Java-在paintComponent中合成的圆角面板

根据原始问题（如下），我现在提供以下赏金：

基于

AlphaComposite

的圆角解决方案

• 请用

  JPanel

  演示
• 角落必须是完全透明的
• 必须能够支持JPG绘画，但仍有圆角
• 不得使用setClip（或任何剪辑）
• 必须有体面的表现

希望有人能很快学会，这似乎很容易

如果有一个很好的理由解释为什么这件事永远做不到，并且其他人也同意，我也会奖励奖金

下面是我想到的示例图像（但使用

AlphaComposite

）

---

原始问题

我一直在试图找到一种使用合成来实现圆角的方法，非常类似于或

但是，我在没有中间BuffereImage的情况下尝试的结果是无效的——四舍五入的目标组合显然不会影响源。我尝试过不同的方法，但都不管用。应该是一个圆形的红色矩形，而不是正方形

所以，我有两个问题，真的：

1） 有没有办法让这一切顺利进行

2） 中间映像实际上会产生更好的性能吗

SSCCE：

测试面板t面板

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JLabel;

public class TPanel extends JLabel {
int w = 300;
int h = 200;

public TPanel() {
    setOpaque(false);
    setPreferredSize(new Dimension(w, h));
        setMaximumSize(new Dimension(w, h));
        setMinimumSize(new Dimension(w, h));
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g.create();

    // Yellow is the clipped area.
    g2d.setColor(Color.yellow);
    g2d.fillRoundRect(0, 0, w, h, 20, 20);
    g2d.setComposite(AlphaComposite.Src);

    // Red simulates the image.
    g2d.setColor(Color.red);
    g2d.setComposite(AlphaComposite.SrcAtop);

    g2d.fillRect(0, 0, w, h);
    }
}

以及它的沙箱

import java.awt.Dimension;
import java.awt.FlowLayout;

import javax.swing.JFrame;

public class Sandbox {
public static void main(String[] args) {
    JFrame f = new JFrame();
        f.setMinimumSize(new Dimension(800, 600));
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new FlowLayout());

        TPanel pnl = new TPanel();
        f.getContentPane().add(pnl);

        f.setVisible(true);
    }
}

---

我已经研究过这个问题，但无法在对系统类的单个调用中看到如何做到这一点

Graphics2D是一个抽象实例，实现为SunGraphics2D。例如，源代码可以在上获得，因此我们可以通过复制一些代码来“做相同的事情，但不同”。但是，绘制图像的方法取决于某些“管道”类，这些类不可用。虽然你做了一些关于类加载的事情，但是你可能会碰到一些本机的、优化的类，这些类不能被操作来实现理论上的最优方法；你所得到的只是把图像画成正方形

但是，我们可以采用一种方法，使我们自己的非本机（读：慢？）代码尽可能少地运行，并且不取决于图像大小，而是取决于圆形矩形中（相对）较低的区域。而且，不复制内存中的图像，会消耗大量内存。但是，如果您有大量内存，那么显然，在创建实例之后，缓存的映像会更快

备选案文1：

import java.awt.Composite;
import java.awt.CompositeContext;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;

import javax.swing.JLabel;

public class TPanel2 extends JLabel implements Composite, CompositeContext {
private int w = 300;
private int h = 200;

private int cornerRadius = 20;
private int[] roundRect; // first quadrant
private BufferedImage image;
private int[][] first = new int[cornerRadius][];
private int[][] second = new int[cornerRadius][];
private int[][] third = new int[cornerRadius][];
private int[][] forth = new int[cornerRadius][];

public TPanel2() {
    setOpaque(false);
    setPreferredSize(new Dimension(w, h));
    setMaximumSize(new Dimension(w, h));
    setMinimumSize(new Dimension(w, h));

    // calculate round rect     
    roundRect = new int[cornerRadius];
    for(int i = 0; i < roundRect.length; i++) {
        roundRect[i] = (int)(Math.cos(Math.asin(1 - ((double)i)/20))*20); // x for y
    }

    image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB); // all black
}

@Override
public void paintComponent(Graphics g) {
    // discussion:
    // We have to work with the passed Graphics object.

    if(g instanceof Graphics2D) {

        Graphics2D g2d = (Graphics2D) g;

        // draw the whole image and save the corners
        g2d.setComposite(this);
        g2d.drawImage(image, 0, 0, null);
    } else {
        super.paintComponent(g);
    }
}

@Override
public CompositeContext createContext(ColorModel srcColorModel,
        ColorModel dstColorModel, RenderingHints hints) {
    return this;
}

@Override
public void dispose() {

}

@Override
public void compose(Raster src, Raster dstIn, WritableRaster dstOut) {
    // lets assume image pixels >> round rect pixels
    // lets also assume bulk operations are optimized

    // copy current pixels
    for(int i = 0; i < cornerRadius; i++) {
        // quadrants

        // from top to buttom
        // first
        first[i] = (int[]) dstOut.getDataElements(src.getWidth() - (cornerRadius - roundRect[i]), i, cornerRadius - roundRect[i], 1, first[i]);

        // second
        second[i] = (int[]) dstOut.getDataElements(0, i, cornerRadius - roundRect[i], 1, second[i]);

        // from buttom to top
        // third
        third[i] = (int[]) dstOut.getDataElements(0, src.getHeight() - i - 1, cornerRadius - roundRect[i], 1, third[i]);

        // forth
        forth[i] = (int[]) dstOut.getDataElements(src.getWidth() - cornerRadius + roundRect[i], src.getHeight() - i - 1, cornerRadius - roundRect[i], 1, forth[i]);
    }

    // overwrite entire image as a square
    dstOut.setRect(src);

    // copy previous pixels back in corners
    for(int i = 0; i < cornerRadius; i++) {
        // first
        dstOut.setDataElements(src.getWidth() - cornerRadius + roundRect[i], i, first[i].length, 1, second[i]);

        // second
        dstOut.setDataElements(0, i, second[i].length, 1, second[i]);

        // third
        dstOut.setDataElements(0, src.getHeight() - i - 1, third[i].length, 1, third[i]);

        // forth
        dstOut.setDataElements(src.getWidth() - cornerRadius + roundRect[i], src.getHeight() - i - 1, forth[i].length, 1, forth[i]);
    }
}

}

导入java.awt.Composite；
导入java.awt.CompositeContext；
导入java.awt.Dimension；
导入java.awt.Graphics；
导入java.awt.Graphics2D；
导入java.awt.RenderingHints；
导入java.awt.image.buffereImage；
导入java.awt.image.ColorModel；
导入java.awt.image.graster；
导入java.awt.image.WritableRaster；
导入javax.swing.JLabel；
公共类TPanel2扩展了JLabel，实现了复合的CompositeContext{
私人int w=300；
私有int h=200；
专用半径=20；
private int[]roundRect；//第一象限
私有缓冲图像；
private int[][]first=新int[cornerRadius][]；
私有整数[][]秒=新整数[cornerRadius][]；
私有int[]third=新int[cornerRadius][]；
私有整数[][]第四=新整数[cornerRadius][]；
公共TPanel2（）{
设置不透明（假）；
设置首选尺寸（新尺寸（w，h））；
设置最大尺寸（新尺寸（w，h））；
设置最小尺寸（新尺寸（w，h））；
//计算圆矩形
roundRect=新整数[cornerRadius]；
for（int i=0；i>圆形矩形像素
//我们还假设批量操作已优化
//复制当前像素
对于（int i=0；i

备选案文2：

import java.awt.AlphaComposite;
import java.awt.Composite;
import java.awt.CompositeContext;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;
import javax.swing.JLabel;

public class TPanel extends JLabel implements Composite, CompositeContext {
private int w = 300;
private int h = 200;

private int cornerRadius = 20;
private int[] roundRect; // first quadrant
private BufferedImage image;

private boolean initialized = false;
private int[][] first = new int[cornerRadius][];
private int[][] second = new int[cornerRadius][];
private int[][] third = new int[cornerRadius][];
private int[][] forth = new int[cornerRadius][];

public TPanel() {
    setOpaque(false);
    setPreferredSize(new Dimension(w, h));
    setMaximumSize(new Dimension(w, h));
    setMinimumSize(new Dimension(w, h));

    // calculate round rect     
    roundRect = new int[cornerRadius];
    for(int i = 0; i < roundRect.length; i++) {
        roundRect[i] = (int)(Math.cos(Math.asin(1 - ((double)i)/20))*20); // x for y
    }

    image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB); // all black
}

@Override
public void paintComponent(Graphics g) {
    if(g instanceof Graphics2D) {

        Graphics2D g2d = (Graphics2D) g;

        // draw 1 + 2 rectangles and copy pixels from image. could also be 1 rectangle + 4 edges
        g2d.setComposite(AlphaComposite.Src);

        g2d.drawImage(image, cornerRadius, 0, image.getWidth() - cornerRadius - cornerRadius, image.getHeight(), null);
        g2d.drawImage(image, 0, cornerRadius, cornerRadius, image.getHeight() - cornerRadius - cornerRadius, null);
        g2d.drawImage(image, image.getWidth() - cornerRadius, cornerRadius, image.getWidth(), image.getHeight() - cornerRadius, image.getWidth() - cornerRadius, cornerRadius, image.getWidth(), image.getHeight() - cornerRadius, null);

        // draw the corners using our own logic
        g2d.setComposite(this);

        g2d.drawImage(image, 0, 0, null);

    } else {
        super.paintComponent(g);
    }
}

@Override
public CompositeContext createContext(ColorModel srcColorModel,
        ColorModel dstColorModel, RenderingHints hints) {
    return this;
}

@Override
public void dispose() {

}

@Override
public void compose(Raster src, Raster dstIn, WritableRaster dstOut) {
    // assume only corners need painting

    if(!initialized) {
        // copy image pixels
        for(int i = 0; i < cornerRadius; i++) {
            // quadrants

            // from top to buttom
            // first
            first[i] = (int[]) src.getDataElements(src.getWidth() - cornerRadius, i, roundRect[i], 1, first[i]);

            // second
            second[i] = (int[]) src.getDataElements(cornerRadius - roundRect[i], i, roundRect[i], 1, second[i]);

            // from buttom to top
            // third
            third[i] = (int[]) src.getDataElements(cornerRadius - roundRect[i], src.getHeight() - i - 1, roundRect[i], 1, third[i]);

            // forth
            forth[i] = (int[]) src.getDataElements(src.getWidth() - cornerRadius, src.getHeight() - i - 1, roundRect[i], 1, forth[i]);
        }
        initialized = true;
    }       

    // copy image pixels into corners
    for(int i = 0; i < cornerRadius; i++) {
        // first
        dstOut.setDataElements(src.getWidth() - cornerRadius, i, first[i].length, 1, second[i]);

        // second
        dstOut.setDataElements(cornerRadius - roundRect[i], i, second[i].length, 1, second[i]);

        // third
        dstOut.setDataElements(cornerRadius - roundRect[i], src.getHeight() - i - 1, third[i].length, 1, third[i]);

        // forth
        dstOut.setDataElements(src.getWidth() - cornerRadius, src.getHeight() - i - 1, forth[i].length, 1, forth[i]);
    }
}

}

导入java.awt.AlphaComposite；
导入java.awt.Composite；
导入java.awt.CompositeContext；
导入java.awt.Dimens