In explanation below I use 'canvas' for 'graphics':

1) image from [backcanvas] is drawn on [tmpcanvas]
2) other images are drawn on [tmpcanvas] combining with the image drawn on step 1
3) image from [tmpcanvas] is drawn on [maincanvas] with rotation
4) image from [maincanvas] is drawn on [aftermaincanvas]
5) image from [aftermaincanvas] is drawn on canvas associated with VFP form

So the image is finally "assembled" on invisible [aftermaincanvas] canvas before being drawn in a single step on VFP form -- which is a case of double buffering.

No double buffering would meant drawing all 5 steps directly on VFP form. That would produce noticeable flickering.

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I hope I did not deviate too much from the initial topic of GDI+ transparency, in which case I apologize :)