Question

I’m using Google Maps v2 API for android and I don’t manage to control the transparency of the fillColor.
I would like to be able to see the map under a filled polygon.
Is there a way to do that ?

Thanks for any help !

Answer 1

Well, let me describe how standard 4 bytes color is encoded:

Standard pixel color consists of 4 bytes:

• A (alpha channel) – 0-255 (0 – fully transparent, 255 – fully opaque)
• R (red color channel) – 0-255
• G (green color channel) – 0-255
• B (blue color channel) – 0-255

Each channel represents the saturation of particular color part. So if we need to create fully opaque red color, we need to specify following channel values:

• 255,255,0,0

If we want to make it half-transparent, we need to divide alpha channel value by 2 (255/2 = 127):

• 127,255,0,0

So let’s go back to the android. In Android in most cases you can specify color by specifying it’s hex value:

polygon.setFillColor(0xFF00FF00); //not transparent green color

In hex every channel can be specified by 2 hex digits:

• A(FF)
• R(00)
• G(FF)
• B(00)

If you want to make this color half-transparent, you need to divide FF by 2:

0xFF/2 = 0x7F //the same as 255/2 = 127

polygon.setFillColor(0x7F00FF00); //half-transparent green color

So basically what you need to do – is to play with alpha channel value in order to get transparency you are looking for