perspective(3G)

NAME
     perspective - defines a perspective projection transformation

C SPECIFICATION
     void perspective(fovy, aspect, near, far)
     Angle fovy;
     float aspect;
     Coord near, far;

PARAMETERS
     fovy     expects the field-of-view angle in the y direction.  The field
              of view is the range of the area that is being viewed.  fovy
              must be > 2 or an error results.

     aspect   expects the aspect ratio which determines the field of view in
              the x direction.  The aspect ratio is the ratio of x (width) to
              y (height).

     near     expects the distance from the viewer to the closest clipping
              plane (always positive).

     far      expects the distance from the viewer to the farthest clipping
              plane (always positive).

DESCRIPTION
     perspective specifies a viewing pyramid into the world coordinate system.
     In general, the aspect ratio in perspective should match the aspect ratio
     of the associated viewport.  For example, aspect=2.0 means the viewer's
     angle of view is twice as wide in x as it is in y.  If the viewport is
     twice as wide as it is tall, it displays the image without distortion.

     When the system is in single matrix mode, perspective loads a matrix onto
     the transformation stack, replacing the current top matrix.  When the
     system is in viewing, projection, or texture matrix mode, perspective
     replaces the current Projection matrix and leaves the ModelView matrix
     stack and the Texture matrix unchanged.

SEE ALSO
     mmode, ortho, viewport, window