Cut faces: the cut green for uncoloured tools, and keepMinuendColor - #173
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- An uncoloured subtrahend now paints the faces it exposes the reference's cut green (#9DCB51, what its preview shows and its colour-preserving render keeps) instead of the default geometry colour, so a cut through an uncoloured part reads as a cut. Recorded against the tool's runs before the merge; the merge looks even when every operand's colour agrees. - Evaluator::keepMinuendColor (bindings: keep_minuend_color=True) makes difference() paint cut faces with the minuend's colour instead -- the option OpenCSG cannot offer (openscad/openscad#4798). Each minuend part is differenced on its own, its cut-face runs re-minted under fresh IDs carrying that part's colour, then the parts are unioned. A union() built in this mode remembers what it merged (ColoredBody::mergedFrom, carried through transforms, color() and the cache restamp), so a union of coloured parts cuts each in its own colour. Cache keys are prefixed per mode. Off by default. BelfrySCAD #412. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Y9HJERiDZrsAb5tgmwdqU6
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Two halves of BelfrySCAD/BelfrySCAD#412's follow-up, both verified against OpenSCAD 2026.02.01.
Parity: uncoloured tools paint the cut green. The reference paints faces exposed by an uncoloured subtrahend its CGAL back-face green (#9DCB51) — in preview, and kept by its colour-preserving render (measured in a 3MF export). We painted them the default geometry yellow, so a cut through an uncoloured part could not be seen as a cut. The green is now recorded against the tool's runs before the merge, and the merge looks even when every operand's own colour agrees. A coloured tool still paints its cut with its own colour.
Evaluator::keepMinuendColor(Evaluator(keep_minuend_color=True)in the bindings):difference()paints its cut faces with the minuend's colour instead. Upstream closed the request (openscad/openscad#4798) because OpenCSG preview is pixels in a frame buffer; we do real CSG and know every triangle's provenance. Since (A ∪ B) − S = (A − S) ∪ (B − S), each minuend part is differenced on its own, its cut-face runs re-minted under fresh IDs carrying that part's colour, then the parts are unioned. Aunion()built in this mode remembers what it merged (ColoredBody::mergedFrom, carried through transforms,color()and the cache restamp), sodifference() { union() { red; blue; } tool }cuts red on the red side and blue on the blue side. Cache keys are prefixed per mode so the two never serve each other's bodies. Off by default: a viewer option, not a language feature.Tests: cut green (three cases), keep mode (single colour, per-part exact colours checked by triangle position, transform/colour carried over the union, cached union restamped with its parts, cache keyed apart), plus a bindings test. Full suite 1257/1257, bindings 42/42.
CLAUDE.mdupdated. 1.19.3 → 1.20.0.🤖 Generated with Claude Code
https://claude.ai/code/session_01Y9HJERiDZrsAb5tgmwdqU6