For example, I want to deform the red-blue shape to fit the gray triangle underneath, they are located on different layers. But when I use Q’MIC, I can only see the selected layer. Is there a way to add an additional layer or image as a reference?
Yes, there should be drop down option. Now, for the deform using a image, that’d require a interactive filter that can use multiple layere. I’d say you’re better off with a program that lets you do that.