RenderListWheelViewport class

Render, onto a wheel, a bigger sequential set of objects inside this viewport.

Takes a scrollable set of fixed sized RenderBoxes and renders them sequentially from top down on a vertical scrolling axis.

It starts with the first scrollable item in the center of the main axis and ends with the last scrollable item in the center of the main axis. This is in contrast to typical lists that start with the first scrollable item at the start of the main axis and ends with the last scrollable item at the end of the main axis.

Instead of rendering its children on a flat plane, it renders them as if each child is broken into its own plane and that plane is perpendicularly fixed onto a cylinder which rotates along the scrolling axis.

This class works in 3 coordinate systems:

  1. The scrollable layout coordinates. This coordinate system is used to communicate with ViewportOffset and describes its children's abstract offset from the beginning of the scrollable list at (0.0, 0.0).

    The list is scrollable from the start of the first child item to the start of the last child item.

    Children's layout coordinates don't change as the viewport scrolls.

  2. The untransformed plane's viewport painting coordinates. Children are not painted in this coordinate system. It's an abstract intermediary used before transforming into the next cylindrical coordinate system.

    This system is the scrollable layout coordinates translated by the scroll offset such that (0.0, 0.0) is the top left corner of the viewport.

    Because the viewport is centered at the scrollable list's scroll offset instead of starting at the scroll offset, there are paintable children ~1/2 viewport length before and after the scroll offset instead of ~1 viewport length after the scroll offset.

    Children's visibility inclusion in the viewport is determined in this system regardless of the cylinder's properties such as diameterRatio or perspective. In other words, a 100px long viewport will always paint 10-11 visible 10px children if there are enough children in the viewport.

  3. The transformed cylindrical space viewport painting coordinates. Children from system 2 get their positions transformed into a cylindrical projection matrix instead of its Cartesian offset with respect to the scroll offset.

    Children in this coordinate system are painted.

    The wheel's size and the maximum and minimum visible angles are both controlled by diameterRatio. Children visible in the untransformed plane's viewport painting coordinates's viewport will be radially evenly laid out between the maximum and minimum angles determined by intersecting the viewport's main axis length with a cylinder whose diameter is diameterRatio times longer, as long as those angles are between -pi/2 and pi/2.

    For example, if diameterRatio is 2.0 and this RenderListWheelViewport is 100.0px in the main axis, then the diameter is 200.0. And children will be evenly laid out between that cylinder's -arcsin(1/2) and arcsin(1/2) angles.

    The cylinder's 0 degree side is always centered in the RenderListWheelViewport. The transformation from untransformed plane's viewport painting coordinates is also done such that the child in the center of that plane will be mostly untransformed with children above and below it being transformed more as the angle increases.

Inheritance
Implemented types
Mixed in types

Constructors

RenderListWheelViewport({required ListWheelChildManager childManager, required ViewportOffset offset, double diameterRatio = defaultDiameterRatio, double perspective = defaultPerspective, double offAxisFraction = 0, bool useMagnifier = false, double magnification = 1, double overAndUnderCenterOpacity = 1, required double itemExtent, double squeeze = 1, bool renderChildrenOutsideViewport = false, Clip clipBehavior = Clip.none, List<RenderBox>? children})
Creates a RenderListWheelViewport which renders children on a wheel.

Properties

alwaysNeedsCompositing bool
Whether this render object always needs compositing.
no setterinherited
attached bool
Whether the render tree this render object belongs to is attached to a PipelineOwner.
no setterinherited
childCount int
The number of children.
no setterinherited
childManager ListWheelChildManager
The delegate that manages the children of this object.
final
clipBehavior Clip
The content will be clipped (or not) according to this option.
getter/setter pair
constraints BoxConstraints
The box constraints most recently received from the parent.
no setterinherited
debugCanParentUseSize bool
Whether the parent render object is permitted to use this render object's size.
no setterinherited
debugCreator Object?
The object responsible for creating this render object.
getter/setter pairinherited
debugDisposed bool?
Whether this has been disposed.
no setterinherited
debugDoingThisLayout bool
Whether performLayout for this render object is currently running.
no setterinherited
debugDoingThisLayoutWithCallback bool
Whether invokeLayoutCallback for this render object is currently running.
no setterinherited
debugDoingThisPaint bool
Whether paint for this render object is currently running.
no setterinherited
debugDoingThisResize bool
Whether performResize for this render object is currently running.
no setterinherited
debugLayer ContainerLayer?
In debug mode, the compositing layer that this render object uses to repaint.
no setterinherited
debugLayoutParent RenderObject?
The RenderObject that's expected to call layout on this RenderObject in its performLayout implementation.
no setterinherited
debugNeedsCompositedLayerUpdate bool
Whether this render object's layer information is dirty.
no setterinherited
debugNeedsLayout bool
Whether this render object's layout information is dirty.
no setterinherited
debugNeedsPaint bool
Whether this render object's paint information is dirty.
no setterinherited
debugSemantics SemanticsNode?
The semantics of this render object.
no setterinherited
depth int
The depth of this render object in the render tree.
no setterinherited
diameterRatio double
A ratio between the diameter of the cylinder and the viewport's size in the main axis.
getter/setter pair
firstChild RenderBox?
The first child in the child list.
no setterinherited
hashCode int
The hash code for this object.
no setterinherited
hasSize bool
Whether this render object has undergone layout and has a size.
no setterinherited
isRepaintBoundary bool
Whether this render object repaints separately from its parent.
no setteroverride
itemExtent double
The size of the children along the main axis. Children RenderBoxes will be given the BoxConstraints of this exact size.
getter/setter pair
lastChild RenderBox?
The last child in the child list.
no setterinherited
layer ContainerLayer?
The compositing layer that this render object uses to repaint.
getter/setter pairinherited
magnification double
The zoomed-in rate of the magnifier, if it is used.
getter/setter pair
needsCompositing bool
Whether we or one of our descendants has a compositing layer.
no setterinherited
offAxisFraction double
How much the wheel is horizontally off-center, as a fraction of its width. This property creates the visual effect of looking at a vertical wheel from its side where its vanishing points at the edge curves to one side instead of looking at the wheel head-on.
getter/setter pair
offset ViewportOffset
The associated ViewportOffset object for the viewport describing the part of the content inside that's visible.
getter/setter pair
overAndUnderCenterOpacity double
The opacity value that will be applied to the wheel that appears below and above the magnifier.
getter/setter pair
owner PipelineOwner?
The owner for this render object (null if unattached).
no setterinherited
paintBounds Rect
Returns a rectangle that contains all the pixels painted by this box.
no setterinherited
parent RenderObject?
The parent of this render object in the render tree.
no setterinherited
parentData ParentData?
Data for use by the parent render object.
getter/setter pairinherited
perspective double
Perspective of the cylindrical projection.
getter/setter pair
renderChildrenOutsideViewport bool
Whether to paint children inside the viewport only.
getter/setter pair
runtimeType Type
A representation of the runtime type of the object.
no setterinherited
semanticBounds Rect
The bounding box, in the local coordinate system, of this object, for accessibility purposes.
no setterinherited
size Size
The size of this render box computed during layout.
getter/setter pairinherited
sizedByParent bool
Whether the constraints are the only input to the sizing algorithm (in particular, child nodes have no impact).
no setteroverride
squeeze double
The angular compactness of the children on the wheel.
getter/setter pair
useMagnifier bool
Whether to use the magnifier for the center item of the wheel.
getter/setter pair

Methods

add(RenderBox child) → void
Append child to the end of this render object's child list.
inherited
addAll(List<RenderBox>? children) → void
Add all the children to the end of this render object's child list.
inherited
adoptChild(RenderObject child) → void
Called by subclasses when they decide a render object is a child.
inherited
applyPaintTransform(covariant RenderBox child, Matrix4 transform) → void
Multiply the transform from the parent's coordinate system to this box's coordinate system into the given transform.
override
assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) → void
Assemble the SemanticsNode for this RenderObject.
inherited
attach(PipelineOwner owner) → void
Mark this render object as attached to the given owner.
override
childAfter(RenderBox child) RenderBox?
The next child after the given child in the child list.
inherited
childBefore(RenderBox child) RenderBox?
The previous child before the given child in the child list.
inherited
clearSemantics() → void
Removes all semantics from this render object and its descendants.
inherited
computeDistanceToActualBaseline(TextBaseline baseline) double?
Returns the distance from the y-coordinate of the position of the box to the y-coordinate of the first given baseline in the box's contents, if any, or null otherwise.
inherited
computeDryLayout(covariant BoxConstraints constraints) Size
Computes the value returned by getDryLayout. Do not call this function directly, instead, call getDryLayout.
override
computeMaxIntrinsicHeight(double width) double
Computes the value returned by getMaxIntrinsicHeight. Do not call this function directly, instead, call getMaxIntrinsicHeight.
override
computeMaxIntrinsicWidth(double height) double
Computes the value returned by getMaxIntrinsicWidth. Do not call this function directly, instead, call getMaxIntrinsicWidth.
override
computeMinIntrinsicHeight(double width) double
Computes the value returned by getMinIntrinsicHeight. Do not call this function directly, instead, call getMinIntrinsicHeight.
override
computeMinIntrinsicWidth(double height) double
Computes the value returned by getMinIntrinsicWidth. Do not call this function directly, instead, call getMinIntrinsicWidth.
override
debugAdoptSize(Size value) Size
Claims ownership of the given Size.
inherited
debugAssertDoesMeetConstraints() → void
Verify that the object's constraints are being met. Override this function in a subclass to verify that your state matches the constraints object. This function is only called in checked mode and only when needsLayout is false. If the constraints are not met, it should assert or throw an exception.
inherited
debugCannotComputeDryLayout({String? reason, FlutterError? error}) bool
Called from computeDryLayout within an assert if the given RenderBox subclass does not support calculating a dry layout.
inherited
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
debugHandleEvent(PointerEvent event, HitTestEntry<HitTestTarget> entry) bool
Implements the debugPaintPointersEnabled debugging feature.
inherited
debugPaint(PaintingContext context, Offset offset) → void
Override this method to paint debugging information.
inherited
debugPaintBaselines(PaintingContext context, Offset offset) → void
In debug mode, paints a line for each baseline.
inherited
debugPaintPointers(PaintingContext context, Offset offset) → void
In debug mode, paints a rectangle if this render box has counted more pointer downs than pointer up events.
inherited
debugPaintSize(PaintingContext context, Offset offset) → void
In debug mode, paints a border around this render box.
inherited
debugRegisterRepaintBoundaryPaint({bool includedParent = true, bool includedChild = false}) → void
Called, in debug mode, if isRepaintBoundary is true, when either the this render object or its parent attempt to paint.
inherited
debugResetSize() → void
If a subclass has a "size" (the state controlled by parentUsesSize, whatever it is in the subclass, e.g. the actual size property of RenderBox), and the subclass verifies that in debug mode this "size" property isn't used when debugCanParentUseSize isn't set, then that subclass should override debugResetSize to reapply the current values of debugCanParentUseSize to that state.
inherited
debugValidateChild(RenderObject child) bool
Checks whether the given render object has the correct runtimeType to be a child of this render object.
inherited
describeApproximatePaintClip(covariant RenderObject child) Rect?
Returns a rect in this object's coordinate system that describes the approximate bounding box of the clip rect that would be applied to the given child during the paint phase, if any.
override
describeForError(String name, {DiagnosticsTreeStyle style = DiagnosticsTreeStyle.shallow}) DiagnosticsNode
Adds a debug representation of a RenderObject optimized for including in error messages.
inherited
describeSemanticsClip(covariant RenderObject? child) Rect?
Returns a rect in this object's coordinate system that describes which SemanticsNodes produced by the child should be included in the semantics tree. SemanticsNodes from the child that are positioned outside of this rect will be dropped. Child SemanticsNodes that are positioned inside this rect, but outside of describeApproximatePaintClip will be included in the tree marked as hidden. Child SemanticsNodes that are inside of both rect will be included in the tree as regular nodes.
inherited
describeSemanticsConfiguration(SemanticsConfiguration config) → void
Report the semantics of this node, for example for accessibility purposes.
inherited
detach() → void
Mark this render object as detached from its PipelineOwner.
override
dispose() → void
Release any resources held by this render object.
override
dropChild(RenderObject child) → void
Called by subclasses when they decide a render object is no longer a child.
inherited
getDistanceToActualBaseline(TextBaseline baseline) double?
Calls computeDistanceToActualBaseline and caches the result.
inherited
getDistanceToBaseline(TextBaseline baseline, {bool onlyReal = false}) double?
Returns the distance from the y-coordinate of the position of the box to the y-coordinate of the first given baseline in the box's contents.
inherited
getDryLayout(BoxConstraints constraints) Size
Returns the Size that this RenderBox would like to be given the provided BoxConstraints.
inherited
getMaxIntrinsicHeight(double width) double
Returns the smallest height beyond which increasing the height never decreases the preferred width. The preferred width is the value that would be returned by getMinIntrinsicWidth for that height.
inherited
getMaxIntrinsicWidth(double height) double
Returns the smallest width beyond which increasing the width never decreases the preferred height. The preferred height is the value that would be returned by getMinIntrinsicHeight for that width.
inherited
getMinIntrinsicHeight(double width) double
Returns the minimum height that this box could be without failing to correctly paint its contents within itself, without clipping.
inherited
getMinIntrinsicWidth(double height) double
Returns the minimum width that this box could be without failing to correctly paint its contents within itself, without clipping.
inherited
getOffsetToReveal(RenderObject target, double alignment, {Rect? rect, Axis? axis}) RevealedOffset
Returns the offset that would be needed to reveal the target RenderObject.
override
getTransformTo(RenderObject? ancestor) Matrix4
Applies the paint transform up the tree to ancestor.
inherited
globalToLocal(Offset point, {RenderObject? ancestor}) Offset
Convert the given point from the global coordinate system in logical pixels to the local coordinate system for this box.
inherited
handleEvent(PointerEvent event, covariant BoxHitTestEntry entry) → void
Override this method to handle pointer events that hit this render object.
inherited
hitTest(BoxHitTestResult result, {required Offset position}) bool
Determines the set of render objects located at the given position.
inherited
hitTestChildren(BoxHitTestResult result, {required Offset position}) bool
Override this method to check whether any children are located at the given position.
override
hitTestSelf(Offset position) bool
Override this method if this render object can be hit even if its children were not hit.
inherited
indexOf(RenderBox child) int
Gets the index of a child by looking at its parentData.
indexToScrollOffset(int index) double
Returns the scroll offset of the child with the given index.
insert(RenderBox child, {RenderBox? after}) → void
Insert child into this render object's child list after the given child.
inherited
invokeLayoutCallback<T extends Constraints>(LayoutCallback<T> callback) → void
Allows mutations to be made to this object's child list (and any descendants) as well as to any other dirty nodes in the render tree owned by the same PipelineOwner as this object. The callback argument is invoked synchronously, and the mutations are allowed only during that callback's execution.
inherited
layout(Constraints constraints, {bool parentUsesSize = false}) → void
Compute the layout for this render object.
inherited
localToGlobal(Offset point, {RenderObject? ancestor}) Offset
Convert the given point from the local coordinate system for this box to the global coordinate system in logical pixels.
inherited
markNeedsCompositedLayerUpdate() → void
Mark this render object as having changed a property on its composited layer.
inherited
markNeedsCompositingBitsUpdate() → void
Mark the compositing state for this render object as dirty.
inherited
markNeedsLayout() → void
Mark this render object's layout information as dirty, and either register this object with its PipelineOwner, or defer to the parent, depending on whether this object is a relayout boundary or not respectively.
inherited
markNeedsLayoutForSizedByParentChange() → void
Mark this render object's layout information as dirty (like markNeedsLayout), and additionally also handle any necessary work to handle the case where sizedByParent has changed value.
inherited
markNeedsPaint() → void
Mark this render object as having changed its visual appearance.
inherited
markNeedsSemanticsUpdate() → void
Mark this node as needing an update to its semantics description.
inherited
markParentNeedsLayout() → void
Mark this render object's layout information as dirty, and then defer to the parent.
inherited
move(RenderBox child, {RenderBox? after}) → void
Move the given child in the child list to be after another child.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
paint(PaintingContext context, Offset offset) → void
Paint this render object into the given context at the given offset.
override
paintsChild(covariant RenderObject child) bool
Whether the given child would be painted if paint were called.
inherited
performLayout() → void
Performs layout based on how childManager provides children.
override
performResize() → void
Updates the render objects size using only the constraints.
inherited
reassemble() → void
Cause the entire subtree rooted at the given RenderObject to be marked dirty for layout, paint, etc, so that the effects of a hot reload can be seen, or so that the effect of changing a global debug flag (such as debugPaintSizeEnabled) can be applied.
inherited
redepthChild(RenderObject child) → void
Adjust the depth of the given child to be greater than this node's own depth.
inherited
redepthChildren() → void
Adjust the depth of this node's children, if any.
inherited
remove(RenderBox child) → void
Remove this child from the child list.
inherited
removeAll() → void
Remove all their children from this render object's child list.
inherited
replaceRootLayer(OffsetLayer rootLayer) → void
Replace the layer. This is only valid for the root of a render object subtree (whatever object scheduleInitialPaint was called on).
inherited
scheduleInitialLayout() → void
Bootstrap the rendering pipeline by scheduling the very first layout.
inherited
scheduleInitialPaint(ContainerLayer rootLayer) → void
Bootstrap the rendering pipeline by scheduling the very first paint.
inherited
scheduleInitialSemantics() → void
Bootstrap the semantics reporting mechanism by marking this node as needing a semantics update.
inherited
scrollOffsetToIndex(double scrollOffset) int
Returns the index of the child at the given offset.
sendSemanticsEvent(SemanticsEvent semanticsEvent) → void
Sends a SemanticsEvent associated with this render object's SemanticsNode.
inherited
setupParentData(covariant RenderObject child) → void
Override to setup parent data correctly for your children.
override
showOnScreen({RenderObject? descendant, Rect? rect, Duration duration = Duration.zero, Curve curve = Curves.ease}) → void
Attempt to make (a portion of) this or a descendant RenderObject visible on screen.
override
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) String
A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines = '', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a description of the tree rooted at this node. If the prefix argument is provided, then every line in the output will be prefixed by that string.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a one-line detailed description of the render object. This description is often somewhat long.
inherited
toStringShort() String
Returns a human understandable name.
inherited
updateCompositedLayer({required covariant OffsetLayer? oldLayer}) OffsetLayer
Update the composited layer owned by this render object.
inherited
visitChildren(RenderObjectVisitor visitor) → void
Calls visitor for each immediate child of this render object.
inherited
visitChildrenForSemantics(RenderObjectVisitor visitor) → void
Called when collecting the semantics of this node.
inherited

Operators

operator ==(Object other) bool
The equality operator.
inherited

Constants

clipBehaviorAndRenderChildrenOutsideViewportConflict → const String
An error message to show when clipBehavior and renderChildrenOutsideViewport are set to conflicting values.
defaultDiameterRatio → const double
An arbitrary but aesthetically reasonable default value for diameterRatio.
defaultPerspective → const double
An arbitrary but aesthetically reasonable default value for perspective.
diameterRatioZeroMessage → const String
An error message to show when the provided diameterRatio is zero.
perspectiveTooHighMessage → const String
An error message to show when the perspective value is too high.