fix(measurement-tool): apply devicePixelRatio in legacy applyToolTran…#229
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sebcarley wants to merge 1 commit into
Open
fix(measurement-tool): apply devicePixelRatio in legacy applyToolTran…#229sebcarley wants to merge 1 commit into
sebcarley wants to merge 1 commit into
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…sform On Retina (HiDPI) displays the in-progress measurement preview was drawn at half size and anchored to the page origin instead of tracking the cursor. The page is rendered at scale * devicePixelRatio, but the legacy branch of applyToolTransform only applied scale, dropping the DPR factor. The header comment notes 'DPR handled elsewhere' for legacy mode, but in this code path it wasn't. Use ctx.setTransform with scale * dpr so the legacy branch matches the page render transform. Switched from ctx.scale to ctx.setTransform for symmetry with the vector-viewport branch above; at identity-canvas state the two are equivalent, so other tools that call applyToolTransform are unaffected. Verified on macOS 26.4.1, Apple Silicon, devicePixelRatio=2. Affects: area and perimeter measurement tools (any tool calling applyToolTransform after ctx.redraw()).
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Summary
On Retina (HiDPI) displays, the in-progress measurement preview is drawn at half size and anchored to the page origin instead of tracking the cursor. The final shape (after Enter) draws correctly. Affects area and perimeter measurement tools.
Root cause
In js/tools/tool-context.js, applyToolTransform has two branches. The vector-viewport branch correctly uses setTransform with the active viewport zoom. The legacy branch uses:
jsconst scale = doc?.scale || 1.5;
ctx.scale(scale, scale);
But the page itself is rendered at scale * devicePixelRatio (DPR=2 on Retina). The preview transform drops the DPR factor, so the preview lands at half size from origin (0,0).
The function's header comment notes "DPR handled elsewhere" for legacy mode, but in the preview-drawing call path it isn't.
I confirmed via dev-console logging that when applyToolTransform runs from _measureMultiClickMove, the canvas is at the identity transform — the function is correctly being called from a clean state, just applying the wrong total transform.
Fix
jsconst dpr = window.devicePixelRatio || 1;
ctx.setTransform(scale * dpr, 0, 0, scale * dpr, 0, 0);
Switched from ctx.scale() to ctx.setTransform() for symmetry with the vector-viewport branch above. At identity-canvas state the two are equivalent, so other tools that call applyToolTransform (angle, draw, spline, calibration-pick, arc, select) are unaffected — verified all still working.
Testing
macOS 26.4.1, Apple Silicon, devicePixelRatio = 2
Built from main (v1.46.0)
Confirmed area and perimeter previews now track the cursor at the correct scale and position, at all zoom levels
Confirmed other tools (angle, draw, calibration) still render correctly
Notes
I'm a non-developer who hit this bug while building from source for personal use. Happy to make any changes you'd like, or if you'd prefer to handle it differently, feel free to close this and I'll learn from whatever you ship.