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core: image diff, RGBA8 pixels to the rects that differ - #667
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core.diff.Image walks two images a row at a time (identical rows cost one vectorized compare), compares differing rows per 32x32 (or 16x16) tile segment, merges changed tiles into rects and shrinks each to its exact changed pixels, with an optional per-channel tolerance and a max_rects coalesce. core.diff.TileGrid keeps 8 bytes per tile to diff a past step. std-only; bench-diff measures the DIFF_PLAN section 3 budget. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RYmfUKnG4kP4sBA4jTt5CX
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RYmfUKnG4kP4sBA4jTt5CX
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RYmfUKnG4kP4sBA4jTt5CX
…change, bench) Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01RYmfUKnG4kP4sBA4jTt5CX
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Part of fizzyedit/plans
plans/DIFF_PLAN.mdstep 3 (2.4, 3). Independent of step 1 (text):core/diff.zigis the namespace and only namesImage/TileGrid; step 1 adds its files beside them.What
core.diff.Image: stride-aware RGBA8 diff. Identical rows cost one 64-byte-vector compare (firstDiff); differing rows are compared per 32x32 (or 16x16) tile segment from the first differing byte. Changed tiles merge into rects (runs along a row, joined to an identical run above), each shrunk to its exact changed pixels (exact, default) with a pixel count. Optional per-channeltolerance,max_rectscoalescing into a bounding box,size_changedfor different sizes (overlap diffed). Shared storage and identical buffers return early. Reusable state: no allocation after the first diff of a size.core.diff.TileGrid: 8 bytes per tile (63 KB for 4K), keepable per step;diffcompares two grids into tile rects.bench-diff+ unit tests (including a property test that the rects cover every differing pixel and the pixel count is exact), rootfizzy-diff-tests.Bench (
zig build bench-diff -Doptimize=ReleaseFast, Linux cloud box)std.mem.indexOfDiff/eqlwere ~4-6x slower than the vector loop here, hencefirstDiff. Tile size default (32 vs 16) andtolerancestay open questions in the plan.SDK / UI
No SDK or plugin boundary change, no UI.
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