Optimization Fixing a visual bug that you never saw

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Hi, I am releasing my 2d game on Steam, so sent it to review and they said it has some black and white rectangles covering parts of the screen. I don't have this issue on my old pc of course (amd 6670 vga), and I tested on a laptop too (amd gpu), without any problem. The game uses Direct3d11 with c++,  nothing fancy, 2 layer of tiles, and some sprites for decorations and some postprocess effects. I have no idea what to do. Released it a while ago on Itch.io, had some 20+ downloads, nobody said anything about not working - or anything at all, sadly. 

So anyone does have any tips, how to figure out a graphical bug that is not reproductable on your end, and you doesn't even have a screenshot?

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If you can contact the reviewers directly, ask them for system specs (DxDiag is a common approach) and screenshots.

Otherwise, you're out of luck. Unless you want to start randomly buying hardware and OSes and trying to figure out what they saw.

Bugs that can't be reproduced often wind up trashed for exactly this reason.

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Luckily a fellow dev's old geforce could repoduce the glitch, a 64x48 DXGI_FORMAT_R8_UNORM  texture caused the problem. I changed it for a DXGI_FORMAT_R8G8B8A8_UINT  type, all is good, my game is in the store now.I think the vga driver made the texture 64x64 and because my program uses only 48 lines, the lower part gets filled with some memory dump.
Actually it is pretty funny, this glitch looks someting like a C64 could do. And this game is inspired by games like Monty on the run and the time before parallax scrolling backgrounds.

- thank you for the help ApochPiQ!

Valvey glitch.png

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