CODEWITHSUNDEEP
androidcanvasbitmap
HappyEngineer
HappyEngineer

Reputation: 4055

On an android Canvas, how do I draw overlapping shapes with non-interacting alphas?

On an android Canvas, if I draw a circle with alpha 0xCC and color Color.RED and then draw another circle which partially overlaps the first circle with the same parameters, I'll end up with a venn diagram.

Here is a random example I found (just ignore the [Text] in there). I want to draw overlapping circles like in this diagram, but I don't want the center to be darker, but I do want the whole thing to have alpha so that the map underneath is visible.

Is there a way to do this directly or do I need to draw to a bitmap without alpha and then set the alpha for the whole bitmap and draw it to a canvas? (I haven't used bitmaps yet, so I am not sure how they are used yet.)

Upvotes: 1

Views: 2985

Answers (1)

Will Kru
Will Kru

Reputation: 5212

The easy way would be your suggested solution, ie. drawing all circles with no alpha to a bitmap, then draw that bitmap to another one using the desired alpha. The hard way would be using blend modes, specifically PorterDuff.Mode in Android. An example can be found here.

Upvotes: 3

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