845f4913cf
Co-Authored-By: selune <[email protected]> Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
48 lines
3.0 KiB
Markdown
48 lines
3.0 KiB
Markdown
# CPU texture reference sampler
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`solidcraft_render::texture_sampling` supplies the independent numerical unit in
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#1327. It does not install a texture consumer or close the wood rendering work.
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Construct `TextureView::new(rgba, [width, height])` from immutable normalized float
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RGBA. Dimensions must be positive and no larger than the existing admission edge
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limit (2048); storage is exactly `width * height * 4` floats, at most 64 MiB.
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Every channel, including alpha, must be finite and within [0, 1]. Construction
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scans once and borrows the caller's storage. Sampling does constant work without
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allocating. The sampler neither decodes nor converts color, and owns no cache.
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The normalization contribution #1267 can provide the inputs directly through
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`NormalizedTexture::rgba()` and `receipt().output_dimensions`; no normalization
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implementation or dependency is copied into this module. Raw encoded RGBA8 from
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the older admission utility is not interchangeable with normalized linear color.
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`sample_repeat_opaque([u, v])` returns three f64 channels. Both axes use periodic
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bilinear level-zero addressing. UV (0, 0) is the top-left image boundary; v grows
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downwards. Texel (x, y) is centered at ((x + 0.5) / width, (y + 0.5) / height).
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An integer coordinate lies halfway between the last and first texels. Negative
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and unwrapped coordinates repeat; nothing clamps UVs or flips rows a second time.
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Interpolation is in the supplied linear color or data space, with f64 arithmetic
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on f32 input samples. The helper applies no sRGB transfer, normal-vector decoding,
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tangent basis or engineering grain-axis interpretation. Alpha is deliberately
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ignored for this opaque API: even zero-alpha RGB participates. It must not be used
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as a transparent compositor; there is no claim of premultiplied-alpha filtering.
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Coordinates must be finite and have magnitude at most 2^20 repeats. Reduction
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precedes multiplication by dimensions. Around this bound, f64 input spacing is
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at most 2^-32 repeats, or 2^-21 texels at maximum width. Smaller sub-ULP offsets
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cannot be recovered. Tests use a 1e-9 absolute channel tolerance for analytic
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fixtures; this is not a universal error bound or f32 GPU parity certification.
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Consumers must reject or explicitly reconcile larger mapping ranges rather than
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silently clamp them. GPU upload/filtering precision requires separate evidence.
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Original generated 1x1/2x2 and rectangular constant fixtures check centers, row
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orientation, linear black/white mixing, interpolation, both seams, signed/integer
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repeats, alpha policy and hostile storage/coordinate refusal. No third-party
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assets or code are added. This invisible helper has no useful app screenshot.
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Still required for visible wood: typed bindings and persistence, local millimetre
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mapping with one inverse-instance transform, resource lifetime/budgets, product
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CPU/GPU integration, minification/mips, PNG and offline reopen evidence. Bilinear
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level-zero filtering alone does not prevent aliasing of oblique/minified grain.
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HDRI, glass, final integration and mechanical wood properties are separate work.
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