Question

I am writing a mapping application in Java, using Swing for the UI (I’ve included a prototype drawing at the end of this post). The map is implemented using a custom MapPanel class that extends JPanel. The map is fetched from the server as a series of 300×300 images (tiles) that are painted on the MapPanel whenever its paintMap() method is called. Due to the length and complexity (multiple classes, etc.) of the code I can’t include all of it here but the paintMap() method basically works like this:

// Loop for each map tile (image, xPos, yPos)
getGraphics().drawImage(image, xPos, yPos, 300, 300, null);

I would like to have another JPanel (containing a JSlider for zoom control) overlayed on top of the map panel, but I’m having difficulties getting this to work. Whenever I paint the map, the overlayed JPanel disappears. If I repaint the overlayed JPanel in the paintMap() method, it flickers badly when the map is being dragged (and thus repainted continuously).

Any suggestions for how I could implement my UI without flickering?

Answer 1

getGraphics().drawImage(image, xPos, yPos, 300, 300, null); // WRONG!!

1. Don’t call getGraphics() – instead override the paintComponent(Graphics) of a JPanel or JComponent and paint when requested to do so.
2. Use this as the ImageObserver