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;}
