InteractiveViewer
InteractiveViewer gives one retained child a runtime-owned two-dimensional camera. It is the low-level choice for maps, diagrams, image inspection, and other surfaces that need pan and uniform zoom without adopting the node-and-edge model of InfiniteCanvas.
The widget is available with the desktop, android, ios, mobile, and web Fission features. It is intentionally absent from Static site, SSR, and Terminal-only builds.
Example
use fission::prelude::*;
let viewer: Widget = InteractiveViewer {
id: Some(WidgetId::explicit("document-viewport")),
child: Image::asset("floor-plan.png").into(),
min_scale: 0.25,
max_scale: 8.0,
pan_axis: ViewportPanAxis::Both,
zoom_policy: ViewportZoomPolicy::WheelWithModifier,
..Default::default()
}
.into();
With transform: None, Fission owns transient pan, pinch, magnification, wheel, and inertial state. Set transform: Some(...) when application state is authoritative. initial_transform only seeds an uncontrolled viewer.
Interaction callbacks
The on_interaction_start, on_interaction_update, and on_interaction_end envelopes keep their bound payload. Live camera facts arrive separately through ctx.input.viewport_interaction():
•
target WidgetId and lifecycle phase;
•
complete ViewportTransform;
•
viewport and world focal points;
•
pan delta and multiplicative scale factor;
•
input family and active modifiers.
This lets one reducer bind stable document context without encoding runtime coordinates into its action value.
Behavior
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A single primary pointer pans after the movement threshold.
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Two contacts pan and pinch around their centroid. Adding a second contact cancels a pending child tap or drag and captures the nearest viewer.
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Releasing one of two contacts resets the baseline, avoiding a camera jump.
•
macOS magnification gestures and Web browser pinch gestures zoom around their focal point.
•
Modifier-wheel zoom and unmodified wheel pan follow zoom_policy and pan_axis.
•
boundary, min_scale, and max_scale are enforced by the shared runtime, independent of renderer.
•
clip controls whether transformed content is clipped at the viewport edge.
Interactive descendants win a single-pointer drag. Multi-touch remains reserved for the nearest viewer so pinch gestures are reliable around draggable children.
Related
InfiniteCanvas, Transform, GestureDetector, and Clip.
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