WPFCanvas画区域

2019-11-14 15:51:55

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有时候需要实现类似于QQ截图那样的选择区域功能，这里的区域可以是一条线，圆，矩形等等

实现原理就是一个Canvas做蒙板，然后canvas的三个事件，MouseLeftButtonDown，MouseMove，MouseLeftButtonUp。非常easy！

首先，你要有个canvas

<Canvas Name="videocanvas" Height="288" Width="352" Background="Transparent" MouseMove="image_MouseMove" MouseLeftButtonDown="Mask_MouseLeftButtonDown" MouseLeftButtonUp="Mask_MouseLeftButtonUp"/>

然后实现他的事件，在之前我们先决定一下到底是什么形状的区域。

1 public static Shape CreateShape()2 {3     //矩形区域4     return new System.Windows.Shapes.Rectangle() { Fill = null, Stroke = System.Windows.Media.Brushes.Red, StrokeThickness = 1 };5     //圆形区域6     //return new System.Windows.Shapes.Ellipse() { Fill = null, Stroke = System.Windows.Media.Brushes.Red, StrokeThickness = 1 };7 8 }

然后实现三个事件

bool drawFlag = false;Shape insertShape;System.Windows.Point startPosition;PRivate void Mask_MouseLeftButtonDown(object sender, MouseButtonEventArgs e){    insertShape = CreateShape();    if (insertShape != null)    {        drawFlag = true;        Canvas board = sender as Canvas;        board.Children.Clear();        startPosition = e.GetPosition(board);        insertShape.Opacity = 1;        Canvas.SetLeft(insertShape, e.GetPosition(board).X);        Canvas.SetTop(insertShape, e.GetPosition(board).Y);        board.Children.Add(insertShape);    }}private void image_MouseMove(object sender, MouseEventArgs e){    Canvas board = sender as Canvas;    if (drawFlag && insertShape != null)    {        if (e.GetPosition(board).X > startPosition.X)        {            insertShape.Width = e.GetPosition(board).X - startPosition.X;                    }        else        {            insertShape.Width = startPosition.X - e.GetPosition(board).X;            Canvas.SetLeft(insertShape, e.GetPosition(board).X);        }        if (e.GetPosition(board).Y > startPosition.Y)        {            insertShape.Height = e.GetPosition(board).Y - startPosition.Y;        }        else        {            insertShape.Height = startPosition.Y - e.GetPosition(board).Y;            Canvas.SetTop(insertShape, e.GetPosition(board).Y);        }    }}private void Mask_MouseLeftButtonUp(object sender, MouseButtonEventArgs e){    drawFlag = false;    if (insertShape != null)    {        insertShape.Opacity = 1;        System.Windows.Point p = e.GetPosition(sender as Canvas);        Canvas.SetLeft(insertShape, e.GetPosition(board).X);        Canvas.SetTop(insertShape, e.GetPosition(board).Y);    }}