Unexpected behaviour using Graphics.blit

[yngv27]

I was using it to speed up an "on the fly" italics text rendering.. and I discovered it behaves unexpectedly when the src and tgt areas overlap. I'm including a snippet you can run on the Bangle emulator to see the difference:

g.clear();
let b = Graphics.createArrayBuffer(64,24,1);
let blitArea = { w: 32, h: b.getHeight()};
g.setFontVector(12);
b.setFontVector(18);
b.drawString("ABCD1234");

g.drawString("Normal",0,8);
g.drawImage(b, 0, 20);

g.drawString("blit 'left'",0,48);
// move all pixels to the left by 8
b.blit({x1: 8, y1: 0, x2: 0, y2: 0, w: blitArea.w, h: blitArea.h});
g.drawImage(b, 0, 60);
// copies the block to the left

b.clear().drawString("ABCD1234");

g.drawString("blit 'right'",0,88);
// move all pixels to the right by 8
b.blit({x1: 0, y1: 0, x2: 8, y2: 0, w: blitArea.w, h: blitArea.h});
g.drawImage(b, 0, 100);
// repeats the first 8 bits throughout the width 

Depending on if you're shifting the graphic area to the left or right, you get different behaviour. I understand why if I consider that you are likely starting the process from lowest array offset. By the time you get to higher offsets, data has already been copied on top of the old data.. understandable. but if i had the option to perform it in the reverse order (higher offset to lower), I could accomplish what I intended (move an entire chunk of data, not repeat a pattern).

[gfwilliams]

Thanks for letting me know. If you try a cutting edge build now I think this should be fixed?

I also spotted that scrolling is effectively a blit operation, so I've swapped things around to remove a bit of code duplication there.