Game Development: How to add acceleration to velocity?

Question

I have a View which I need to scale with an acceleration, I mean, that when the scale is MIN_SCALE, the velocity must be slow, but when the scale is near of MAX_SALE, the velocity must be more fast. Now my velocity is always the same.

There is a number of frames that the View will use to do it's movement:

numberOfFrames = Math.round((float)ANIMATION_TIME/GameLoopThread.FRAME_PERIOD);
frameCount = 0;

and I calculate the scaleVelocity with that number of frames:

scaleVelocity = (MAX_SCALE-MIN_SCALE)/numberOfFrames;

Each game loop iteration, I update the scale of the view with this code:

if (frameCount<numberOfFrames) {
    currentScale = currentScale + scaleVelocity;
    frameCount++;
}

When frame count has reached the numberOfFrames the animation must end.

How can I add acceleration to this code? take in mind that the acceleration must respect that the view needs to reach the MAX_SCALE at last frame from the frameCount variable.

Rishabh Dhawan · Accepted Answer · 2019-09-28T06:12:15.227

1

Define your interpolator

INTERPOLATOR = new AccelerateInterpolator();

while calculating scaleVelocity, get current interpolated value

float interpolatedValue = INTERPOLATOR.getInterpolation(frameCount / numberOfFrames);

getInterpolation() returns a value between 0(start of animation) and 1(end anim)

scaleVelocity = (MAX_SCALE-MIN_SCALE)/numberOfFrames * interpolatedValue;  // use min,max func if needed.

mathematical equation of accelerate interpolator is f(x) = x², if you want greater change then create your custom interpolator.

working test method for animation.

 private void testAnim() {
    int numberOfFrames = 100;//Math.round((float)ANIMATION_TIME/GameLoopThread.FRAME_PERIOD);
    float frameCount = 0;
    float MAX_SCALE = 4;
    float MIN_SCALE = 0.1f;
    float scaleVelocity;
    float currentScale ;
    Interpolator INTERPOLATOR = new AccelerateInterpolator();

    do {
        float interpolatedValue = INTERPOLATOR.getInterpolation(frameCount / numberOfFrames);
        scaleVelocity = (MAX_SCALE - MIN_SCALE) * interpolatedValue;

        currentScale = Math.max(MIN_SCALE, scaleVelocity);
        ++frameCount;
        Log.d("STACK", "testAnim: currentScale = " + currentScale);
        // apply scale to view.
    } while (frameCount < numberOfFrames);

    // finally set final value of animation.
    currentScale = MAX_SCALE;
    // apply scale to view.

}

edited Sep 28 '19 at 06:12

answered Sep 27 '19 at 19:43

Rishabh Dhawan

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thank you but if I do your logic, it gives a scale between 0.1 and 1.4, something is not working because my MIN_SCALE is 0.1 and MAX_SCALE is 4.0 – NullPointerException Sep 27 '19 at 20:34
I have edited my answer that includes working test method which provides scale values from MIN_SCALE to MAX_SCALE. – Rishabh Dhawan Sep 28 '19 at 06:13
I finally solve it using this formula: currentScale = ((MAX_SCALE-MIN_SCALE)*(scaleInterpolator.getInterpolation((float)(frameCount+1)/numberOfFrames)))+MIN_SCALE; – NullPointerException Sep 28 '19 at 09:42
what do you think about my formula? – NullPointerException Sep 28 '19 at 09:42
that is same logic, except you are adding MIN_SCALE (=0.1)to every frame, you can also try different interpolators. – Rishabh Dhawan Sep 28 '19 at 10:06
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i added MIN_SCALE because if not, always tops in 3.9 instead of 4. Is correct to add it? – NullPointerException Sep 28 '19 at 10:36
Oh yes, I actually ran the code and we need to actually add MIN_SCALE instead of using Math.max(), because we need to animate from MIN_SCALE to MAX_SCALE. – Rishabh Dhawan Sep 28 '19 at 12:59
in your formula,( frameCount+1) is not required, if we stop loop at ( frameCount<=numberOfFrame), it will save an addition op in every loop – Rishabh Dhawan Sep 28 '19 at 13:02

Game Development: How to add acceleration to velocity?

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