and if set will always return the single value from
pixel (0,0).

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/compositor/operations/COM_WriteBufferOperation.h b/source/blender/compositor/operations/COM_WriteBufferOperation.h
index d89444045d4..157543fcb72 100644
--- a/source/blender/compositor/operations/COM_WriteBufferOperation.h
+++ b/source/blender/compositor/operations/COM_WriteBufferOperation.h
@@ -32,6 +32,7 @@
  */
 class WriteBufferOperation : public NodeOperation {
 	MemoryProxy *m_memoryProxy;
+	bool m_single_value; /* single value stored in buffer */
 	NodeOperation *m_input;
 public:
 	WriteBufferOperation();
@@ -40,11 +41,13 @@ public:
 	MemoryProxy *getMemoryProxy() { return this->m_memoryProxy; }
 	void executePixel(float output[4], float x, float y, PixelSampler sampler);
 	const bool isWriteBufferOperation() const { return true; }
+	bool isSingleValue() const { return m_single_value; }
 	
 	void executeRegion(rcti *rect, unsigned int tileNumber);
 	void initExecution();
 	void deinitExecution();
 	void executeOpenCLRegion(OpenCLDevice *device, rcti *rect, unsigned int chunkNumber, MemoryBuffer **memoryBuffers, MemoryBuffer *outputBuffer);
+	void determineResolution(unsigned int resolution[2], unsigned int preferredResolution[2]);
 	void readResolutionFromInputSocket();
 	inline NodeOperation *getInput() {
 		return m_input;