Module geometry 

D4: byte<->pixel geometry derived from a shaped run.

Relocated from the private render-wgpu ShapedRunSegmentIndex (which drew the caret + selection) and extended with the hit-test / visual-line queries the main-world editing logic needs. Deterministic: an identical ShapedRun yields an identical TextGeometry, so the value computed in the main world matches the glyphs the render world paints.

Coordinates are RUN-LOCAL logical pixels: x grows from the run’s leading edge, y (baseline_y) is the byte’s visual-line baseline offset (0 on line 1, line_idx * line_height further down). Callers add the draw origin. All byte<->x math is BiDi-correct: it splits at segment boundaries and follows visual (not logical) glyph order.

Structs

CaretGeometry

Caret placement for a logical byte, in run-local coords.

SelectionBand

One selection highlight rectangle, in run-local coords.

TextGeometry

Byte<->pixel geometry derived from one ShapedRun.