[Android]如何生成带倒影的Bitmap

public static Bitmap createReflectedImage(Context context, Bitmap originalImage) {  
                   //The gap we want between the reflection and the original image  
                   final int reflectionGap = 4;  
                     
                        int width = originalImage.getWidth(); 
                        int height = originalImage.getHeight(); 
                          
                    
                        //This will not scale but will flip on the Y axis 
                        Matrix matrix = new Matrix(); 
                        matrix.preScale(1, -1); 
                          
                        //Create a Bitmap with the flip matrix applied to it. 
                        //We only want the bottom half of the image 
                        Bitmap reflectionImage = Bitmap.createBitmap(originalImage, 0, height/2, width, height/2, matrix, false); 
                          
                              
                        //Create a new bitmap with same width but taller to fit reflection 
                        Bitmap bitmapWithReflection = Bitmap.createBitmap(width 
                          , (height + height/2), Config.ARGB_8888); 
                        
                       //Create a new Canvas with the bitmap that's big enough for 
                       //the image plus gap plus reflection 
                       Canvas canvas = new Canvas(bitmapWithReflection); 
                       //Draw in the original image 
                       canvas.drawBitmap(originalImage, 0, 0, null); 
                       //Draw in the gap 
                       Paint defaultPaint = new Paint(); 
                       canvas.drawRect(0, height, width, height + reflectionGap, defaultPaint); 
                       //Draw in the reflection 
                       canvas.drawBitmap(reflectionImage,0, height + reflectionGap, null); 
                         
                       //Create a shader that is a linear gradient that covers the reflection 
                       Paint paint = new Paint(); 
                       LinearGradient shader = new LinearGradient(0, originalImage.getHeight(), 0, 
                         bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff, 0x00ffffff, 
                         TileMode.CLAMP); 
                      //Set the paint to use this shader (linear gradient) 
                       paint.setShader(shader); 
                       //Set the Transfer mode to be porter duff and destination in 
                       paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN)); 
                       //Draw a rectangle using the paint with our linear gradient 
                       canvas.drawRect(0, height, width, 
                       bitmapWithReflection.getHeight() + reflectionGap, paint); 
                        
                   return bitmapWithReflection; 
           }