Tweens
const double x = vw::animate("panel.x", open ? 0 : -320,
{.duration = 0.45, .easing = vw::Easing::out_expo});vw::animate(id, target, options) returns the current value and moves towards target. Change the target mid-flight and it continues from where it is. While any tween is moving, the build reports animating and the surface keeps receiving frames; once all settle, frames stop.
| Option | Meaning |
|---|---|
duration |
seconds; 0 snaps (useful while a finger drags) |
initial |
starting value the first time the id is seen — initial = 0 makes things grow in |
easing |
linear, in_out_cubic, out_cubic, out_quint, out_expo, out_back, bezier, spring |
bezier |
control points {x1, y1, x2, y2} for Easing::bezier |
mass, stiffness, damping |
for Easing::spring, which keeps velocity across retargets |
min, max |
clamp the value |
A new id per occurrence restarts an animation: an entrance that should play every time a lock screen appears can use std::format("lock.intro.{}", count).
For effects that are not tweens — a pulse, a shake — call vw::request_animation_continuation() to get another frame.
Hover
input.hover = vw::Hover{.color = …, .scale = 1.02, .duration = 0.16} tints and scales a widget while the pointer is over it, without rebuilding. input.on_hover(bool inside) tells you about entering and leaving even when something is drawn on top, and the scene rebuilds afterwards — the way to open hover popouts.
Drags
.input = {
.on_drag_start = [&](const vw::DragEvent&) { dragging = true; },
.on_drag = [&](const vw::DragEvent& d) { offset = d.x - d.start_x; },
.on_drag_end = [&](const vw::DragEvent& d) {
dragging = false;
if (!d.cancelled && std::abs(offset) > width * 0.3) dismiss();
offset = 0;
}}A drag captures the pointer from the press until release, even when it leaves the widget or the scene is rebuilt underneath it. Events carry x, y, start_x, start_y, dx, dy (since the last event), button and cancelled (Escape cancels while the surface has focus). drag_button selects the mouse button (BTN_LEFT by default).
Drag rebuilds are coalesced onto frame callbacks, at most one per frame (and at least every 33 ms when the compositor sends none).