Thanks for the input. It would be perfect if it could compile to Mac, even if it was just a window with a canvas. I don't know if it's on your roadmap. Perhaps in a supposed cross-platform publication, it might be suggested to use crossover (like wine), but I don't know if a mse-msgui app would work this way. Mse was on my to-try sheet, maybe it's time.
Another possibility I'm thinking of is raising an OpenGL context (I think this is cross-platform), but although BGRABitmap supports OpenGL, I don't know if they would be compatible for all three platforms.
Thanks again.