Darken parts of a free-hand cropped image in android

问题

I want to add a free hand crop functionality.

Till now I can open the picture and draw a path around the part of the image that I want to crop thanks to this code:

https://stackoverflow.com/a/18459072/2361533

But before opening the cropped image in another activity, I want to darken the outside part of the crop path, to show the user how the cropped image will be. In case he does not like the result, he could reset the image.

It would be something like the image here: Android: Free Croping of Image

How can i do this ?

回答1:

Use the following two methods as a start:

setXfermode(new PorterDuffXfermode(Mode.DARKEN)); 
canvas.clipPath(path, Region.Op.DIFFERENCE);

The first one is applied to a Paint object and darkens a certain region. The second "clips" the path in your canvas and takes the inverse (using Region.Op.DIFFERENCE).

来源：https://stackoverflow.com/questions/22912712/darken-parts-of-a-free-hand-cropped-image-in-android