glFrustum describes a perspective matrix that produces a perspective projection.
The current matrix (see glMatrixMode ) is multiplied by this matrix
and the result replaces the current matrix, as if
glMultMatrix were called with the following matrix
as its argument:
.sp 5
.ce
.EQ
down 130 {left ( ~~ matrix {
ccol { {{2 ~ "zNear"} over {"right" - "left"}} above 0 above 0 above 0 }
ccol { 0 above {{2 ~ "zNear"} over {"top" - "bottom"}} ~ above 0 above 0 }
ccol { A ~~~~ above B ~~~~ above C ~~~~ above -1 ~~~~}
ccol { 0 above 0 above D above 0}
} ~~~ right )}
.EN
.sp
.ce
.EQ
down 130
{A ~=~ {"right" + "left"} over {"right" - "left"}}
.EN
.sp
.ce
.EQ
down 130
{B ~=~ {"top" + "bottom"} over {"top" - "bottom"}}
.EN
.sp
.ce
.EQ
down 130
{C ~=~ -{{"zFar" + "zNear"} over {"zFar" - "zNear"}}}
.EN
.sp
.ce
.EQ
down 130
{D ~=~ -{{2 ~ "zFar" ~ "zNear"} over {"zFar" - "zNear"}}}
.EN
.sp
Typically, the matrix mode is GL_PROJECTION , and
(left, bottom, -zNear) and (right, top, -zNear)
specify the points on the near clipping plane that are mapped
to the lower left and upper right corners of the window,
assuming that the eye is located at (0, 0, 0).
-zFar specifies the location of the far clipping plane.
Both zNear and zFar must be positive.
Use glPushMatrix and glPopMatrix to save and restore
the current matrix stack.
GL.glFrontFace()