I have a frustum with
left = -2,
right = 2,
close = 0.5,
far = 10.
I've put the eye of the camera in
(0, 0, -2.5)looking directly at
(0, 0, 0) with up
(0, 1, 0).
Suppose I want to place an object centered on
z = -1. I want to find the
X coordinate so that under this trunk appears exactly centered on the left edge of the screen.
I set up the following diagram to help me:
+ z | | / -X<_______________|______/__________>X __ x__ | -one / | / | / l_ | __ / a | / | close to dist = n = 0.5 | / | | -2.5 | -z
X I can use trig trigonometry simple. As
tan a = l / n Y
tan a = x / 1.5 then the formula for
x = l / n * 1.5 = 2 / 0.5 * 1.5 = 6.
But when I use this value of x to draw an object to the left of the center, it does not appear centered at the edge of the screen. What am I doing wrong?