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分享在WPF中如何使用scrollviewer放大图片并通过鼠标画出选区，保存这个选区到一张图片？
需求是这样的，我在做一个图片查看器
其中，使用了scrollviewer来放大或者缩小图片
这一步我已经实现了
然后在图片上，绘制矩形选取，这一步我也实现了
但是接下来遇到两个问题：
1、因为我的矩形选区是放在scrollviewer里的，导致随着图片放大缩小，矩形的边框会变粗或者变细。（不是我想把矩形选区是放在scrollviewer里，而是不放在里面就无法在图片上画选区）
2、我无法截取矩形选取内的图片，截取后是空白的，
以下是代码，请问该如何解决，谢谢！
xaml：
后台代码：
其中，使用了scrollviewer来放大或者缩小图片
这一步我已经实现了
然后在图片上，绘制矩形选取，这一步我也实现了
但是接下来遇到两个问题：
1、因为我的矩形选区是放在scrollviewer里的，导致随着图片放大缩小，矩形的边框会变粗或者变细。（不是我想把矩形选区是放在scrollviewer里，而是不放在里面就无法在图片上画选区）
2、我无法截取矩形选取内的图片，截取后是空白的，
以下是代码，请问该如何解决，谢谢！
xaml：
<Window x:Class="截图.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:截图"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Slider Grid.Column="0" Orientation="Vertical" HorizontalAlignment="Left" Minimum="1" x:Name="slider"/>
<ScrollViewer Name="scrollViewer" Grid.Column="1"
VerticalScrollBarVisibility="Visible"
HorizontalScrollBarVisibility="Visible" Margin="0,0,0,40">
<Grid Name="grid" Width="400" Height="400" >
<Grid.LayoutTransform>
<TransformGroup x:Name="TfGroup">
<ScaleTransform x:Name="scaleTransform"/>
</TransformGroup>
</Grid.LayoutTransform>
<Image x:Name="img" Source="C:\Users\howze\Desktop\20200728104010.png" />
<Canvas x:Name="canvas" MouseDown="Canvas_MouseDown" MouseMove="Canvas_MouseMove" MouseUp="Canvas_MouseUp" Background="Transparent"/>
</Grid>
</ScrollViewer>
<Button Grid.Column="1" Content="Capture" Margin="338,381,337.333,9.667" Click="Button_Click"/>
</Grid>
</Window>
后台代码：
public partial class MainWindow : Window
{
Point? lastCenterPositionOnTarget;
Point? lastMousePositionOnTarget;
Point? lastDragPoint;
private System.Windows.Point startPoint;
private System.Windows.Shapes.Rectangle rect;
private int w1;
private int h1;
public MainWindow()
{
InitializeComponent();
scrollViewer.ScrollChanged += OnScrollViewerScrollChanged;
scrollViewer.PreviewMouseWheel += OnPreviewMouseWheel;
slider.ValueChanged += OnSliderValueChanged;
}
void OnScrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
{
if (e.ExtentHeightChange != 0 || e.ExtentWidthChange != 0)
{
Point? targetBefore = null;
Point? targetNow = null;
if (!lastMousePositionOnTarget.HasValue)
{
if (lastCenterPositionOnTarget.HasValue)
{
var centerOfViewport = new Point(scrollViewer.ViewportWidth / 2,
scrollViewer.ViewportHeight / 2);
Point centerOfTargetNow =
scrollViewer.TranslatePoint(centerOfViewport, grid);
targetBefore = lastCenterPositionOnTarget;
targetNow = centerOfTargetNow;
}
}
else
{
targetBefore = lastMousePositionOnTarget;
targetNow = Mouse.GetPosition(grid);
lastMousePositionOnTarget = null;
}
if (targetBefore.HasValue)
{
double dXInTargetPixels = targetNow.Value.X - targetBefore.Value.X;
double dYInTargetPixels = targetNow.Value.Y - targetBefore.Value.Y;
double multiplicatorX = e.ExtentWidth / grid.Width;
double multiplicatorY = e.ExtentHeight / grid.Height;
double newOffsetX = scrollViewer.HorizontalOffset -
dXInTargetPixels * multiplicatorX;
double newOffsetY = scrollViewer.VerticalOffset -
dYInTargetPixels * multiplicatorY;
if (double.IsNaN(newOffsetX) || double.IsNaN(newOffsetY))
{
return;
}
scrollViewer.ScrollToHorizontalOffset(newOffsetX);
scrollViewer.ScrollToVerticalOffset(newOffsetY);
}
}
}
private void OnPreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
lastMousePositionOnTarget = Mouse.GetPosition(grid);
System.Windows.Point centerPoint = e.GetPosition(img);
var val = e.Delta * 0.01; //描述鼠标滑轮滚动
if (scaleTransform.ScaleX + val < 0.1) return;
if (scaleTransform.ScaleX + val > 100) return;
scaleTransform.CenterX = centerPoint.X;
scaleTransform.CenterY = centerPoint.Y;
scaleTransform.ScaleX += val;
scaleTransform.ScaleY += val;
if (e.Delta > 0)
{
slider.Value += 1;
}
if (e.Delta < 0)
{
slider.Value -= 1;
}
e.Handled = true;
}
private void OnSliderValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
scaleTransform.ScaleX = e.NewValue;
scaleTransform.ScaleY = e.NewValue;
var centerOfViewport = new System.Windows.Point(scrollViewer.ViewportWidth / 2, scrollViewer.ViewportHeight / 2);
lastCenterPositionOnTarget = scrollViewer.TranslatePoint(centerOfViewport, grid);
}
private void Canvas_MouseDown(object sender, MouseButtonEventArgs e)
{
canvas.Children.Clear();
startPoint = e.GetPosition(canvas);
//MessageBox.Show(startPoint.ToString());
rect = new System.Windows.Shapes.Rectangle
{
Stroke = System.Windows.Media.Brushes.IndianRed,
StrokeThickness = 0.2,
StrokeDashArray = new DoubleCollection { 2 }
};
Canvas.SetLeft(rect, startPoint.X);
Canvas.SetTop(rect, startPoint.Y);
canvas.Children.Add(rect);
}
private void Canvas_MouseMove(object sender, MouseEventArgs e)
{
if (e.LeftButton == MouseButtonState.Released || rect == null)
return;
var pos = e.GetPosition(canvas);
var x = Math.Min(pos.X, startPoint.X);
var y = Math.Min(pos.Y, startPoint.Y);
var w = Math.Max(pos.X, startPoint.X) - x;
var h = Math.Max(pos.Y, startPoint.Y) - y;
w1 = (int)w;
h1 = (int)h;
rect.Width = w;
rect.Height = h;
Canvas.SetLeft(rect, x);
Canvas.SetTop(rect, y);
}
private void Canvas_MouseUp(object sender, MouseButtonEventArgs e)
{
}
private void Button_Click(object sender, RoutedEventArgs e)
{
RenderTargetBitmap targetBitmap = new RenderTargetBitmap(
(int)canvas.ActualWidth,
(int)canvas.ActualHeight,
96,
96,
PixelFormats.Default);
targetBitmap.Render(canvas);
using (FileStream tFileStream = new FileStream(@"C:\Users\howze\Desktop\test.jpg",
FileMode.Create, FileAccess.Write))
{
PngBitmapEncoder tPngBitmapEncoder = new PngBitmapEncoder();
tPngBitmapEncoder.Interlace = PngInterlaceOption.On;
tPngBitmapEncoder.Frames.Add(BitmapFrame.Create(targetBitmap));
tPngBitmapEncoder.Save(tFileStream);
tFileStream.Close();
}
}
}
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