Wiring the first gs rule into the renderer, and it turned up a bug that had been
sitting in plain sight:
// Only mip level 0 is decoded, so minification must clamp rather than
// invent a level the disc does not have here.
ImageSamplerDescriptor {
mag_filter: ImageFilterMode::Linear,
..default() // <-- address_mode is Repeat
}
The comment describes clamping. The code was doing the opposite: `..default()`
supplies bevy's default address mode, which is ImageAddressMode::Repeat. Nothing
here ever set an address mode, so every texture was sampling with Repeat while a
comment three lines up claimed it was not.
That is the GS rule I wrote in 81ec178 saying out loud -- CLAMP, with 1.0 held at
the far edge -- and the renderer was doing the other thing. The seam shows up as a
patch running off its texture wrapping onto the opposite edge instead of repeating
the border texel, which is exactly the kind of thing that reads as "the texture
decoded wrong" and sends you looking in the format parser instead of at one line
of sampler setup.
Also set mipmap_filter to Nearest. Only level 0 is decoded, so there is no chain
to interpolate across and the filter cannot matter; Nearest is the honest setting
until levels exist, and the comment now says that gs::mip_level returns 0 for every
patch until they are decoded, rather than implying a selection is happening.
Worth noting how this was found. I went looking for where clamp01 should live and
found the answer was "somewhere that already claims to do it, and doesn't". A
comment asserting behaviour is not evidence of behaviour -- the comment here was
specific and plausible and wrong, which is worse than no comment, because it stops
anyone checking.
Two API corrections along the way, both mine: ImageSamplerDescriptor has no
`address_mode` field -- it is address_mode_u and address_mode_v separately -- and
the engine is on bevy 0.19 rather than raw wgpu, so the GS rules reach the GPU
through bevy's sampler. The roadmap now says so instead of implying a wgpu
integration that does not exist.
278 tests, clippy clean.
ReaperOfVeriod
90ec3e6adf