Solved : I overlooked these features. I can use bmap_rendertarget to create a transparent image holding the sprite frames, then use bmap_blitpart to create the spritesheet exports.

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I am looking to create an optional .PNG export feature for my 2D animation tool, EFX. Up to 20 individual sprites can be within each frame that needs exporting.

* I am currently running into the problem that I can't use a screenshot to get the frame images because I need to keep a transparent background on the exports.
* bmap_blitpart is not working because i would need to layer a bmap with multiple effect images before moving it to a spritesheet bmap and it wont layer, only replace.
* I could make a decent one using the pixel instructions, but it wont be perfect and I'll still lose certain parts of the image thats meant to be seen behind other transparent images within the effect because the new layer of pixels will replace those under them.

Q. Is there a way that the engine background color can be rendered transparent to preserve the alpha of all the images on the screen when a png screenshot is taken?

The issue is that I'm trying to preserve the different alpha values of each sprite in the exported frames.

Have I overlooked something? What other alternative methods do I have for creating this feature?

Any help on this would be appreciated.