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Discussion about software development for the old-school Gameboys, ranging from the "Gray brick" to Gameboy Color
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#1 2018-11-10 23:58:14

PinoBatch
Member
Registered: 2018-03-22
Posts: 41

The first frame is always white (test ROM)

When the program turns on rendering by changing bit 7 of LCDC ($FF40) from 0 to 1, the PPU goes straight to the start of rendering (scanline 0). And for some reason, the LCD does not receive the first frame that the PPU generates, instead displaying a white screen for one frame. (On monochrome systems, this is the same whiter-than-white shade displayed when rendering is off.) Some games, such as Pokémon Pinball, use this blank frame to prepare things before turning on rendering, such as the sprite display list to be DMA copied during the first vblank.

Though recent BGB emulates this quirk, the current version of mGBA (built from Git HEAD) does not. This causes 1 frame of corruption to appear in Pokémon Pinball and numerous other games after a screen transition. Many games on KiGB's compatibility list are there because of this quirk.

So I've made a test ROM for this quirk. Expect a whiter-than-white screen on an authentic Game Boy or Game Boy Pocket, or a white screen on an authentic Game Boy Color, Game Boy Advance, or Game Boy Player. (I haven't tested it on my cousin's Super Game Boy yet.) On an emulator that does not emulate this quirk, it will instead speak truth.

Download: ROM and source zipfile

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