Finding points on a rectangle at a given angle

Question

I\'m trying to draw a gradient in a rectangle object, with a given angle (Theta), where the ends of the gradient are touching the perimeter of the rectangle.

Answer 1

Following your picture, I'm going to assume that the rectangle is centered at (0,0), and that the upper right corner is (w,h). Then the line connecting (0,0) to (w,h) forms an angle φ with the X axis, where tan(φ) = h/w.

Assuming that θ > φ, we are looking for the point (x,y) where the line that you have drawn intersects the top edge of the rectangle. Then y/x = tan(θ). We know that y=h so, solving for x, we get x = h/tan(θ).

If θ < φ, the line intersects with the right edge of the rectangle at (x,y). This time, we know that x=w, so y = tan(θ)*w.