Fix T39799: Backdrop (compositor) ignores alpha.

This issue is because of a somewhat "special" behavior in old code, which got lost during rB09874df:

There was a variant of the `relinkConnections` function which would leave the socket completely unconnected. This is not a valid state really (given that each unconnected input must otherwise connected to a constant `Set` type node), but was used as a way to distinguish connected alpha/depth sockets in composite and viewer output nodes.
https://developer.blender.org/diffusion/B/browse/master/source/blender/compositor/intern/COM_InputSocket.cpp;28a829893c702918afc5ac1945a06eaefa611594$69

After the large cleanup patch ({D309}) every socket is now automatically connected to a constant, such that `getInputSocketReader` will never return a NULL pointer. This breaks the previous test method, which needs to be replaced by more explicit flags. Luckily this was done only for very few output nodes (Composite, Viewer, Output-File). These now use the regular SetValueOperation default in case "use alpha" is disabled, but set this to an explicit 1.0 value instead of mapping to the node socket.

1 files changed, 2 insertions, 1 deletions

diff --git a/source/blender/compositor/nodes/COM_OutputFileNode.cpp b/source/blender/compositor/nodes/COM_OutputFileNode.cpp
index 83b138c1b07..92fa74b9a2e 100644
--- a/source/blender/compositor/nodes/COM_OutputFileNode.cpp
+++ b/source/blender/compositor/nodes/COM_OutputFileNode.cpp
@@ -56,7 +56,8 @@ void OutputFileNode::convertToOperations(NodeConverter &converter, const Composi
 			NodeInput *input = getInputSocket(i);
 			NodeImageMultiFileSocket *sockdata = (NodeImageMultiFileSocket *)input->getbNodeSocket()->storage;
 			
-			outputOperation->add_layer(sockdata->layer, input->getDataType());
+			/* note: layer becomes an empty placeholder if the input is not linked */
+			outputOperation->add_layer(sockdata->layer, input->getDataType(), input->isLinked());
 			
 			converter.mapInputSocket(input, outputOperation->getInputSocket(i));