无法检索合成动画缺少的变量

Question

我正在尝试使用Composition Api和Expression Builder应用指针动画。我已经找到了一个我需要的样本，但代码不完整，我不知道如何获得变量center和distanceToCenter的值。原始文档和样本在这里：

https://learn.microsoft.com/en-us/windows/uwp/composition/pointer-input-animations

示例代码(略有修改(：

using Microsoft.Toolkit.Uwp.UI.Animations.Expressions;
using EF = Microsoft.Toolkit.Uwp.UI.Animations.Expressions.ExpressionFunctions;
_tiltVisual = ElementCompositionPreview.GetElementVisual(element);
_pointerPositionPropSet = ElementCompositionPreview.GetPointerPositionPropertySet(element);
// || DEFINE THE EXPRESSION FOR THE ROTATION ANGLE ||
var hoverPosition = _pointerPositionPropSet.GetSpecializedReference<PointerPositionPropertySetReferenceNode>().Position;
var angleExpressionNode = EF.Conditional(hoverPosition == new Vector3(0, 0, 0),
ExpressionValues.CurrentValue.CreateScalarCurrentValue(),
35 * ((EF.Clamp(EF.Distance(center, hoverPosition), 0, distanceToCenter) % distanceToCenter) / distanceToCenter));
_tiltVisual.StartAnimation("RotationAngleInDegrees", angleExpressionNode);
// || DEFINE THE EXPRESSION FOR THE ROTATION AXIS ||
var axisAngleExpressionNode = EF.Vector3(-(hoverPosition.Y - center.Y) * EF.Conditional(hoverPosition.Y == center.Y, 0, 1),
(hoverPosition.X - center.X) * EF.Conditional(hoverPosition.X == center.X, 0, 1),
0);
_tiltVisual.StartAnimation("RotationAxis", axisAngleExpressionNode);

Answer 1

感谢Xavier Xie，我找到了完整的代码：

// Grab the backing Visual for the UIElement image
_tiltVisual = ElementCompositionPreview.GetElementVisual(tiltImage);
// Set the CenterPoint of the backing Visual, so the rotation axis will defined from the middle
_tiltVisual.CenterPoint = new Vector3((float)tiltImage.Width / 2, (float)tiltImage.Height / 2, 0f);
// Grab the PropertySet containing the hover pointer data that will be used to drive the rotations
// Note: We have a second UIElement we will grab the pointer data against and the other we will animate
_hoverPositionPropertySet = ElementCompositionPreview.GetPointerPositionPropertySet(HitTestRect);
// Calculate distance from corner of quadrant to Center
var center = new Vector3((float)tiltImage.Width / 2, (float)tiltImage.Height / 2, 0);
var xSquared = Math.Pow(tiltImage.Width / 2, 2);
var ySquared = Math.Pow(tiltImage.Height / 2, 2);
var distanceToCenter = (float)Math.Sqrt(xSquared + ySquared);
// || DEFINE THE EXPRESSION FOR THE ROTATION ANGLE ||             
// We calculate the Rotation Angle such that it increases from 0 to 35 as the cursor position moves away from the center.
// Combined with animating the Rotation Axis, the image is "push down" on the point at which the cursor is located.
// Note: We special case when the hover position is (0,0,0) as this is the starting hover position and and we want the image to be flat (rotationAngle = 0) at startup.             
var hoverPosition = _hoverPositionPropertySet.GetSpecializedReference<PointerPositionPropertySetReferenceNode>().Position;
var angleExpressionNode =
EF.Conditional(
hoverPosition == new Vector3(0, 0, 0),
ExpressionValues.CurrentValue.CreateScalarCurrentValue(),
35 * ((EF.Clamp(EF.Distance(center, hoverPosition), 0, distanceToCenter) % distanceToCenter) / distanceToCenter));
_tiltVisual.StartAnimation("RotationAngleInDegrees", angleExpressionNode);
// || DEFINE THE EXPRESSION FOR THE ROTATION AXIS ||             
// The RotationAxis will be defined as the axis perpendicular to vector position of the hover pointer (vector from center to hover position).
// The axis is a vector calculated by first converting the pointer position into the coordinate space where the center point (0, 0) is in the middle.
// The perpendicular axis is then calculated by transposing the cartesian x, y components and negating one (e.g. Vector3(-y,x,0) )
var axisAngleExpressionNode = EF.Vector3(
-(hoverPosition.Y - center.Y) * EF.Conditional(hoverPosition.Y == center.Y, 0, 1),
(hoverPosition.X - center.X) * EF.Conditional(hoverPosition.X == center.X, 0, 1),
0);
_tiltVisual.StartAnimation("RotationAxis", axisAngleExpressionNode);