AWT custom rendering - capture smooth resizes and eliminate resize flicker

Question

I've been looking at this for several months and so far this is the best I have come up with.

The structure (render outside of EDT) is not up for debate, as our application operates this way and will not be rewritten. The application has a layout model and a scripting model which are integrated and drive rendering, so the render must be performed outside of the AWT paint model.

What I am trying to arrive at is the optimal and reliable way to perform custom rendering.

The following SSCCE works fairly well for us. However, during frame resizes, it has 2 drawbacks:

• There is occasional flicker, especially on rapid resizes
• The "smooth resize" hack which is to invoke resize (via checkSize here) from a paint() call only works well for expansions. When reducing the frame it usually does not render until the mouse button is released
• Also, but not so evident here, it does throw occasional IllegalStateExceptions - is it OK to simply catch/ignore these?

Also useful is input on whether this is the optimal approach for a custom render path that takes place outside of the EDT. I have tried most, and done fairly extensive research. This combination (backbuffer image, double buffer strategy) seems to work the best.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferStrategy;

public class SmoothResize extends Frame implements ComponentListener, MouseMotionListener {

    public SmoothResize() {
        addComponentListener(this);
        addMouseMotionListener(this);
    }

    private boolean sizeChanged = false;
    private Dimension old = new Dimension(0, 0);
    private synchronized void checkSize(String source) {
        int width = getWidth();
        int height = getHeight();
        if (old.width == width && old.height == height)
            return;
        sizeChanged = true;
        String type =
            (old.width > width && old.height > height) ? "shrink" :
                (old.width < width && old.height < height) ? "expand" : "resize";
        System.out.println(source + " reports " + type + ": "+getWidth()+", "+getHeight());
        old.setSize(width, height);
    }

    public void componentResized(ComponentEvent arg0) { checkSize("componentResized"); }
    public void mouseMoved(MouseEvent e) { checkSize("mouseMoved"); }
    public void paint(Graphics g) { checkSize("paint"); }
    public void update(Graphics g) { paint(g); }

    public void addNotify() {
        super.addNotify();
        createBufferStrategy(2);
    }

    private synchronized void render() {
        BufferStrategy strategy = getBufferStrategy();
        if (strategy==null || !sizeChanged) return;
        sizeChanged = false;
        // Render single frame
        do {
            // The following loop ensures that the contents of the drawing buffer
            // are consistent in case the underlying surface was recreated
            do {
                System.out.println("render");
                Graphics draw = strategy.getDrawGraphics();
                Insets i = getInsets();
                int w = getWidth()-i.left-i.right;
                int h = getHeight()-i.top-i.bottom;
                draw.setColor(Color.YELLOW);
                draw.fillRect(i.left, i.top+(h/2), w/2, h/2);
                draw.fillRect(i.left+(w/2), i.top, w/2, h/2);
                draw.setColor(Color.BLACK);
                draw.fillRect(i.left, i.top, w/2, h/2);
                draw.fillRect(i.left+(w/2), i.top+(h/2), w/2, h/2);
                draw.dispose();

                // Repeat the rendering if the drawing buffer contents 
                // were restored
            } while (strategy.contentsRestored());

            // Display the buffer
            strategy.show();

            // Repeat the rendering if the drawing buffer was lost
        } while (strategy.contentsLost());
    }

    public static void main(String[] args) {
        Toolkit.getDefaultToolkit().setDynamicLayout(true);
        System.setProperty("sun.awt.noerasebackground", "true");
        SmoothResize srtest = new SmoothResize();
        //srtest.setIgnoreRepaint(true);
        srtest.setSize(100, 100);
        srtest.setVisible(true);
        while (true) {
            srtest.render();
        }
    }

    public void componentHidden(ComponentEvent arg0) { }
    public void componentMoved(ComponentEvent arg0) { }
    public void componentShown(ComponentEvent arg0) { }

    public void mouseDragged(MouseEvent e) { }
}

Answer 1

This answer is left here for reference, but is not the correct answer because it renders inside the EDT thread.

Here is a working fix! :D Basically the problem is that the ComponentResized is not appropriately called until the mouse is released after a shrink. Also, because the paint and checkSize methods are synchronized, they can exclude each other in rare instances. The fix is to override the validate method in the Frame class. This method is always called if the Frame changes state, including shrinks and growths. So we simply have to check the size in the validate and we can actually completely forget about using a ComponentResized method at all.

So, here is working code that compiles as is. I changed some of the variable names to improve my personal readability.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.image.BufferStrategy;
import java.awt.Frame;

public class SmoothResize extends Frame {

public static void main(String[] args) {
    Toolkit.getDefaultToolkit().setDynamicLayout(true);
    System.setProperty("sun.awt.noerasebackground", "true");
    SmoothResize srtest = new SmoothResize();
    //srtest.setIgnoreRepaint(true);
    srtest.setSize(100, 100);
    srtest.setVisible(true);
}

public SmoothResize() {
    render();
}

private Dimension old_size = new Dimension(0, 0);
private Dimension new_size = new Dimension(0, 0);

public void validate() {
    super.validate();
    new_size.width = getWidth();
    new_size.height = getHeight();
    if (old_size.equals(new_size)) {
        return;
    } else {
        render();
    }
}

public void paint(Graphics g) {
    validate();
}

public void update(Graphics g) {
    paint(g);
}

public void addNotify() {
    super.addNotify();
    createBufferStrategy(2);
}

protected synchronized void render() {
    BufferStrategy strategy = getBufferStrategy();
    if (strategy == null) {
        return;
    }
    // Render single frame
    do {
        // The following loop ensures that the contents of the drawing buffer
        // are consistent in case the underlying surface was recreated
        do {
            Graphics draw = strategy.getDrawGraphics();
            Insets i = getInsets();
            int w = (int)(((double)(getWidth() - i.left - i.right))/2+0.5);
            int h = (int)(((double)(getHeight() - i.top - i.bottom))/2+0.5);
            draw.setColor(Color.YELLOW);
            draw.fillRect(i.left, i.top + h, w,h);
            draw.fillRect(i.left + w, i.top, w,h);
            draw.setColor(Color.BLACK);
            draw.fillRect(i.left, i.top, w, h);
            draw.fillRect(i.left + w, i.top + h, w,h);
            draw.dispose();

            // Repeat the rendering if the drawing buffer contents 
            // were restored
        } while (strategy.contentsRestored());

        // Display the buffer
        strategy.show();

        // Repeat the rendering if the drawing buffer was lost
    } while (strategy.contentsLost());
   }

  }

I hope that works for you!

Also, last second edit, I changed the logical ternary operation for the selection of your shrink or expand String. The last comparison was unnecessary because for the comparison in question, the values can be greater than, less than or equal to each other. There is not another possibility that would not generate a NullPointerException.

The stricken text is no longer relevant as I have completely removed that entire method. I indicate the other changes I've made to the original post as comments.

Answer 2

Here is code that renders with an outside Thread doing all the work. It does this by being able to render anything that implements the Renderable interface. I have tested this with both Swing and AWT (JFrame and Frame) and it works with no flickering. Note, it does flicker if you implement onto a JRootPane and set that pane as the JFrame's root pane. This has to do with how the component is buffered, and could be fixed if that is how you want to use this.

If this is still not what you were looking for, just say and I'll give it another go. This is actually fun, as it has been awhile since I've done any Java GUI work.

Anyways, here you go:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Toolkit;
import javax.swing.JFrame;

public class SmoothResize extends Frame implements Renderable {

    public static void main(String[] args) {
        Toolkit.getDefaultToolkit().setDynamicLayout(true);
        System.setProperty("sun.awt.noerasebackground", "true");
        SmoothResize srtest = new SmoothResize();
        RenderThread renderThread = new RenderThread(srtest);
        renderThread.start();
        srtest.setSize(100, 100);
        srtest.setVisible(true);
    }

    public SmoothResize() {
    }

    public void addNotify() {
        super.addNotify();
        createBufferStrategy(2);
    }

    @Override
    public Dimension getSize() {
        return new Dimension(getWidth(), getHeight());
    }

    @Override
    public Graphics acquireGraphics() {
        return this.getGraphics();
    }
}

class RenderThread extends Thread {

    Renderable target;
    Dimension last_size = new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE);

    public RenderThread(Renderable d) {
        if (d == null) {
            throw new NullPointerException("Drawable target cannot be null.");
        }
        target = d;

    }

    @Override
    public void run() {
        while (true) {
            render(false);
        }
    }

    private synchronized void render(boolean force) {
        Dimension size;
        do {
            size = target.getSize();
            if (size == null) {
                return;
            }

            Graphics draw = target.acquireGraphics();
            if (draw == null) {
                return;
            }
            draw.setPaintMode();
            int w = (int) (((double) (size.width)) / 2 + 0.5);
            int h = (int) (((double) (size.height)) / 2 + 0.5);
            draw.setColor(Color.YELLOW);
            draw.fillRect(0, h, w, h);
            draw.fillRect(w, 0, w, h);
            draw.setColor(Color.BLACK);
            draw.fillRect(0, 0, w, h);
            draw.fillRect(w, h, w, h);
            draw.dispose();
            // Repeat the rendering if the target changed size
        } while (!size.equals(target.getSize()));
    }
}

interface Renderable {

    public Graphics acquireGraphics();

    public Dimension getSize();
}