# Phase 9 Prop Editor — Round 7 (Two-Tone Halo Selection)

Status: **implemented** (2026-09-19; direct follow-up on the Round 6 selection-contrast fix).

Source: one user feedback point — the Round 6 contrast approach did not fix the reported
case.

## Diagnosis

Round 6 made the selection color adaptive to the *selected shape's fill* (dark on light
fills, white on dark fills). That solves "white shape selected on a dark canvas" but not the
reported case: a shape sitting **in front of a white shape** — the selection outline, bounding
box, rotation dot, and scale crosses extend beyond the selected shape onto the white shape
behind it, so a white (or fill-mismatched) selection still blends into the white background.
Fill-based contrast fundamentally cannot know what is behind the shape.

## Fix

Every selection element now uses a **two-tone halo**: a dark backing pass (`SELECTION_HALO_COLOR`,
black at 0.85 alpha, ~2 px wider) drawn first, then a bright core pass (`SELECTION_CORE_COLOR`,
white, the original width) on top. The pair is visible on any background — the dark halo
separates the bright core from light/white surroundings, and the bright core separates it from
dark surroundings. Applied to:

- the selection polyline over the shape outline,
- the bounding box (dark 3.5/zoom pass + white 1.5/zoom pass),
- the rotation dot (dark ring at radius + 2, white dot at radius),
- the four scale crosses (dark 3.5 pass + white 1.5 pass),
- vertex handles in Reshape mode (a 1.5 px dark ring behind each handle).

The Round 6 `contrast_color_for` helper was removed. `SELECTION_COLOR`/`GIZMO_COLOR` were
replaced by `SELECTION_CORE_COLOR`/`SELECTION_HALO_COLOR`.

## Changes

| Target | Change |
| --- | --- |
| `scripts/prop_canvas.gd` | Halo constants; two-pass drawing for selection polyline, bbox, rotation dot, scale crosses, vertex handles; `contrast_color_for` removed. |
| `tests/test_prop_editor_canvas.gd` | `_test_selection_contrast` replaced by `_test_selection_halo` (halo is dark, core is bright). |

## Verification

- `--check-only` clean; all five suites green (file 68, theme 53, canvas 100, thumb 10,
  round3 21).
- Manual F6: select a dark shape in front of a white shape, and a white shape in front of a
  white shape — the outline/box/dot/crosses must be visible in both; repeat in Reshape mode
  for the vertex handles.