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Remove scroll latency for smooth trackpads #4526

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merged 1 commit into from
May 23, 2024
Merged

Remove scroll latency for smooth trackpads #4526

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49 changes: 32 additions & 17 deletions crates/egui/src/input_state.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -199,8 +199,11 @@ impl InputState {
let pointer = self.pointer.begin_frame(time, &new);

let mut keys_down = self.keys_down;
let mut zoom_factor_delta = 1.0; // TODO(emilk): smoothing for zoom factor
let mut raw_scroll_delta = Vec2::ZERO;
let mut zoom_factor_delta = 1.0;
let mut unprocessed_scroll_delta = self.unprocessed_scroll_delta;
let mut smooth_scroll_delta = Vec2::ZERO;

for event in &mut new.events {
match event {
Event::Key {
Expand All @@ -221,7 +224,7 @@ impl InputState {
delta,
modifiers,
} => {
let delta = match unit {
let mut delta = match unit {
MouseWheelUnit::Point => *delta,
MouseWheelUnit::Line => {
// TODO(emilk): figure out why these constants need to be different on web and on native (winit).
Expand All @@ -236,16 +239,35 @@ impl InputState {
}
MouseWheelUnit::Page => screen_rect.height() * *delta,
};

if modifiers.ctrl || modifiers.command {
// Treat as zoom instead:
let factor = (delta.y / 200.0).exp();
zoom_factor_delta *= factor;
} else if modifiers.shift {
// Treat as horizontal scrolling.
// Note: one Mac we already get horizontal scroll events when shift is down.
raw_scroll_delta.x += delta.x + delta.y;
} else {
if modifiers.shift {
// Treat as horizontal scrolling.
// Note: one Mac we already get horizontal scroll events when shift is down.
delta = vec2(delta.x + delta.y, 0.0);
}

raw_scroll_delta += delta;

// Mouse wheels often go very large steps.
// A single notch on a logitech mouse wheel connected to a Macbook returns 14.0 raw_scroll_delta.
// So we smooth it out over several frames for a nicer user experience when scrolling in egui.
// BUT: if the user is using a nice smooth mac trackpad, we don't add smoothing,
// because it adds latency.
let is_smooth = match unit {
MouseWheelUnit::Point => delta.length() < 5.0, // a bit arbitrary here
MouseWheelUnit::Line | MouseWheelUnit::Page => false,
};

if is_smooth {
smooth_scroll_delta += delta;
} else {
unprocessed_scroll_delta += delta;
}
}
}
Event::Zoom(factor) => {
Expand All @@ -255,25 +277,18 @@ impl InputState {
}
}

let mut unprocessed_scroll_delta = self.unprocessed_scroll_delta;

let mut smooth_scroll_delta = Vec2::ZERO;

{
// Mouse wheels often go very large steps.
// A single notch on a logitech mouse wheel connected to a Macbook returns 14.0 raw_scroll_delta.
// So we smooth it out over several frames for a nicer user experience when scrolling in egui.
unprocessed_scroll_delta += raw_scroll_delta;
let dt = stable_dt.at_most(0.1);
let t = crate::emath::exponential_smooth_factor(0.90, 0.1, dt); // reach _% in _ seconds. TODO(emilk): parameterize

for d in 0..2 {
if unprocessed_scroll_delta[d].abs() < 1.0 {
smooth_scroll_delta[d] = unprocessed_scroll_delta[d];
smooth_scroll_delta[d] += unprocessed_scroll_delta[d];
unprocessed_scroll_delta[d] = 0.0;
} else {
smooth_scroll_delta[d] = t * unprocessed_scroll_delta[d];
unprocessed_scroll_delta[d] -= smooth_scroll_delta[d];
let applied = t * unprocessed_scroll_delta[d];
smooth_scroll_delta[d] += applied;
unprocessed_scroll_delta[d] -= applied;
}
}
}
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