Wednesday, July 26, 2006

Java SE 6.0 has smoother rendering

Prior to Java SE 6.0, there were some issues with Swing painting.
  • When a minimized swing window was unobscured, it took a while for it to repaint. Till then the user saw a gray box. I think they also call it the "gray rect" problem :-)
  • Assume that the application is blocking the event dispatch thread (maybe because it is performing a large computation or loading a large file...). If we minimize and application, then it will not show a painted window upon unobscuring untill the event dispatch thread is unblocked. (offcourse we should not block the event dispatch thread for such a large task. Ideally a task larger than 250 ms should be started in a seperate thread)
In Java SE 6.0 these issues are resolved with "true double buffering". Java maintains a buffer that keeps an image of the onscreen window. This buffer is updated whenever the contents of the onscreen window are changed. If we minimize and then maximize the window, the window will not be repainted from scratch, instead it's image from the buffer will be copied to the video memory (using the toolkit thread). This elliminates the "gray rect" problem since the window will be displayed immediately without any time lag. Since the buffer is maintained in the hardware (most likely video RAM), it is true double buffering.

I am not very certain what a toolkit thread is. Will find out, but in the meanwhile if anyone knows, please post a comment.

The fine print:
True double buffering is enabled only on the windows platform at the moment. However it is implemented for other platforms as well, and will be enabled soon.

2 comments:

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