如何在Swing中仅重绘脏区？

Question

1. Does repainting dirty region only improve performance?

2. If the answer is yes, how to do it? Originally I use repaint() to call paintComponent(Graphics); however, recently I aware that repaint() is actually repaint(0,0,width,height), which repaints everything each time. If I use repaint() with parameters to specify the dirty region, in what way will it pass such data to paintComponent(Graphics)?

Answer 1

If I use repaint() with parameters to specify the dirty region, in what way will it pass such data to paintComponent(Graphics)?

The "clip bounds" or the Graphics object will be set to the specified region

1.Does repainting dirty region only improve performance?

Why? Do you have a painting problem. Don't micro optimize the code, unless you have a reason to do so. The code will be harder to maintain and debug. You will be adding extra logic to determine which regions need to be repainted.

Also, remember that multiple repaint requests get merged into a single request. So if you make a request to repaint the top/left corner of a component and the immediately request a repaint of the bottom/right, these two request will be merged into an area that includes both regions, which means the entire component will be repainted. So you have done extra work for nothing.

Answer 2

To repaint only "dirty" regions of a large JComponent you will need to use the RepaintManager . You can get the current RepaintManager with:

RepaintManager rm = RepaintManager.currentManager(component);

You can even replace the RepaintManager with your own custom version. Additional details can be found on Oracle 's website.