Question

I’m programming a flash game, I made an array of points (x and y positions) that some movieclips must follow. Those movieclips have a certain speed (they make steps of 5 pixels for now). When I want to move them horizontally or vertically, everything’s fine, I have to add or remove 5 pixels of those clips’ x or y. But sometimes they have to move diagonally and now that’s complicated.

What I’m doing:

var angle:Number = Math.atan2(nextPoint.y - this.y, nextPoint.x - this.x) * 180 / Math.PI;
var xstep:Number = Math.cos(angle) * this.speed;
var ystep:Number = Math.sqrt(Math.pow(this.speed, 2) - Math.pow(xstep, 2));

this.x += xstep;
this.y += ystep;

It’s only a fraction of the code, but I think it’s all you need.
Basically, this makes my movieclip do a little step (of this.speed (currently set to 5) pixels).

If the current point and the next point have the same y position, it works fine. When they don’t, it doesn’t work. The angle is right at first but it slowly decreases (while it should stay the same). I don’t know if it’s the angle that isn’t computed the right way or if it’s the x and y steps, but it’s one of those, I’m sure.

Answer 1

Try this instead:

var angle:Number = Math.atan2(nextPoint.y - this.y, nextPoint.x - this.x);
var xstep:Number = Math.cos(angle) * this.speed;
var ystep:Number = Math.sin(angle) * this.speed;

Because cos operates on angles in radians, you don’t need to convert to degrees. Computing the y component of an angle uses sin, so it should be similar to x. I’m not able to test this, but it’s possible that ystep will be backwards and may need to be multiplied by -1.