Make panels draggable on a Retina screen - #15
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Dragging a panel about the emulation canvas did nothing: the grab landed on empty canvas and the drag became a pan. `zoom` is target *pixels* per canvas pixel — what the vertex shader multiplies by — while a pointer arrives from egui in *points*, and at 2x those differ by two. Hit-testing without the conversion halved every click's distance from the top-left corner, so a panel drawn on the right of the view was tested for near the middle. The other half of the same problem: the grab was taken from where the pointer was when egui decided the press had become a drag, by which time a quick flick has left the panel it was aimed at. It now comes from press_origin, as the previz handles already do. The regression test drives the real widgets headlessly at set_pixels_per_point(2.0) — at 1x the bug does not exist, which is why the existing harness could not see it. Grab-and-drag, panning on empty canvas, and zoom-about-the-cursor are all covered now. Found by dragging panels in the app, which is the first time anyone had. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Dragging a panel about the emulation canvas did nothing — the grab landed on empty canvas and the drag became a pan. Reported from the first hands-on session with the app.
The cause.
zoomis target pixels per canvas pixel (that's what the vertex shader multiplies by), while a pointer arrives from egui in points. At 2x those differ by two, so hit-testing without the conversion halved every click's distance from the top-left corner: a panel drawn on the right of the view was tested for near the middle.The other half. The grab was taken from where the pointer was when egui decided the press had become a drag — by which time a quick flick has left the panel it was aimed at. It now comes from
press_origin, as the previz handles already do.The test. Drives the real widgets headlessly at
set_pixels_per_point(2.0). At 1x the bug does not exist, which is exactly why the existing harness could not see it — worth remembering for any egui app in the fleet. Grab-and-drag, panning on empty canvas, and zoom-about-the-cursor are all covered now; reverting the fix fails the first of them.🤖 Generated with Claude Code