Grid snap (F9):
• snap spacing now tracks the visible grid zoom level — computed via
compute_grid_step() (same adaptive pow-of-5 logic as draw_grid),
updated on every ViewportMove so zooming in/out keeps snap aligned
with the grid lines on screen
Polar tracking (F10):
• configurable angle increment stored in polar_increment_deg (default 45°)
• right-click the POLAR pill to cycle through 15 → 30 → 45 → 90°
• pill label shows current angle ("POLAR 45°")
• visual guide line: while drawing with polar on, a dashed cyan line is
drawn from last_point along the snapped direction across the viewport
• SetPolarAngle message + handler; all polar_constrain() calls use the
stored increment instead of the hardcoded 45°
ROADMAP updated: Grid snap and Polar tracking marked ✅.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Before layout completes the viewport bounds are 0×0, causing project_point3
to produce NaN/Inf coordinates which panicked in lyon_path assertions.
Added early-return when bounds < 10px, and finite checks on all projected
and derived coordinates before calling any canvas drawing functions.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Screen-space UCS icon drawn on the existing selection canvas overlay.
Axes are projected from world space so the icon rotates with the camera,
always showing the correct X/Y/Z orientation relative to the drawing plane.
Each axis has its canonical color (X=red, Y=green, Z=blue) with arrowheads.
Icon visibility controlled by show_ucs_icon flag (default on); toggled by
UCSICON ON/OFF command which also updates paper-space viewport entities.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
