New pure functions for the canvas viewport (v4.13.0):
- zoomAt(view, screenX, screenY, factor) — zoom centred on a screen
point, keeping the world point under cursor fixed. Clamped to
[0.25, 4] scale range.
- panBy(view, dx, dy) — additive pan
- reset() — identity transform
- wheelFactor(deltaY) — multiplicative factor per Ctrl+wheel notch
- snap(value, gridSize) — round to nearest grid (0 disables)
The actual SVG transform wrapper + Ctrl+wheel handler + drag-to-pan
+ snap-on-move is the next canvas-layer commit; this commit lands
the testable math.
14 new tests cover: identity reset, cursor-stable zoom, MIN/MAX
clamping, additive pan, wheel factor reciprocity, snap-to-grid
(positive/negative/zero grid sizes).
Amit Haridas
