Fix flashing graphics with double buffering
Yesterday I posted a video of my map editor, which was almost unwatchable because of all the flashing in it. I decided that since I didn't know what was wrong, other people are also having the same problem, and because I am so cool and amazing I will tell you how to fix it.
The flashing occurs when you draw the graphics in steps, for me it was because I was clearing the screen and then drawing the shapes. Which, when the graphics were updated a lot, caused a white flicker when the screen was being cleared.
A solution to the problem is to draw all graphics to a temporary off screen image, and when this is finished draw the image to the screen. This way each time the graphics are drawn, only one image is being drawn and so there will be no flickering.
To accomplish this in Java, I created a temporary Graphics object called tempGraphics and an Image object called offscreenImage. I then assigned the Graphics from the image to the temporary graphics using
tempGraphics = offscreenImage.getGraphics();
This means that whenever anything is drawn to tempGraphics, it is actually drawn to the image, since tempGraphics now points to the images Graphics object.
Now, in the paint method where you would usually draw to the Graphics object passed as a parameter, you instead draw to tempGraphics, so that all graphics are drawn to the offscreen image.
When you are done drawing to the image you draw the image to the screen using the drawImage() method of the Graphics in the paint method.
In case I didn't explain this well, here is some code as an example...
private Graphics tempGraphics;
private Image offscreenImage;
public constructor()
{
...
offscreenImage = createImage(width,height);
tempGraphics = offscreenImage.getGraphics();
...
}
public void paint(Graphics g)
{
tempGraphics.clearRect(0,0,width,height);
tempGraphics.drawSomethingElse();
g.drawImage(offscreenImage,0,0,this);
}
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