Choppy animation in android OpenGL Game Loop

[Stephen Bell]

Hi all

Really hoping someone can help me out here. I've written an android Open GL ES 2.0 game and my logic update calls and rendering calls are running on the GL Rendering thread. I'm also using a fixed time delta, not variable.

The code for my loop is below. The problem is that the animation just isn't smooth. It will run for a second or 2 smoothly, then it will become 'choppy' for a little while, then return to normal.

The 'choppiness' is present if the sprite is moving fast or slow, but is a lot more noticeable with faster moving sprites.

I have 2 test devices, a Google Nexus 10 running KitKat and an old Samsung Galaxy Ace running Gingerbread. Now, if I change my 'maxFramesSkip' value from 5 to 1 it runs perfectly on my Nexus 10, however, on the Galaxy Ace, it seems to speed up and slow down, so I changed it back to 5. At andvalue other than 1, the animation is choppy.

I've tried interpolation but this has no effect. I've included my code here for that too.

I can't understand why this is happening. I should point out that my rendering takes a maxumum of 14ms to complete and the logic updates take a maximum of 4ms to complete. So there should be no frame skipping. I'm therefore wondering if there is something wrong with my loop? I'v spent literally months trying various things, but nothing produces smoother animation. So i'm hoping someone with a better understanding of game loops can help me out!!

Any help would be apprecated!

Main Game Loop

    float interpolation;
    long nextGameTick = System.currentTimeMillis();
	//loop counter
	int loops;
	//This is the amount of frames that we allow our app to skip before logic updating is affected (generally shouldn't happen)
	final int maxFrameskip = 5;								
	//Game updates per second
	final int ticksPerSecond = 60;
	//Amount of time each update should take		
	final int skipTicks = (1000 / ticksPerSecond);

    public void onDrawFrame(GL10 gl) {
		
		
		//Set/Re-set loop back to 0 to start counting again
		loops=0;
		
		while(System.currentTimeMillis() > nextGameTick && loops < maxFrameskip){
		
			SceneManager.getInstance().getCurrentScene().updateLogic();
			nextGameTick+=skipTicks;
			timeCorrection += (1000d/ticksPerSecond) % 1;
			nextGameTick+=timeCorrection;
			timeCorrection %=1;
			loops++;
			tics++;

		}

                interpolation = (float)(System.currentTimeMillis() + skipTicks - nextGameTick)
	              / (float)skipTicks; 
				
		render(interpolation);
    }

Interpolation in render()

 render(float interpolation){
    
        //This example shows interpolation for X axis only.  Y position (spriteScreenY is assumed to be valid)
        interpolatedPosX = spriteGridX+(SpriteXVelocity*dt)*interpolation;
        spriteScreenPosX = interpolationPosX * screenWidth;
 
        drawSprite(spriteScreenX, spriteScreenY);			


    }