Android的半透明位图的背景是黑色的 [英] android semitransparent bitmap background is black

问题描述

我试图创建半透明位图，我用这个code：

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;
}

唯一的问题是背景（透明）的颜色总是黑色的 - 我怎么能修改此使背景色彩完全透明的，其余仍半透明

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?

推荐答案

使用这个方法做一个透明位图：

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;
}

在这里看到一个解释：
的http://blog.uncommons.org/2011/01/12/adjusting-the-opacity-of-an-android-bitmap/

在博客-后，检验该位是可变的或不 - 这可能会导致问题，如果该位是可变的，但是不具备的配置ARGB_8888 - 所以用我的方法，而不是

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.

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