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In OpenGL, to keep program rendering frames I need a while loop, all the code that put inside the loop is executed every loop. The loop looks like this:

while(!glfwWindowShouldClose(window))
{
    // Check and call events
    glfwPollEvents();

    // Rendering commands here
    ...

    // Swap the buffers
    glfwSwapBuffers(window);
}

Now I'm jumping into OpenGL ES and trying to learn from this example:

https://github.com/googlesamples/android-ndk/tree/master/gles3jni

However, I couldn't find any while or for loop in the code. Instead, There're something else likes extending the GLSurfaceView and implementing the GLSurfaceView.Renderer. I don't really get how it works.

Therefore, I wonder how the iteration goes every time it render a frame? Is every thing written in the .cpp file executed every loop or just functions that being called by the JNI? And once It finish rendering the very first frame, where does it start at the beginning of the 2nd loop? Your attention and help is very much appreciated.

Toan Tran
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1 Answers1

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In Android, you do not need to do the looping yourself - the rendering loop is managed for you by the OS. It is implemented in GLSurfaceView.Renderer, which calls onDrawFrame which is called each frame, you just need to override this method in your renderer. It is all done in the Java code - if you wish to implement your OpenGL ES code in cpp, you create a rendering method in your JNI code and call it from your overridden onDrawFrame, like it is done in the project you are looking at.

yakobom
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  • So If I have a variable ``x`` that needed to be changed every frame, I could only put it in the method (``step()`` method in the above example), which is called through JNI from ``onDrawFrame``, is that correct? – Toan Tran Feb 23 '17 at 05:51
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    Yes, you got it. If this variable is cpp, then you update it in 'step', if it is Java, you update it in 'onDrawFrame' – yakobom Feb 23 '17 at 06:16
  • Glad to help. Good luck! – yakobom Feb 23 '17 at 06:17
  • I have another question here :http://stackoverflow.com/questions/42358194/how-to-debug-android-studio-project-using-ndk-and-jni-line-by-line-to-see-the. It would be great if you could take sometime to have a look at it. I would appreciate that. – Toan Tran Feb 23 '17 at 06:32