Java的graphics2D fillRect不能正常工作与半透明的颜色

Question

我正在写一个自定义渲染的程序，并需要渲染带边框的矩形。我决定简单地调用graphics2D.fillRect（），切换到边框颜色，并调用graphics2D.drawRect（）。但是，即使我使用相同的坐标和大小背靠背进行调用，但当我绘制的颜色是半透明（具有alpha）时，fillRect（）并不总是填充drawRect包含的整个区域。此外，由fillRect（）绘制的区域有时在drawRect（）所包含的区域之外。为什么这两种方法在不同的地方绘制不同颜色的东西？

下面是一个演示问题的例子。点击窗口中的鼠标将在用alpha和不用绘制填充之间切换。请注意，当使用alpha绘图时，矩形底部有一行像素为白色，但在绘制不带alpha的绘图时，该行像素不在此处。

import java.awt.BasicStroke; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.event.MouseEvent; 
import java.awt.event.MouseListener; 
import java.awt.geom.AffineTransform; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 


public class ColorWithAlpha extends JPanel { 

private boolean hasAlpha = true; 

private static final long serialVersionUID = 1L; 

/** 
* @param args 
*/ 
public static void main(String[] args) { 
    // setup a basic frame with a ColorWithAlpha in it 
    JFrame frame = new JFrame(); 
    JPanel panel = new ColorWithAlpha(); 
    panel.setPreferredSize(new Dimension(500, 500)); 
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    frame.add(panel); 
    frame.pack(); 
    frame.show(); 
} 

public ColorWithAlpha() { 
    super(); 
    setBackground(Color.WHITE); 

    this.addMouseListener(new MouseListener() { 
     @Override 
     public void mouseClicked(MouseEvent arg0) { 
      // when the user clicks their mouse, toggle whether we are drawing a color with alhpa or without. 
      hasAlpha = !hasAlpha; 
      ColorWithAlpha.this.repaint(); 
     } 
     @Override 
     public void mouseEntered(MouseEvent arg0) {} 

     @Override 
     public void mouseExited(MouseEvent arg0) {} 

     @Override 
     public void mousePressed(MouseEvent arg0) {} 

     @Override 
     public void mouseReleased(MouseEvent arg0) {} 
    }); 
} 

@Override 
public void paintComponent(Graphics g) { 
    super.paintComponent(g); 
    Color color = new Color(100, 100, 250);// this color doesnt have an alpha component 

    // some coordinates that demonstrate the bug. Not all combinations of x,y,width,height will show the bug 
    int x = -900; 
    int y = 1557; 
    int height = 503; 
    int width = 502; 
    if (hasAlpha) { // toggle between drawing with alpha and without 
     color = new Color(200, 100, 250, 100); 
    } 
    Graphics2D g2 = (Graphics2D) g; 
    // this is the transform I was using when I found the bug. 
    g2.setTransform(new AffineTransform(0.160642570281124, 0.0, 0.0, -0.160642570281124, 250.0, 488.0)); 


    g2.setColor(color); 
    g2.fillRect(x, y, width, height); 
    g2.setColor(Color.DARK_GRAY); 
    g2.setStroke(new BasicStroke(8f)); 
    g2.drawRect(x, y, width, height); 

} 
} 

Answer 1

废话回答，我重读你的问题并复制你的代码，并找到你在说什么。小的白线是由于绘画中的舍入误差造成的。非常有趣的小问题。在创建Graphics2D之后添加此项

g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, RenderingHints.VALUE_STROKE_PURE); 

渲染提示告诉绘画类您希望某些过程如何工作。我不知道为什么增加颜色的透明度会使舍入不同。我认为它必须与多重渲染提示结合在一起，如抗锯齿。