Very Simple Math Question

Very simple math question.

Say I have an image with a point being tracked in it. Here are my variables:

Image Height

Image Width

Point (pixles from left) coordinate X

Point (pixles from top) coordinate Y

For example the wid开发者_开发技巧th, I want it to return a value of -0.5, which represents the distance from the center, such that 1 would be the total right, and -1 would be the total left.

So, how would I calculate so that

The point was (width) a quarter way across the entire frame, or a half way across the left SIDE of the frame. The variables would equal:

Image width: 40

Point X: 10

I know this is basic, but I seriously am having a mind cramp right now O_o.

Thanks,

Christian

Xnew = 2*X/Width - 1
Ynew = 2*Y/Height - 1

Explanation:

X/Width gives you value from 0 (total left) to 1 (total right). 2*X/Width then gives a value from 0 (total left) to 2 (total right). Subtract 1 to get a value from -1 (total left) to 1 (total right).

The same for Y.

If image width is 40, and Point x is 10, then in "your" coordinates PointX will be 0.5 (assuming that coordinates are from -20 to 20). So:

PointX = 1 - 2 * (X / ImageWidth)
PointY = 1 - 2 * (Y / ImageHeight)

Checkout:

PointX = 1 - 2 * (10 / 40) = 0.5 (or 10 pixels to the right side)