Palette cycles + gradient modes (wrap/mirror) - #41
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Add map_brightness_rgb_cycled / map_brightness_cycled that insert a PaletteCycle remap at pass-order step 5 (between the tone curve and the gradient lookup). The public map_brightness_rgb / map_brightness keep their existing signatures and delegate with PaletteCycle::default() so all ~136 existing callers stay byte-identical. colorize_subpixel gains a trailing cycle: PaletteCycle param and routes the base color through the cored fn. frame_buffer.rs and png.rs updated with PaletteCycle::default() stubs (marked TODO(task4)) to keep the build green.
…faults Adds palette_cycle field to RenderArtDefaults (identity default for all presets), two new CLI flags (--palette-cycles N, --palette-cycle-mode MODE), a palette_cycle_mode_parsed() accessor, and extends to_render_art_defaults to override art.palette_cycle when either flag is explicitly set.
Add `palette_cycle: PaletteCycle` as a trailing param to `from_downsampled`, `from_downsampled_at`, `create_cell`, `render_colored_cell`, `png_pixel_color`, and `save_frame_as_png`. Replace all TODO(task4) stubs with the threaded value. Wire `initial_palette_cycle` from `to_render_art_defaults()` into the renderer via `set_palette_cycle` and into `RuntimeState.palette_cycle` at startup. The 256-color branch now routes through `map_brightness_cycled` for consistency. With the identity cycle (default), output is byte-identical; all 47 golden regression tests pass unchanged.
4 tasks
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Implements palette cycles (lever 6, #33): spatial palette repeat that remaps the gradient index pre-lookup so a palette tiles across the brightness range.
What
--palette-cycles <N>(1 = off, default) and--palette-cycle-mode <wrap|mirror>(mirror default).fract(t·n)(seam unless palette endpoints match)1 − |1 − fract(t·n)·2|(ping-pong, seamless on any palette)serde(default)back-compat) + per-preset render defaults via the existingRenderArtDefaultspayload.Design
map_brightness_rgb/map_brightness. The public functions keep their signatures and delegate with an identity cycle, so the ~136 UI-swatch callers are untouched; only the render chokepoints (colorize_subpixel, the 256 branch, PNG export) consume the cycle.intensity_mapping:RenderArtDefaults→RuntimeState/renderer →from_downsampled*→ colorizer, and through PNG export andsync_renderer_caches(config-load).Mechanism-only ship
Every preset defaults to identity (cycles = 1), so output is byte-identical and the 47 golden tests are unchanged. Tasteful per-preset cycle values are deferred to the showcase-presets issue (#36).
Test plan
cargo clippy --all-targets --all-features -- -D warningsclean; 819 lib + 47 golden + 19 integration pass.--preset coralbyte-identical vs dev;--palette-cycles 4 --palette-cycle-mode mirrorvisibly changes output.Closes #33.