有过UI设计经验的一定对2D图形渲染中的Color Gradient 或多或少有些接触，很多编程
语言也提供了Gradient的接口，但是想知道它是怎么实现的嘛？
本文介绍三种简单的颜色梯度变化算法，就可以很容易实现常见的梯度变化算法
三种都要求提供两个参数即起始颜色RGB值, 最终颜色RGB的值。
垂直梯度颜色变化，效果如下：
水平梯度颜色变化，效果如下：
水平与垂直两个方向叠加梯度变化效果如下：
算法代码及其解释
计算起始颜色和终点颜色RGB之间差值代码如下：
float rr = startColor[0] - endColor[0];
float gg = startColor[1] - endColor[1];
float bb = startColor[2] - endColor[2];
实现垂直梯度变化的代码如下：
r = endColor[0] + (int)(rr * ((float)row/255.0f) +0.5f);
g = endColor[1] + (int)(gg * ((float)row/255.0f) +0.5f);
b = endColor[2] + (int)(bb * ((float)row/255.0f) +0.5f);
实现水平梯度变化代码如下：
// set gradient color valuefor each pixel
r = endColor[0] + (int)(rr * ((float)col/255.0f) +0.5f);
g = endColor[1] + (int)(gg * ((float)col/255.0f) + 0.5f);
b = endColor[2] + (int)(bb * ((float)col/255.0f) +0.5f);
实现水平和垂直两个方向上Gradient叠加代码如下：
r = endColor[0] + (int)(rr * (((float)col * (float)row)/size) +0.5f);
g = endColor[1] + (int)(gg * (((float)col * (float)row)/size) +0.5f);
b = endColor[2] + (int)(bb * (((float)col * (float)row)/size) +0.5f);
程序对上面三种Gradient方法分别放在三个不同的方法中，根据参数调用。
程序的完全Java源代码如下：
- import java.awt.BorderLayout;
- import java.awt.Dimension;
- import java.awt.Graphics;
- import java.awt.Graphics2D;
- import java.awt.RenderingHints;
- import java.awt.image.BufferedImage;
- import javax.swing.JComponent;
- import javax.swing.JFrame;
- public class ColorGradientDemo extends JComponent {
- /**
- *
- */
- private static final long serialVersionUID = -4134440495899912869L;
- private BufferedImage image = null;
- protected void paintComponent(Graphics g) {
- Graphics2D g2 = (Graphics2D)g;
- g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
- g2.drawImage(getImage(4), 5, 5, image.getWidth(), image.getHeight(), null);
- }
- public BufferedImage getImage(int type) {
- if(image == null) {
- image = new BufferedImage(256, 256, BufferedImage.TYPE_INT_ARGB);
- int[] rgbData = new int[256*256];
- if(type == 1) {
- generateVGradientImage(rgbData);
- } else if(type == 2) {
- generateHGradientImage(rgbData);
- } else {
- generateHVGradientImage(rgbData);
- }
- setRGB(image, 0, 0, 256, 256, rgbData);
- }
- return image;
- }
- private void generateVGradientImage(int[] rgbData) {
- int[] startColor = getStartColor();
- int[] endColor = getEndColor();
- float rr = startColor[0] - endColor[0];
- float gg = startColor[1] - endColor[1];
- float bb = startColor[2] - endColor[2];
- int a=255;
- int r=0, g=0, b=0;
- int index = 0;
- for(int row=0; row<256; row++) {
- for(int col=0; col<256; col++) {
- // set random color value for each pixel
- // set gradient color value for each pixel
- r = endColor[0] + (int)(rr * ((float)row/255.0f) + 0.5f);
- g = endColor[1] + (int)(gg * ((float)row/255.0f) + 0.5f);
- b = endColor[2] + (int)(bb * ((float)row/255.0f) + 0.5f);
- rgbData[index] = ((a & 0xff) << 24) |
- ((r & 0xff) << 16) |
- ((g & 0xff) << 8) |
- ((b & 0xff));
- index++;
- }
- }
- }
- private void generateHGradientImage(int[] rgbData) {
- int[] startColor = getStartColor();
- int[] endColor = getEndColor();
- float rr = startColor[0] - endColor[0];
- float gg = startColor[1] - endColor[1];
- float bb = startColor[2] - endColor[2];
- int a=255;
- int r=0, g=0, b=0;
- int index = 0;
- for(int row=0; row<256; row++) {
- for(int col=0; col<256; col++) {
- // set gradient color value for each pixel
- r = endColor[0] + (int)(rr * ((float)col/255.0f) + 0.5f);
- g = endColor[1] + (int)(gg * ((float)col/255.0f) + 0.5f);
- b = endColor[2] + (int)(bb * ((float)col/255.0f) + 0.5f);
- rgbData[index] = ((a & 0xff) << 24) |
- ((r & 0xff) << 16) |
- ((g & 0xff) << 8) |
- ((b & 0xff));
- index++;
- }
- }
- }
- private void generateHVGradientImage(int[] rgbData) {
- int[] startColor = getStartColor();
- int[] endColor = getEndColor();
- float rr = startColor[0] - endColor[0];
- float gg = startColor[1] - endColor[1];
- float bb = startColor[2] - endColor[2];
- int a=255;
- int r=0, g=0, b=0;
- int index = 0;
- float size = (float)Math.pow(255.0d, 2.0);
- for(int row=0; row<256; row++) {
- for(int col=0; col<256; col++) {
- // set random color value for each pixel
- r = endColor[0] + (int)(rr * (((float)col * (float)row)/size) + 0.5f);
- g = endColor[1] + (int)(gg * (((float)col * (float)row)/size) + 0.5f);
- b = endColor[2] + (int)(bb * (((float)col * (float)row)/size) + 0.5f);
- rgbData[index] = ((a & 0xff) << 24) |
- ((r & 0xff) << 16) |
- ((g & 0xff) << 8) |
- ((b & 0xff));
- index++;
- }
- }
- }
- public int[] getStartColor() {
- return new int[]{246,53,138};
- }
- public int[] getEndColor() {
- return new int[]{0,255,255};
- }
- public void setRGB( BufferedImage image, int x, int y, int width, int height, int[] pixels ) {
- int type = image.getType();
- if ( type == BufferedImage.TYPE_INT_ARGB || type == BufferedImage.TYPE_INT_RGB )
- image.getRaster().setDataElements( x, y, width, height, pixels );
- else
- image.setRGB( x, y, width, height, pixels, 0, width );
- }
- public static void main(String[] args) {
- JFrame frame = new JFrame("Gradient Color Panel");
- frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
- frame.getContentPane().setLayout(new BorderLayout());
- // Display the window.
- frame.getContentPane().add(new ColorGradientDemo(), BorderLayout.CENTER);
- frame.setPreferredSize(new Dimension(280,305));
- frame.pack();
- frame.setVisible(true);
- }
- }
