showInViewport static method
- RenderObject? descendant,
- Rect? rect,
- required RenderAbstractViewport viewport,
- required ViewportOffset offset,
- Duration duration = Duration.zero,
- Curve curve = Curves.ease,
Make (a portion of) the given descendant
of the given viewport
fully
visible in the viewport
by manipulating the provided ViewportOffset
offset
.
The optional rect
parameter describes which area of the descendant
should be shown in the viewport. If rect
is null, the entire
descendant
will be revealed. The rect
parameter is interpreted
relative to the coordinate system of descendant
.
The returned Rect describes the new location of descendant
or rect
in the viewport after it has been revealed. See RevealedOffset.rect
for a full definition of this Rect.
If descendant
is null, this is a no-op and rect
is returned.
If both descendant
and rect
are null, null is returned because there is
nothing to be shown in the viewport.
The duration
parameter can be set to a non-zero value to animate the
target object into the viewport with an animation defined by curve
.
See also:
- RenderObject.showOnScreen, overridden by RenderViewportBase and the renderer for SingleChildScrollView to delegate to this method.
Implementation
static Rect? showInViewport({
RenderObject? descendant,
Rect? rect,
required RenderAbstractViewport viewport,
required ViewportOffset offset,
Duration duration = Duration.zero,
Curve curve = Curves.ease,
}) {
if (descendant == null) {
return rect;
}
final RevealedOffset leadingEdgeOffset = viewport.getOffsetToReveal(descendant, 0.0, rect: rect);
final RevealedOffset trailingEdgeOffset = viewport.getOffsetToReveal(descendant, 1.0, rect: rect);
final double currentOffset = offset.pixels;
final RevealedOffset? targetOffset = RevealedOffset.clampOffset(
leadingEdgeOffset: leadingEdgeOffset,
trailingEdgeOffset: trailingEdgeOffset,
currentOffset: currentOffset,
);
if (targetOffset == null) {
// `descendant` is between leading and trailing edge and hence already
// fully shown on screen. No action necessary.
assert(viewport.parent != null);
final Matrix4 transform = descendant.getTransformTo(viewport.parent);
return MatrixUtils.transformRect(transform, rect ?? descendant.paintBounds);
}
offset.moveTo(targetOffset.offset, duration: duration, curve: curve);
return targetOffset.rect;
}