CODEWITHSUNDEEP
androidbitmaptransparent
GideonKain
GideonKain

Reputation: 744

android semitransparent bitmap background is black

I'm trying to create semitransparent bitmaps, I used this code:

private Bitmap SemiTransparent(Bitmap bitmap, int opacity) {


    // Create an array to hold the data of bitmap for which semi transparent bitmap is to be obtained
    int[] data = new int[(int)(bitmap.getWidth()) + 1];

    for (int y = 0; y < bitmap.getHeight(); ++y)
    {
           // Get a single line of data
          bitmap.getPixels(data, 0, bitmap.getWidth(), 0, y,bitmap.getWidth(), 1);     

     // Reset the alpha values 
           for (int x = bitmap.getWidth(); x>0; --x) 
           {

                data[x] = (data[x] & 0x00ffffff) | (opacity << 24);
           }     
          //fill alphaBitmap data
           bitmap.setPixels(data, 0, bitmap.getWidth(), 0, y, bitmap.getWidth(), 1);

    }


         return bitmap;
}

The only problem is the background (transparent) color is always black - how can I modify this to make the background Color completely transparent and the rest still semitransparent?

Upvotes: 1

Views: 1645

Answers (1)

balazsbalazs
balazsbalazs

Reputation: 4081

Use this method to make a bitmap transparent:

/**
 * @param bitmap The source bitmap.
 * @param opacity a value between 0 (completely transparent) and 255 (completely
 * opaque).
 * @return The opacity-adjusted bitmap.  If the source bitmap is mutable it will be
 * adjusted and returned, otherwise a new bitmap is created.
 */
private Bitmap adjustOpacity(Bitmap bitmap, int opacity)
{
    Bitmap mutableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
    Canvas canvas = new Canvas(mutableBitmap);
    int colour = (opacity & 0xFF) << 24;
    canvas.drawColor(colour, PorterDuff.Mode.DST_IN);
    return mutableBitmap;
}

See an explanation here: http://blog.uncommons.org/2011/01/12/adjusting-the-opacity-of-an-android-bitmap/

In the blog-post it checks if the bitmap is mutable or not - which can cause problems if the bitmap is mutable but doesn't have the config ARGB_8888 - so use my method instead.

Upvotes: 2

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