图像处理之水波纹扩散效果(water ripple effect)

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;
            
            // 获取水波的扩散位置，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;
        
        // 获取周围四个像素，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 );
        }
        
        // 取得对应的振幅位置P(x, y)的像素，使用双线性插值
        /*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; // 有点暴力啦，懒得管啦
    }
    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;
    // 确定 water ripple的半径，如果在半径之外，就直接获取原来位置，不用计算迁移量
    if (distance2 > radius2) { 
      out[0] = x;
      out[1] = y;
    } else {
      // 如果在radius半径之内，计算出来
      float distance = (float)Math.sqrt(distance2);
      // 计算改点振幅
      float amount = amplitude * (float)Math.sin(distance / wavelength * ImageMath.TWO_PI - phase);
      // 计算能量损失， 
      amount *= (radius-distance)/radius; // 计算能量损失，
      if ( distance != 0 )
        amount *= wavelength/distance;
      // 得到water ripple 最终迁移位置
      out[0] = x + dx*amount;
      out[1] = y + dy*amount;
    }
  }
  
}