Cocos2d Sprite Movement Speed

Question

I have a class which creates a sprite at a random point on the screen, this sprite then moves to the center of the screen.

How can I make it so that it always travels at the same speed?

obviously

CCMoveTo* move = [CCMoveTo actionWithDuration:5 position: ccp(screenWidth/2, screenHeight/2)];

Will always mean the duration is 5 seconds regardless of the distance. But I want the speed to be constant if its travelling 50 pixels or 500 pixels.

Any Help much appreciated

Answer 1

Calculate the duration from the distance to the center.

duration = distance / rate;

Say that moving 50 pixels in 5 seconds is okay. Then your rate is 10 pixels/second.

rate = 10;

If your sprite is at (x,y) then distance is by the pythagorean theorem

dx = x - screenWidth / 2;
dy = y - screenHeight / 2;
distance = sqrt(dx * dx + dy * dy);