Bug 786992 - removing alpha produces a black image (sometimes), with OpenCL
When creating a flatten node, which is used when removing alpha channels and when flattening an image, use a gimp:normal node to combine the layer with the background color, instead of a gegl:over node. gegl:over can apparently result in completely black output with OpenCL enabled, under certain (not fully pinned-down) conditions. As long as the OpenCL version of gegl:over is borked, there is not much reason to use it over gimp:normal, which is more consistent (in intension, if not in extension) with the rest of the compositing pipeline.
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