二维图形的矩阵变换（三）——在WPF中的应用矩阵变换

原文:二维图形的矩阵变换（三）——在WPF中的应用矩阵变换UIElement和RenderTransform

首先，我们来看看什么样的对象可以进行变换。在WPF中，用于呈现给用户的对象的基类为Visual类，但是Visual对象并不具有变换功能，具有变换功能的是它的子类UIElement。这个类也是非常底层的类了，几乎我们所有的常用控件都是继承自它，也就是说，基本上所有的UI对象都是可以应用变换的。

然后，我们在再来看看UIElement中变换种类。UIElement支持两种变换：RenderTransform和LayoutTransform，其中LayoutTransform是会改变其布局，从而影响相邻的空间大小和位置的，如下图所示。

public class MatrixAnimation : MatrixAnimationBase
{
public Matrix? From
{
set { SetValue(FromProperty, value); }
get { return (Matrix?)GetValue(FromProperty); }
}

public static DependencyProperty FromProperty =
DependencyProperty.Register("From", typeof(Matrix?), typeof(MatrixAnimation),
new PropertyMetadata(null));

public Matrix? To
{
set { SetValue(ToProperty, value); }
get { return (Matrix?)GetValue(ToProperty); }
}

public static DependencyProperty ToProperty =
DependencyProperty.Register("To", typeof(Matrix?), typeof(MatrixAnimation),
new PropertyMetadata(null));

public IEasingFunction EasingFunction
{
get { return (IEasingFunction)GetValue(EasingFunctionProperty); }
set { SetValue(EasingFunctionProperty, value); }
}

public static readonly DependencyProperty EasingFunctionProperty =
DependencyProperty.Register("EasingFunction", typeof(IEasingFunction), typeof(MatrixAnimation),
new UIPropertyMetadata(null));

public MatrixAnimation()
{
}

public MatrixAnimation(Matrix toValue, Duration duration)
{
To = toValue;
Duration = duration;
}

public MatrixAnimation(Matrix toValue, Duration duration, FillBehavior fillBehavior)
{
To = toValue;
Duration = duration;
FillBehavior = fillBehavior;
}

public MatrixAnimation(Matrix fromValue, Matrix toValue, Duration duration)
{
From = fromValue;
To = toValue;
Duration = duration;
}

public MatrixAnimation(Matrix fromValue, Matrix toValue, Duration duration, FillBehavior fillBehavior)
{
From = fromValue;
To = toValue;
Duration = duration;
FillBehavior = fillBehavior;
}

protected override Freezable CreateInstanceCore()
{
return new MatrixAnimation();
}

protected override Matrix GetCurrentValueCore(Matrix defaultOriginValue, Matrix defaultDestinationValue, AnimationClock animationClock)
{
if (animationClock.CurrentProgress == null)
{
return Matrix.Identity;
}

var normalizedTime = animationClock.CurrentProgress.Value;
if (EasingFunction != null)
{
normalizedTime = EasingFunction.Ease(normalizedTime);
}

var from = From ?? defaultOriginValue;
var to = To ?? defaultDestinationValue;

var newMatrix = new Matrix(
((to.M11 - from.M11) * normalizedTime) + from.M11,
((to.M12 - from.M12) * normalizedTime) + from.M12,
((to.M21 - from.M21) * normalizedTime) + from.M21,
((to.M22 - from.M22) * normalizedTime) + from.M22,
((to.OffsetX - from.OffsetX) * normalizedTime) + from.OffsetX,
((to.OffsetY - from.OffsetY) * normalizedTime) + from.OffsetY);

return newMatrix;
}
}

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