Dissolve blending mode. The category should be changed, I don't know about the compositor categories so I just left it at "compositors:math". I tried to follow the way GIMP's dissolve works but gegl is obviously different. There's no mask or opacity input like in GIMP, I assume masking or gegl:opacity is already done on the inputs. Tell me if I need to change something or add those properties.
Attachment:
dissolve.c
Description: Text Data