> For example can the canvas grab everything below it, including other effects.
Yep, and this is what Davioware meant, for fullscreen effect processing. You want to set it to grab the layout before drawing (it means "grab layout before drawing the canvas"). That means it works like this:
Layout (everything beneath the canvas) is fully drawn
Canvas takes a snapshot of that
Canvas processes an effect (assuming you added one) and draws on top of everything
End result: you see everything with an effect applied.
'Grab after drawing' means it takes a snapshot after the canvas has already drawn itself. That's useful for frame feedback effects, such as an effect mixing the previous frame and the current frame (usually the canvas has to be semitransparent for that to work).
Yep got back a few minutes ago and gave it a try soon as I sat down, worked perfectly! I'm using that bloom effect you posted way back actually, the blur horizontal x2 / vertical x2 + glow. Looks really nice. Plus having it on it's own layer makes adding options to turn the effect on and off, really simple.
I also noticed the canvas bug where using different size canvases with a pre-drawn texture ends up with it removing entire chunks of it, doesn't happen at all when grabbing the layout. So making a canvas of only 8x8 and stretching it to fill the entire display works great! Doesn't effect the quality at all, but runs much faster and uses barely any extra VRAM!