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, 15 insertions, 0 deletions

diff --git a/source/blender/compositor/operations/COM_WriteBufferOperation.cpp b/source/blender/compositor/operations/COM_WriteBufferOperation.cpp
index 17c8f4d9fd1..f18493dc334 100644
--- a/source/blender/compositor/operations/COM_WriteBufferOperation.cpp
+++ b/source/blender/compositor/operations/COM_WriteBufferOperation.cpp
@@ -174,6 +174,21 @@ void WriteBufferOperation::executeOpenCLRegion(OpenCLDevice *device, rcti *rect,
 	delete clKernelsToCleanUp;
 }
 
+void WriteBufferOperation::determineResolution(unsigned int resolution[2], unsigned int preferredResolution[2])
+{
+	NodeOperation::determineResolution(resolution, preferredResolution);
+	/* make sure there is at least one pixel stored in case the input is a single value */
+	m_single_value = false;
+	if (resolution[0] == 0) {
+		resolution[0] = 1;
+		m_single_value = true;
+	}
+	if (resolution[1] == 0) {
+		resolution[1] = 1;
+		m_single_value = true;
+	}
+}
+
 void WriteBufferOperation::readResolutionFromInputSocket()
 {
 	NodeOperation *inputOperation = this->getInputOperation(0);