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TimeOfDeath

why is this a visplane overflow?

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wad: visplane.wad (e1m1)

The visplane overflow is a fatal error that occurs in vanilla Doom when there are more than 128 unique floor and ceiling surfaces (visplanes) on the screen simultaneously.

But the map only has 14 sectors.

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Press F6 and it'll show you exactly where visplanes are getting split, so you can get a better idea of what sorts of structures are likely to cause splits.

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The 128 combinations explanation is overly simplistic -- Doom has to split visplanes when they don't share contiguous regions (I am a bit rusty on the exact nature of how they have to be contiguous in order for the same plane to be reused, though).

Lee Killough's infamous VPO test level only consists of two sectors, but they are divided up into a huge chess board. This interleaving of different properties causes the engine to use several thousand visplanes where, if the idealistic simplistic explanation of "unique combinations" were the only restriction in effect, it would use 2.

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Thanks for the replies, managed to get the visplanes below 100.

Also, a different topic: why do switch textures used as middle textures crash the game?

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Doom's renderer isn't programmed to draw midtextures with multiple patches, basically. It can draw them only if the patches are arranged horizontally and not overlapping (i.e. two 64x128 patches beside each other is fine, but two 128x64 patches stacked above and below each other is not).

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