Canvas line styles & dashing #170

Phase 18: Canvas 2D API — Issue 5/10#

Implement line style properties and dashed line support for canvas stroke operations.

Dependencies#

• Canvas path API & rasterization (issue 4)

Requirements#

Line cap styles (lineCap property):

• 'butt' (default) — flat edge at endpoint
• 'round' — semicircle at endpoint
• 'square' — half-square projection at endpoint

Line join styles (lineJoin property):

• 'miter' (default) — sharp corner, clipped by miterLimit
• 'round' — circular arc at corner
• 'bevel' — flat diagonal at corner

Miter limit:

• miterLimit property (default 10.0)
• When miter length / lineWidth exceeds miterLimit, fall back to bevel join

Dash patterns:

• setLineDash(segments) — set the dash pattern (alternating dash/gap lengths)
• getLineDash() — return current dash pattern
• lineDashOffset property — offset into the dash pattern
• If segments array has odd length, double it per spec
• Empty segments array = solid line

Stroke geometry:

• Generate offset curves at ±lineWidth/2 from the path centerline
• Apply line caps at sub-path endpoints
• Apply line joins at path segment junctions
• Apply dash pattern along the path length

Acceptance criteria#

• Stroked paths respect lineCap, lineJoin, miterLimit settings
• Dashed lines render correctly with various dash patterns
• lineDashOffset shifts the dash pattern
• Round caps and joins produce visually smooth curves
• save/restore correctly preserves line style state
• Unit tests for dash pattern application and join geometry