Manipulate alpha bytes of Java/Android color int
Check out the Color class.
Your code would look a bit something like this.
int color = 0xFFFFFFFF;
int transparent = Color.argb(0, Color.red(color), Color.green(color), Color.blue(color));
So wrapping it in a method might look like:
@ColorInt
public static int adjustAlpha(@ColorInt int color, float factor) {
int alpha = Math.round(Color.alpha(color) * factor);
int red = Color.red(color);
int green = Color.green(color);
int blue = Color.blue(color);
return Color.argb(alpha, red, green, blue);
}
And then call it to set the transparency to, let's say, 50%:
int halfTransparentColor = adjustAlpha(0xFFFFFFFF, 0.5f);
I think using the provided Color class is a little bit more self-documenting that just doing the bit manipulation yourself, plus it's already done for you.
Use ColorUtils#setAlphaComponent in the android-support-v4.
in the android-support-v4:
int alpha = 85; //between 0-255
@ColorInt
int alphaColor = ColorUtils.setAlphaComponent(Color.Red, alpha);
An alternative is:
int myOpaqueColor = 0xffffffff;
byte factor = 20;// 0-255;
int color = ( factor << 24 ) | ( myOpaqueColor & 0x00ffffff );
Or using float:
int myOpaqueColor = 0xffffffff;
float factor = 0.7f;// 0-1;
int color = ( (int) ( factor * 255.0f ) << 24 ) | ( myOpaqueColor & 0x00ffffff);
You can change any channel by changing the bitwise value 24
.
public final static byte ALPHA_CHANNEL = 24;
public final static byte RED_CHANNEL = 16;
public final static byte GREEN_CHANNEL = 8;
public final static byte BLUE_CHANNEL = 0;
// using:
byte red = 0xff;
byte green = 0xff;
byte blue = 0xff;
byte alpha = 0xff;
int color = ( alpha << ALPHA_CHANNEL ) | ( red << RED_CHANNEL ) | ( green << GREEN_CHANNEL ) | ( blue << BLUE_CHANNEL );// 0xffffffff