In the following reproducer, I am reproducing what I'm seeing in the graphical interface.
I'd like to repaint a dirty region of a canvas (a JPanel), because a full repaint introduces more latencies.
However when the repaint (dirty rectangle) function is invoked, it causes some issues with nested Graphics2D objects. In particular
This code may mis-use clip bounds, but I wasn't expecting this "artifact" upon the creation of the sub (nested) graphic context.
What would be the proper way to deal with clips, nested graphic contexts, and the dirty region (or rectangle) repaint in this situation.
My intuition tells me the code should compute its shape without using the clipping area.
import javax.swing.*;
import java.awt.*;
import java.awt.geom.Rectangle2D;
public class Reproducer {
public static void main(String[] args) {
var comp = new MyJPanel();
var timer = new Timer(2_000, e -> {
SwingUtilities.invokeLater(comp::bug);
});
timer.start();
timer.setRepeats(true);
SwingUtilities.invokeLater(() -> {
var frame = new JFrame("Reproducer");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(new Dimension(300, 300));
frame.setVisible(true);
frame.getContentPane().add(comp);
});
}
private static class MyJPanel extends JPanel {
public MyJPanel() {
setSize(600, 600);
setPreferredSize(getSize());
}
@Override
protected void paintComponent(Graphics g) {
var g2 = (Graphics2D) g;
super.paintComponent(g2);
g2.setColor(Color.cyan);
g2.fill(g2.getClip());
var graphicsBox = (Graphics2D) g2.create(10, 10, 290, 290);
var clipBounds = graphicsBox.getClipBounds();
graphicsBox.setColor(Color.LIGHT_GRAY);
graphicsBox.setStroke(new BasicStroke(2));
graphicsBox.drawRect(clipBounds.x, clipBounds.y, clipBounds.width, clipBounds.height);
graphicsBox.setColor(Color.red);
graphicsBox.fill(new Rectangle2D.Double(clipBounds.x 2,
clipBounds.y 2,
clipBounds.width - 2,
clipBounds.height - 2));
graphicsBox.dispose();
var graphicsOverlay = (Graphics2D) g2.create(100, 100, 100, 100);
graphicsOverlay.setColor(Color.YELLOW);
graphicsOverlay.fillOval(10, 10, 60, 60);
graphicsOverlay.dispose();
}
public void bug() {
getVisibleRect();
repaint(100, 100, 100, 100);
}
}
}
EDIT by moving the fill above drawRect
CodePudding user response：
So, there are a couple of "mistakes"
I found this...
graphicsBox.drawRect(clipBounds.x, clipBounds.y, clipBounds.width, clipBounds.height);
graphicsBox.setColor(Color.red);
graphicsBox.fill(new Rectangle2D.Double(clipBounds.x 2,
clipBounds.y 2,
clipBounds.width - 2,
clipBounds.height - 2));
to be a little erroneous, which meant when a clip was applied, the background area was not been filled properly.
The call to super.paintComponent was filling the clip area with the background color of the component, but graphicsBox.fill wasn't filling the entire area, allow part of the background color to be seen.
I also found the result of Graphics2D#create(int, int, int, int) to be a little surprising
The new Graphics object has its origin translated to the specified point (x, y). Its clip area is determined by the intersection of the original clip area with the specified rectangle.
(emphasis added by me)
I mean, honestly, I shouldn't be surprised, but I've just never used these features before so it took me a little by surprise.
So, I corrected the graphicsBox rendering code so that the fill will fill the entire clipping area first and THEN the rectangle is drawn (within the bounding rectangle)
var graphicsBox = (Graphics2D) g2.create(10, 10, 290, 290);
var clipBounds = graphicsBox.getClipBounds();
graphicsBox.setColor(Color.red);
graphicsBox.fill(new Rectangle2D.Double(clipBounds.x,
clipBounds.y,
clipBounds.width,
clipBounds.height));
Collections.shuffle(colors);
graphicsBox.setColor(colors.get(0));
graphicsBox.setStroke(new BasicStroke(2));
graphicsBox.drawRect(clipBounds.x 1, clipBounds.y 1, clipBounds.width - 2, clipBounds.height - 2);
graphicsBox.dispose();
nb: The reference to colors is just a list of Colors which I randomise during the paint process, so I can "see" what's going on
Another trick might be to change the background color of the component to make it easier to "see" where things are been updated incorrectly.
When you have issues like this, it's really important to reduce the amount of clutter to see if you can narrow down the problem, I took out most of the paint code to figure out all these "little" things which were combining to give you issues.
Runnable example...
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
var comp = new MyJPanel();
var timer = new Timer(2_000, e -> {
SwingUtilities.invokeLater(comp::bug);
});
timer.start();
timer.setRepeats(true);
SwingUtilities.invokeLater(() -> {
var frame = new JFrame("Reproducer");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(new Dimension(300, 300));
frame.setVisible(true);
frame.getContentPane().add(comp);
});
}
private static class MyJPanel extends JPanel {
private List<Color> colors;
public MyJPanel() {
setSize(600, 600);
setPreferredSize(getSize());
colors = Arrays.asList(new Color[] {
Color.BLACK,
Color.BLUE,
Color.CYAN,
Color.DARK_GRAY,
Color.GRAY,
Color.GREEN,
Color.LIGHT_GRAY,
Color.MAGENTA,
Color.ORANGE,
Color.PINK,
Color.RED,
Color.WHITE,
Color.YELLOW
});
}
@Override
protected void paintComponent(Graphics g) {
var g2 = (Graphics2D) g;
super.paintComponent(g2);
g2.setColor(Color.cyan);
g2.fill(g2.getClip());
var graphicsBox = (Graphics2D) g2.create(10, 10, 290, 290);
var clipBounds = graphicsBox.getClipBounds();
graphicsBox.setColor(Color.red);
graphicsBox.fill(new Rectangle2D.Double(clipBounds.x,
clipBounds.y,
clipBounds.width,
clipBounds.height));
Collections.shuffle(colors);
graphicsBox.setColor(colors.get(0));
graphicsBox.setStroke(new BasicStroke(2));
graphicsBox.drawRect(clipBounds.x 1, clipBounds.y 1, clipBounds.width - 2, clipBounds.height - 2);
graphicsBox.dispose();
var graphicsOverlay = (Graphics2D) g2.create(100, 100, 100, 100);
graphicsOverlay.setColor(Color.YELLOW);
graphicsOverlay.fillOval(10, 10, 60, 60);
graphicsOverlay.dispose();
}
public void bug() {
getVisibleRect();
repaint(100, 100, 100, 100);
}
}
}
If you're having "performance" issues, you might consider using a BufferedImage as the primary canvas and update it, then simply paint the image.
Alternatively, it might be time to move over to using BufferStrategy, this is going to get you as close to the "metal" as Java/Swing allows