If any gfx people following me happen to know, a question I've had for a long time: why is the native MIP UV comp still the way it is? It seems like it's a bad way to do MIPs, because it doesn't work with borders or tiling. Why isn't the default like https://pages.jh.edu/dighamm/research/2004_01_sta.pdf …?
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I feel like I must be missing something, but I don't know. Maybe the answer is that MIP UVs aren't accelerated in hardware in any special way anymore, and it's always done in the shader anyway, so it's "free" to do your own sampling of this nature?
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Replying to @cmuratori
Texels are processed by 2x2 quads, so my guess is that using uv derivatives to compute mip level per-quad this way is very cheap if not free and just works in most cases.
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Replying to @benoitvimont
The MIP UV specification I referenced does not change that. It is strictly a scale+bias of the UVs per MIP level. The derivatives are calculated precisely as before.
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Replying to @cmuratori @benoitvimont
its not quite tho? as the scale has to be towards the center of each chart, ie the bias depends in some complex way on where you are in the overall atlas… still, i would love it too :)
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Replying to @mmalex @benoitvimont
Just to be clear, I don't mean atlases. There are atlases in the paper but also a texture array alternative, which is what I meant. And it seems like it's the way you would normally want to do MIP'ing, because it allows borders and tiling.
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Replying to @cmuratori @benoitvimont
ah fair enough. i assumed you meant atlases. my bad.
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Replying to @mmalex @benoitvimont
I haven't studied the atlas version so it may also "just work" but the one where it's just a single texture was very eye-opening. By considering the border to be one texel around, and adjusting MIPs accordingly, you get seamless tiling and/or proper borders.
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And I was trying to figure out why this isn't the new standard way to do MIPs - it seems like you would always want this. Regular MIPs don't work very well, because they don't tile, so they always produce seams...
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Replying to @cmuratori @benoitvimont
yeah i did a double take reading it because at first i thought it was referring to a single texel - ie a border color! - but that was just my bias due to how i thought hw worked. i had no idea we ever had a ‘1 texel round’ mode…
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