I know this seems really easy, but I just can''t remember how. If I have a point ( x, y ), how can a find the angle with respect to the origin point ( 0, 0 )? Something like atan( y / x ) will work for most angles, but not all ( when x = 0 for example ). I''m sure there''s a way to do this.

atan2(x,y)

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Stolen from Magmai Kai Holmlor, who held it from Oluseyi, who was inspired by Kylotan...

a point doesn''t have an angle with another point. 2 points make a line

but i think you mean find the angle between the line (0,0 to x,y) with the x axis.

which is just a simple vector equation:

you need 2 vectors. one vector is x,y the other on the x axis lets choose 1,0

so you do:

invcos [ ((x,y) dot (1,0)) / ( |(x,y)| * |(1,0)| ) ]

definition of dot product:
http://www.geocities.com/SiliconValley/2151/math2d.html

basically:
(x,y) dot (1,0) = x * 1 + y * 0

and |(x,y)| is the magnitude of vector x,y which is:
sqrt(x^2 + y^2)


also try looking here:
http://www.geocities.com/SiliconValley/Horizon/6933/3d.html

they have a description as well further down the page (search for the text "find the angle between the normal and the light")