Bitmap上下合成图片
合成两张图片，上下叠加的效果：
/**
* 把两个位图覆盖合成为一个位图，以底层位图的长宽为基准
*
* @param backBitmap 在底部的位图
* @param frontBitmap 盖在上面的位图
* @return
*/
public static Bitmap mergeBitmap(Bitmap backBitmap, Bitmap frontBitmap) {
if (backBitmap == null || backBitmap.isRecycled()
|| frontBitmap == null || frontBitmap.isRecycled()) {
return null;
}
Bitmap bitmap = backBitmap.copy(Bitmap.Config.ARGB_8888, true);
Canvas canvas = new Canvas(bitmap);
Rect baseRect = new Rect(0, 0, backBitmap.getWidth(), backBitmap.getHeight());
Rect frontRect = new Rect(0, 0, frontBitmap.getWidth(), frontBitmap.getHeight());
canvas.drawBitmap(frontBitmap, frontRect, baseRect, null);
return bitmap;
}
