My old code to display Spectrum 512 images within STOS. Routine works by installing onto the VBL interupt, which means it returns you back to STOS so you can do some other stuff.
If I remember rightly you could get some very simple sprites etc, music playing sort of thing, but the majority of the CPU time is taken by the display routine.
Included is the source code for the display routine as well as the STOS source to use it.
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