perspective Subroutine

Purpose

Defines a perspective projection transformation.

Libraries

Graphics Library

C (libgl.a)

FORTRAN (libfgl.a)

C Syntax

void   perspective
(Angle fovy, 
Float32 aspect, 
Coord near, Coord far)

FORTRAN Syntax

SUBROUTINE PERSPE(fovy, aspect, near, far)
INTEGER*4 fovy
REAL aspect, near, far

Description

The perspective subroutine defines a perspective projection transformation by specifying a viewing pyramid in the eye coordinate system. The pyramid comprises:

• The field-of-view angle in the y direction of the eye coordinate system
• The aspect ratio that determines the field-of-view in the x direction
• The distance to the near and far clipping planes in the z direction.

The field of view is the range of the area that is being viewed. The aspect ratio is the ratio of x (width) to y (height), and 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 has the same aspect ratio as the frustum, it displays the image without distortion.

The perspective subroutine is very similar to the window subroutine. The only difference between these two is the manner in which the parameters specify the viewing frustum.

After the perspective subroutine completes, the eye coordinate system is set up so that x is to the right, y is up, and z is towards the viewer (out of the screen).

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

Parameters

Example

The example C language program zbuffer1.c uses the perspective subroutine to load a projection transformation as the current transformation matrix.

Implementation Specifics

This subroutine is part of GL in the AIXwindows Environment/6000 Version 1, Release 2 with AIXwindows/3D Feature.

Files

Related Information

Defining a 3-D orthographic transformation with the ortho subroutine.

Defining a 2-D orthographic transformation with the ortho2 subroutine.

Defining a perspective projection transformation in terms of x and y coordinates with the window subroutine.

AIX Graphics Library Overview and Working with Coordinate Systems.