The last post of this game development series, I showed you a basic example ShowFPS application that uses a technique called passive rendering.
So In this post, I am gonna show you another example for Active
Rendering. The ShowFPS class from the previous post, has to change to have an active rendering technique.
How to implement active rendering?
The previous
ShowFPS
application redraws itself in the paint() method but it is the swing library that decides when to call
that method.
The event dispatch thread handles the rendering of the swing components and it is out of
your hand.
This is fine for normal applications, it is not recommended for the game though.
Instead
of using event dispatch thread to draw frames, I would rather use a game thread to handle the rendering in a loop on which we'll have full control.
To achieve this ShowFPS class implements the Runnable
interface and The game thread will be created and launched from the
creatAndShowGUI() method.
While the variable running is true gameThread will be running.
Notice that the running is volatile to keep the JVM from making a separate
copy of running variable due to optimization purpose.
So this way changing the variable' s value from other thread will be known to the game thread.
For this application, I didn't use setDefaultCloseOperation() to stop the application instead I added a
windowLinstener to stop it.
Whenever the window is going to close, this event listener will trigger the shutDown
method. This method runs on the EDT(event dispatch thread)and it writes false to running. Before exiting the program it waits for the gameThread to stop.
See code snippet here
The code for updated ShowFPS (ShowFPS to ActiveRendering) application.
Why the fps text is flickering?
If you run the app you see the fps text is flickering. This is because you are seeing two processes first one is clearing the screen with black colour and second is redrawing the contents.
It can be solved if
we don't show the rendering process to the user. I mean we will show only the complete image so the user can't see intermidiate image.
And it is the topic for the next post.
Thanks for reading this one.
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