Convert JPanel to image

Question

Is there a way to convert a JPanel (that has not yet been displayed) to a BufferedImage?

thanks,

Jeff

Answer 1

Take a look at BasicTableUI. The cell renderer is drawn on image without showing and then drawn on visible table component.

Answer 2

The answer from Tom is basically correct, but invoke paint() directly is not recommended, as it is a synchronous call and can interrupt with other operation on the swing thread. Instead of using paint(), we should use print() instead

public BufferedImage createImage(JPanel panel) {

    int w = panel.getWidth();
    int h = panel.getHeight();
    BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    Graphics2D g = bi.createGraphics();
    panel.print(g);
    g.dispose();
    return bi;
}

Answer 3

Basically I'm building a component that needs to get written to an image but not displayed

ScreenImage explains how to do what you want.

---

Relevant section of ScreenImage.java (slightly edited). layoutComponent forces all buttons appear in the image.

/**
 * @return Renders argument onto a new BufferedImage
 */
public BufferedImage createImage(JPanel panel, int width, int height) {
    BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g = bi.createGraphics();
    panel.setSize(width, height); // or panel.getPreferedSize()
    layoutComponent(panel);
    panel.print(g);
    g.dispose();
    return bi;
}

private void layoutComponent(Component component) {
    synchronized (component.getTreeLock()) {
        component.doLayout();

        if (component instanceof Container) {
            for (Component child : ((Container) component).getComponents()) {
                layoutComponent(child);
            }
        }
    }
}

Answer 4

From the BufferedImage you can create a graphics object, which you can use to call paint on the JPanel, something like:

public BufferedImage createImage(JPanel panel) {

    int w = panel.getWidth();
    int h = panel.getHeight();
    BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    Graphics2D g = bi.createGraphics();
    panel.paint(g);
    g.dispose();
    return bi;
}

You may need to make sure you set the size of the panel first.