Java animation stutters when not moving mouse cursor

Question

I have a quite simple animation, a text in a big font moving continuously (pixel by pixel) to the left. The text is first converted to an image, then a timer task is started

Answer 1

Profiling shows that you are saturating the shared thread used by javax.swing.Timer. One mitigation strategy is to use a longer period and/or a larger increment/decrement, as shown here.

Addendum: In addition, you are laboriously re-rendering the entire image in each call to paintComponent(). Instead, render it once using TextLayout, seen here, and draw() only the newly visible portion each time.

Answer 2

Try calling this method when you are done drawing:

 Toolkit.getDefaultToolkit().sync();

This flushs the graphics buffer which some systems like Linux use. See the Javadoc: http://docs.oracle.com/javase/7/docs/api/java/awt/Toolkit.html#sync()

Answer 3

• Don't, EVER, use getGraphics and you should NEVER call paintComponent yourself, this not how custom painting is done in Swing. Instead, update the state and call repaint.
• Don't rely on magic numbers, use the information you have at hand (getWidth and getHeight)
• Swing components are doubled buffered, so it's unlikely you would need to create you own buffered strategy. This simple act could be slowing down your painting
• You must call super.paintComponent. This is even more important with JComponent, as it is not opaque and failing to do so could result in some nasty paint artefacts.
• You should override JComponent#getPreferredSize so it can work with layout managers for efficiently.
• You may find a shorter delay produces a better illusion, say 40 milliseconds (roughly 25fps) for example

Take a look at Swing animation running extremely slow, which through some object management and optimisation, was able to increase from 500 animated objects up to 4500.

Also take a look at Performing Custom Painting and Painting in AWT and Swing in particular

Answer 4

Problem solved!

To answer my own question: After realizing that any continuous input (mouse or keyboard) makes the animation run smoothly, I remembered that inputs can be generated by the program itself, using an object of the class java.awt.Robot. That lead to a simple workaround: Create a Robot and let it press a key or a mouse move in each animation cycle.

final Robot robot = new Robot();
javax.swing.Timer timer = new javax.swing.Timer(initialDelay, new ActionListener()
{
    public void actionPerformed(ActionEvent e)
    {
        // update your image...

        robot.keyPress(62);
     }
});

This is a kludge, but works perfectly.