frederic-mahe / Analogue-Pocket

An issue tracker for Analogue's Pocket, a handheld FPGA device released in December 2021
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Graphical glitch vs MGB/CGB/AGS101/GBBC/etc on homebrew demo #54

Open bbbbbr opened 2 years ago

bbbbbr commented 2 years ago

Tested with firmware: 1.0, 1.0a Present in: GBC mode, Force GB mode

When running the torch effect demo on the Analogue Pocket (AP) there's a glitch on the left-edge of the screen. The background hardware map swap is taking visual effect about 8 pixels too soon compared with actual hardware. This causes it to show the background scrolling variation that's normally hidden under the left edge sprites.

I haven't tried to diagnose it, but possible there could be issues with the timing where it syncs before entering the scanline loop, or perhaps timing with when exactly it calls the ISR for the LYC interrupt.

ROM: https://github.com/bbbbbr/gb-torch-effect/blob/release_1.0/bin/torch.gb

Source: https://github.com/bbbbbr/gb-torch-effect

Attached are reference videos of normal behavior on other hardware (including GBBoy Colour).

AP_torch_demo_glitch

https://user-images.githubusercontent.com/8322401/151752077-f8b71d66-427a-4de6-8081-622cbd89ea94.mp4

https://user-images.githubusercontent.com/8322401/151752085-499e2a5b-c8ac-4582-b36b-c96af1c08702.mp4

https://user-images.githubusercontent.com/8322401/151752087-fb01b742-5048-4da5-8c06-f2e3a155aaaf.mp4

https://user-images.githubusercontent.com/8322401/151752100-0b223474-c838-4cf9-8630-faa156674259.mp4