WPF：检测图像仅在非透明部分上单击 [英] WPF: Detect Image click only on non-transparent portion

问题描述

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，每当我在图像上的 MouseDown 事件就会触发>图像控制。我想用某种方法检测鼠标是否发生在图像的不透明部分。

I have an Image control in WPF which contains an image with lots of transparent pixels. Right now, the MouseDown event on Image fires whenever I click within the full rectangular region of the Image control. I would like some way to detect if the mouse click occurred on a nontransparent portion of the image.

这样做的最佳方法是什么？

What would be the best way of doing this?

推荐答案

使用这个答案你可以从 Image 派生来创建一个 OpaqueClickableImage 只响应图像的足够不透明区域中的命中测试：

Using the technique in this answer you can derive from Image to create an OpaqueClickableImage that only responds to hit-testing in sufficiently non-transparent areas of the image:

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，只需像常规一样使用它image：

after adding this class, just use it like a regular image:

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

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