package com.gloomyfish.filter.study;
 
import java.awt.image.BufferedImage;
 
public class WaterFilter extends AbstractBufferedImageOp {
 private float wavelength = 16;
 private float amplitude = 10;
 private float phase = 0;
 private float centreX = 0.5f;
 private float centreY = 0.5f;
 private float radius = 50;
 
 private float radius2 = 0;
 private float icentreX;
 private float icentreY;
 
 public WaterFilter() {
 
 }
 
 @Override
 public BufferedImage filter(BufferedImage src, BufferedImage dest) {
 int width = src.getWidth();
  int height = src.getHeight();
 
  if ( dest == null )
   dest = createCompatibleDestImage( src, null );
 
  int[] inPixels = new int[width*height];
  int[] outPixels = new int[width*height];
  getRGB( src, 0, 0, width, height, inPixels );
 icentreX = width * centreX;
 icentreY = height * centreY;
 if ( radius == 0 )
 radius = Math.min(icentreX, icentreY);
 radius2 = radius*radius;
  int index = 0;
  float[] out = new float[2];
  for(int row=0; row<height; row++) {
   for(int col=0; col<width; col++) {
   index = row * width + col;
   
   // 獲取水波的擴散位置，最重要的一步
   generateWaterRipples(col, row, out);
 int srcX = (int)Math.floor( out[0] );
 int srcY = (int)Math.floor( out[1] );
 float xWeight = out[0]-srcX;
 float yWeight = out[1]-srcY;
 int nw, ne, sw, se;
 
 // 獲取周圍四個像素，插值用，
 if ( srcX >= 0 && srcX < width-1 && srcY >= 0 && srcY < height-1) {
  // Easy case, all corners are in the image
  int i = width*srcY + srcX;
  nw = inPixels[i];
  ne = inPixels[i+1];
  sw = inPixels[i+width];
  se = inPixels[i+width+1];
 } else {
  // Some of the corners are off the image
  nw = getPixel( inPixels, srcX, srcY, width, height );
  ne = getPixel( inPixels, srcX+1, srcY, width, height );
  sw = getPixel( inPixels, srcX, srcY+1, width, height );
  se = getPixel( inPixels, srcX+1, srcY+1, width, height );
 }
 
 // 取得對應(yīng)的振幅位置P(x, y)的像素，使用雙線性插值
 /*if(xWeight >=0 || yWeight >= 0)
 {
  outPixels[index] = ImageMath.bilinearInterpolate(xWeight, yWeight, nw, ne, sw, se);  
 }
 else 
 {
  outPixels[index] = inPixels[index];
 }*/
 outPixels[index] = ImageMath.bilinearInterpolate(xWeight, yWeight, nw, ne, sw, se);
   }
  }
 
  setRGB( dest, 0, 0, width, height, outPixels );
  return dest;
 }
 
 private int getPixel(int[] pixels, int x, int y, int width, int height) {
 if (x < 0 || x >= width || y < 0 || y >= height) {
 return 0; // 有點暴力啦，懶得管啦
 }
 return pixels[ y*width+x ];
 }
 
 protected void generateWaterRipples(int x, int y, float[] out) {
 float dx = x-icentreX;
 float dy = y-icentreY;
 float distance2 = dx*dx + dy*dy;
 // 確定 water ripple的半徑，如果在半徑之外，就直接獲取原來位置，不用計算遷移量
 if (distance2 > radius2) { 
 out[0] = x;
 out[1] = y;
 } else {
 // 如果在radius半徑之內(nèi)，計算出來
 float distance = (float)Math.sqrt(distance2);
 // 計算改點振幅
 float amount = amplitude * (float)Math.sin(distance / wavelength * ImageMath.TWO_PI - phase);
 // 計算能量損失， 
 amount *= (radius-distance)/radius; // 計算能量損失，
 if ( distance != 0 )
 amount *= wavelength/distance;
 // 得到water ripple 最終遷移位置
 out[0] = x + dx*amount;
 out[1] = y + dy*amount;
 }
 }
 
}