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Part of #449: two fingers dragged on a touch screen pan the canvas 

A pinch already zoomed the canvas and a second finger already cancelled the
first finger's press, but dragging two fingers together did nothing: the
canvas only read wheel scrolls, and a touch screen sends touches. The fingers'
movement (egui's multi-touch translation) now scrolls the canvas under either
Zoom with Mouse Wheel setting, and zoom and scroll apply in the same frame, so
a pinch that also slides pans too. Trackpads send scrolls, so nothing counts
twice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
bflatastic 2026-10-09 10:33:47 +07:00
parent 2dcac5b48b
commit 861a0759b0
2 changed files with 50 additions and 16 deletions
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2
ROADMAP.md
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64
crates/ui-egui/src/canvas.rs
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@ -516,17 +516,19 @@ fn handle_input(app: &mut VectorcraftApp, ui: &Ui, resp: &egui::Response, rect:
prev.is_some_and(|prev| prev != m)
});
// Zoom around the pointer, or scroll ([`wheel`]).
// Zoom around the pointer, and scroll ([`wheel`]): fingers pinching on a touch screen may also
// slide.
if resp.hovered() {
if (factor - 1.0).abs() > 1e-6 {
if let (Some(p), Some(vm)) = (hover, app.view_mut()) {
let before = xf.to_doc(p);
vm.zoom = (vm.zoom * factor).clamp(0.0313, 640.0);
let nx = Xf { rect, zoom: vm.zoom, center: vm.center, rot: vm.rotation.to_radians() };
let after = nx.to_doc(p);
vm.center += before - after;
}
} else if scroll != egui::Vec2::ZERO
if (factor - 1.0).abs() > 1e-6
&& let (Some(p), Some(vm)) = (hover, app.view_mut())
{
let before = xf.to_doc(p);
vm.zoom = (vm.zoom * factor).clamp(0.0313, 640.0);
let nx = Xf { rect, zoom: vm.zoom, center: vm.center, rot: vm.rotation.to_radians() };
let after = nx.to_doc(p);
vm.center += before - after;
}
if scroll != egui::Vec2::ZERO
&& let Some(vm) = app.view_mut()
{
let d = Xf { rect, zoom: vm.zoom, center: vm.center, rot: vm.rotation.to_radians() }.delta_to_doc(scroll);
@ -673,13 +675,15 @@ fn handle_input(app: &mut VectorcraftApp, ui: &Ui, resp: &egui::Response, rect:
/// How much one point of wheel motion zooms (as `exp(points × WHEEL_ZOOM)`).
const WHEEL_ZOOM: f64 = 0.01;
/// What the wheel and a pinch did over the canvas this frame: a zoom factor (about the pointer)
/// and a scroll (screen points the content moves). The wheel scrolls, Cmd- and Alt-wheel (Option
/// What the wheel, a pinch and a two-finger drag on a touch screen did over the canvas this frame:
/// a zoom factor (about the pointer) and a scroll (screen points the content moves). The wheel scrolls, Cmd- and Alt-wheel (Option
/// on the Mac) zoom. With General › Zoom with Mouse Wheel (`wheel_zooms`) the wheel and Alt-wheel
/// zoom, Shift-wheel scrolls up and down and Cmd/Ctrl-wheel sideways. `line` and `page`: points
/// per wheel line and page. `alt_turn`: the last wheel turn was an Alt-wheel one (kept by the
/// caller across frames).
fn wheel(i: &egui::InputState, wheel_zooms: bool, line: f32, page: f32, alt_turn: &mut bool) -> (f64, egui::Vec2) {
// Fingers on a touch screen pan the content with them (a trackpad sends scrolls instead).
let pan = i.multi_touch().map_or(egui::Vec2::ZERO, |t| t.translation_delta);
if !wheel_zooms {
// egui makes Cmd-wheel (and a pinch) its zoom and the rest a scroll it spreads over a few
// frames: the rest of an Alt-wheel turn zooms too, however soon Alt is let go.
@ -688,14 +692,14 @@ fn wheel(i: &egui::InputState, wheel_zooms: bool, line: f32, page: f32, alt_turn
}
let (zoom, scroll) = (f64::from(i.zoom_delta()), i.smooth_scroll_delta);
return if *alt_turn && scroll != egui::Vec2::ZERO {
(zoom * (f64::from(scroll.x + scroll.y) * WHEEL_ZOOM).exp(), egui::Vec2::ZERO)
(zoom * (f64::from(scroll.x + scroll.y) * WHEEL_ZOOM).exp(), pan)
} else {
(zoom, scroll)
(zoom, scroll + pan)
};
}
// The wheel events themselves: egui's own handling turns Cmd-wheel into a zoom.
let mut zoom = i.multi_touch().map_or(1.0, |t| f64::from(t.zoom_delta));
let mut scroll = egui::Vec2::ZERO;
let mut scroll = pan;
for e in &i.events {
match e {
egui::Event::MouseWheel { unit, delta, modifiers, .. } => {
@ -2658,6 +2662,36 @@ mod tests {
assert!((zoom - 1.0).abs() < 1e-9 && scroll.x < -1.0 && scroll.y == 0.0, "on: Cmd-wheel scrolls sideways ({zoom}, {scroll:?})");
}
/// Two fingers dragged together on a touch screen pan the canvas with them, under either
/// Zoom with Mouse Wheel setting, and draw nothing (#449).
#[test]
fn two_fingers_dragged_together_pan_the_canvas() {
for wheel_zooms in [false, true] {
let mut app = VectorcraftApp::new(Session::new(), Default::default());
app.session.execute("file.new", &json!({"width": 400, "height": 300})).unwrap();
app.session.execute("prefs.set", &json!({"key": "zoomWithMouseWheel", "value": wheel_zooms})).unwrap();
app.select_tool("rectangle");
let ctx = egui::Context::default();
frame(&mut app, &ctx, vec![]);
let c = app.canvas_rect.unwrap().center();
let touch = |n: u64, phase, pos| egui::Event::Touch { device_id: egui::TouchDeviceId(1), id: egui::TouchId(n), phase, pos, force: None };
let fingers = |phase, d: egui::Vec2| vec![touch(1, phase, c - vec2(40.0, 0.0) + d), touch(2, phase, c + vec2(40.0, 0.0) + d)];
let before = *app.view().unwrap();
// egui-winit moves the pointer with the first finger, as here.
frame(&mut app, &ctx, vec![egui::Event::PointerMoved(c - vec2(40.0, 0.0))]);
frame(&mut app, &ctx, fingers(egui::TouchPhase::Start, Vec2::ZERO));
for k in 1..=3 {
frame(&mut app, &ctx, fingers(egui::TouchPhase::Move, vec2(10.0, 8.0) * k as f32));
}
frame(&mut app, &ctx, fingers(egui::TouchPhase::End, vec2(30.0, 24.0)));
let after = *app.view().unwrap();
let moved = (after.center - before.center) * after.zoom;
assert!((after.zoom / before.zoom - 1.0).abs() < 1e-9, "no zoom: {wheel_zooms}");
assert!((moved.x + 30.0).abs() < 0.5 && (moved.y + 24.0).abs() < 0.5, "the content follows the fingers ({wheel_zooms}): {moved:?}");
assert_eq!(app.session.active().unwrap().doc.layers[0].children().unwrap().len(), 0, "nothing drawn");
}
}
#[test]
fn cmd_space_zooms_and_space_pans_whatever_the_tool() {
use egui::{Event, Modifiers};