Why is my deltaTime in my GameLoop 0?

Question

I have a question about my code. I wrote a basic GameLoop for an Android Game and while testing it I realized the deltaTime is always 0.

The code looks like this:

@Override
 public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        lastTime = System.currentTimeMillis();
    }

@Override
    public void onDrawFrame(GL10 gl) {
        float currTime = System.currentTimeMillis();
        float deltaTime = currTime - lastTime;
        float msPerFrame = 1000.0f/ 60.0f;

        if(deltaTime < msPerFrame){
            try {
                Thread.sleep((long)(msPerFrame-deltaTime));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        update(deltaTime, gl);
        lastTime = currTime;

    }

    public void update(float deltaTime, GL10 gl){
           //doStuff
    }

lastTime and currTime are always the same and the deltaTime is 0. I don't know if this is right or the code is just wrong but I think the deltaTime shouldn't be 0...

I test the app with Android Studios Emulator.

Answer 1

All those time functions work with the datatype long. Try changing float to long to avoid potential rounding errors.

currentTimeMillis() might not be accurate enough. Try System.nanoTime() instead: https://stackoverflow.com/questions/351565/system-currenttimemillis-vs-system-nanotime