Question

我在WPF中有一个Image控件，其中包含一个包含大量透明像素的图像。现在，每当我在MouseDown控件的完整矩形区域内单击时，Image上的Image事件就会触发。我想要一些方法来检测鼠标是否发生在图像的不透明部分。

这样做的最佳方式是什么？

Answer 1

使用this answer中的技术，您可以从Image派生，以创建OpaqueClickableImage，只响应图像的非透明区域中的点击测试：

public class OpaqueClickableImage : Image
{
    protected override HitTestResult HitTestCore(PointHitTestParameters hitTestParameters)
    {
        var source = (BitmapSource)Source;

        // Get the pixel of the source that was hit
        var x = (int)(hitTestParameters.HitPoint.X / ActualWidth * source.PixelWidth);
        var y = (int)(hitTestParameters.HitPoint.Y / ActualHeight * source.PixelHeight);

        // Copy the single pixel into a new byte array representing RGBA
        var pixel = new byte[4];
        source.CopyPixels(new Int32Rect(x, y, 1, 1), pixel, 4, 0);

        // Check the alpha (transparency) of the pixel
        // - threshold can be adjusted from 0 to 255
        if (pixel[3] < 10)
            return null;

        return new PointHitTestResult(this, hitTestParameters.HitPoint);
    }
}

添加此类后，只需像常规图像一样使用它：

<utils:OpaqueClickableImage Name="image" Source="http://entropymine.com/jason/testbed/pngtrans/rgb8_t_bk.png" Stretch="None"/>

Answer 2

public class OpaqueClickableImage : Image
{
    protected override HitTestResult HitTestCore(PointHitTestParameters hitTestParameters)
    {
        var source = (BitmapSource)Source;
        var x = (int)(hitTestParameters.HitPoint.X / ActualWidth * source.PixelWidth);
        var y = (int)(hitTestParameters.HitPoint.Y / ActualHeight * source.PixelHeight);
        if (x == source.PixelWidth)
            x--;
        if (y == source.PixelHeight)
            y--;
        var pixels = new byte[4];
        source.CopyPixels(new Int32Rect(x, y, 1, 1), pixels, 4, 0);
        if (pixels[3] < 1) return null;
        return new PointHitTestResult(this, hitTestParameters.HitPoint);
    }
}

WPF：检测图像仅在非透明部分上单击

2 个答案: