How Can I Make The Background Of My Custom Brush Transparent?

I wanted to draw on the canvas with the code below with my custom brush, but as you can see in the picture, the background of my brush is black, albeit without color. Although I sp

Solution 1:

The reason it happens is because Paint doesn't have an alpha composing mode set by default. Thus, when you're trying to paint a bitmap over your canvas it will replace the destination pixels with your brush pixels, which in your case is #00000000. And that will result in pixel being displayed as black. Have a look into this documentation: https://developer.android.com/reference/android/graphics/PorterDuff.Mode

By the first glance it seems you're looking for PorterDuff.Mode.SRC_OVER or PorterDuff.Mode.SRC_ATOP - this way transparent pixels from your source image (your brush) will not over-draw the pixels from your destination (canvas). In case your background is always non-transparent, you will see no difference between SRC_OVER and SRC_ATOP, but if it isn't - choose the one which fits your needs. Then you can modify setupPathAndPaint method by adding this line to its end:

    mDrawPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OVER));