Question

I’m animating a UIView by updating its anchorpoint 60 times a second using an NSTimer.
The location of the UIView changes depending on its angle, so it always appears to be down relative to the device…
However, the NSTimer doesn’t fire precisely 60 times a second. It’s always a little off, causing jerky animation. I’ve searched this a lot, I know a bit about delta time, but I don’t know how to apply it to my situation.

Here’s the movement code I’m using:

float rotation = 0;

if (leftSideIsBeingHeldDown) {
    rotation += (0.05f/rotationFactor);
} else if (rightSideIsBeingHeldDown) {
    rotation -= (0.05f/rotationFactor);
}
movementX += -sinf(rotation);
movementY += -cosf(rotation);

float finalX = 0.0001 * movementX;
float finalY = 0.0001 * movementY;

mapView.layer.anchorPoint = CGPointMake(finalX, finalY);

mapView.transform = CGAffineTransformMakeRotation(rotation);

Does anyone know how to apply delta time to this?

Answer 1

You want to record the time you last rotated, and the difference in time between then and now, and use that to work out a factor, which you can use to adjust the rotation and x/y values.

for example:

NSDate now = [NSDate now];
timeDiff = now - lastRotateTime;
factor = timeDiff / expectedTimeDiff;

x = x + xIncrement * factor;
y = y + yIncrement * factor;

angle = angle + angleIncrement * factor;

There are many better examples on game dev forums, which explain it in more detail.