hey all,

i'm working on a (mostly) 2d game, but in 3d space...so everything is at y=0, camera is at (0,800,0) looking down.  my question is how can i get the 3d coordinates of the boundaries of what is visible?  specifically, if an object is at y=0, what are the maximum and minimum x and z values that are within the camera's view volume?  of course, i need to account for varying resolutions, etc, so trial and error isn't a good option :)

i'm sure there's an easy solution, but i'm not seeing it.

thanks,
mike

It is really just basic trigonometry, assuming your floor is flat at y=0

You need to have the height and the angle, so you need to get the length of the hypotenuse, which can be attained by:
(1/cos(FOV/2))*height
That will get the height of the viewable rectangle. To get the width, just multiply it by the aspect ratio.
The FOV and Aspect Ratio come from your Projection Matrix and the height, you said was 800. So just plug it in and go!

Louis Ingenthron:

It is really just basic trigonometry, assuming your floor is flat at y=0

You need to have the height and the angle, so you need to get the length of the hypotenuse, which can be attained by:
(1/cos(FOV/2))*height
That will get the height of the viewable rectangle. To get the width, just multiply it by the aspect ratio.
The FOV and Aspect Ratio come from your Projection Matrix and the height, you said was 800. So just plug it in and go!

the thing that's messing me up is the resolution, which isn't in that equation.   basically, 1280x720 will have a bigger viewable area than 640-480.  or am i rethinking things?

Think about a first person shooter. When you go up in resolution, does your view become wider? Nope, you just get more detail. How much you actually see is set in the projection matrix, which doesn't change with the resolution (except for aspect ratio).

fair enough.

thanks for the help...feel pretty dumb now :) .