# custom-canvas-and-gestures

> Claude/Codex skill by [@zakariaf](https://omgskills.com/library/zakariaf/index.md) · 61 stars · Updated 2026-09-23

Enforces CustomPainter/Canvas discipline — the View/Painter/Scene split with a dumb painter fed one immutable Scene value type, shouldRepaint as a single value compare kept strictly separate from the AnimationController-as-repaint animation path, one shared affine transform read by BOTH painter and hit-tester (toCanvas/toLogical exact inverses, never re-derive scale), geometry hit-testing (integer lattice or rasterized region-ID buffer, never Path.contains), zero-allocation paint(), gesture-as-pure-translator emitting a typed command to a Notifier (never mutating in the handler), ExcludeSemantics + sibling Semantics speaking display values with redundant non-colour encoding, measured TextPainter fitting, first-party RoundedSuperellipseBorder, physical-pixel hairlines, and Directional-only geometry. Use when writing or reviewing a CustomPainter/CustomPaint, gestures on a canvas, tap/drag hit-testing, canvas animation, measured text fitting, or Semantics over custom-drawn pixels.

Tags: agent-skills, ai-agents, best-practices, claude-code, codex, coding-agent, cursor, dart, dartlang, developer-tools, drift, flutter, flutter-architecture, github-copilot, go-router, llm, material-design, mvvm, riverpod, skills

## Install

```sh
git clone https://github.com/zakariaf/Flutter-Skills /tmp/Flutter-Skills && ln -s /tmp/Flutter-Skills/skills/custom-canvas-and-gestures ~/.claude/skills/custom-canvas-and-gestures
```

## From README

Custom Canvas & Gestures Hand-painted surfaces (CustomPainter/Canvas) own every pixel, so they look byte-identical across platforms — but only if the painter stays dumb, the coordinate math is shared, and gestures translate rather than decide. This skill is the contract for that layer: how it splits, how pixels and pointers agree, and how a screen reader hears a canvas. Read the reference for the task at hand: references/painter-and-scene.md — the View/Painter/Scene split, the shared transform, hit-testing by geometry class, zero-allocation paint(), the two-path repaint pitfall. references/gestures-and-semantics.md — gesture-as-translator, arena arbitration, clamp-not-collision drags, custom-canvas Semantics, action/gesture parity. references/text-and-shapes.md — measured TextPainter fitting, optical centring, RoundedSuperellipseBorder, physical-pixel hairlines, concentric radii, painter-over-image-asset. Run scripts/checkpainterhygiene.sh and scripts/analyze.sh before a PR.

## Links

- HTML page: https://omgskills.com/library/zakariaf/flutter-skills/skills/custom-canvas-and-gestures/
- GitHub: https://github.com/zakariaf/Flutter-Skills
- Author: [@zakariaf](https://omgskills.com/library/zakariaf/index.md)

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