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57 lines
3.0 KiB
Markdown
57 lines
3.0 KiB
Markdown
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# Radial Blur sampler optimization
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The tiled filter prepares Spin rotations or Zoom scales once per operation and
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reuses them across output tiles. Bilinear taps load all channels together, with
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specialized loops for one through five channels and a generic fallback. Rayon
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continues to parallelize output tiles on native builds.
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Draft, Good and Best keep upstream's 64, 256 and 4096 interval ceilings, sample
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positions, transparent edges and alpha arithmetic. The positive-alpha
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unpremultiply/premultiply sequence is retained to preserve floating-point rounding.
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Tests compare against the unchanged upstream sampler at large radii across
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Gray, RGB, CMYK and Lab, with and without alpha, at U8, U16 and F32 depths.
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Selection blending and unusual float alpha are covered as well.
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Only interval counts reachable within the output area are prepared; small Best
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images avoid allocating/preparing the full roughly 64 MiB transform table.
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Preparation and output allocations use checked sizes and fallible reservation.
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If the optional optimization cannot prepare its tables, the existing sampler
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runs instead. Cancellation is checked during preparation and within output tiles.
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This revision adds no source-size rejection: it retains upstream's shared
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normalized source read and therefore still requires memory proportional to source
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size. It does not claim bounded source memory or unlimited physical capacity.
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The polar approximation and background preview scheduler are separate work.
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## Local comparison (2026-10-09)
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| Method | Upstream | Optimized | Speedup | Output |
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|---|---:|---:|---:|---|
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| Spin | 66.10 s | 16.43 s | 4.02× | Exact match |
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| Zoom | 19.19 s | 5.35 s | 3.59× | Exact match |
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Baseline: current upstream sampler at main `578bc905`, through `kernel`, using
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the same shared source read, 256px output tiles, 256 MiB result batches, surface
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writeback and pruning as the tiled filter. Optimized: `apply_in`.
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The benchmark's baseline wrapper covers full-canvas, unselected filtering only;
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selection behavior is checked separately in tests.
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Machine: Intel Core i7-9750H (6 cores / 12 logical workers), Linux, Rust 1.98.1,
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release profile with opt-level 3, thin LTO and one codegen unit. Source: deterministic
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textured RGBA8 with transparent pixels, 6000×4000 (24 MP). Good quality, amount 1,
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center (0.5, 0.5), 12 Rayon workers. One paired run per method, upstream first,
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after a small untimed warmup. Entire filtering calls are timed; fixture generation
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and exact comparison of every output tile are outside the timer.
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These are single local measurements, not a cross-machine baseline or an
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amount-100 performance claim. The lower amount keeps this review benchmark
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bounded on the local laptop. Quality ceilings are verified separately at large
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radii. The example defaults to three alternating-order runs and amount 100 for
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longer measurements. Historical handoff polar/default timings do not describe
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this output-preserving implementation.
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```sh
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cargo run --release -j 12 -p photocraft-algo --example bench_radial -- 6000 4000 1 1
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```
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