NAME

vpWindow - multiply the projection matrix by a perspective or orthographic matrix

SYNOPSIS

#include <volpack.h>

vpResult

vpWindow(vpc, type, left, right, bottom, top, near, far)

: vpContext *vpc;
: int type;
: double left, right;
: double bottom, top;
: double near, far;

ARGUMENTS

vpc: VolPack context from vpCreateContext.
type: Projection type code. Currently, must be VP_PARALLEL.
left: Coordinate of the left vertical clipping plane.
right: Coordinate of the right vertical clipping plane.
bottom: Coordinate of the bottom horizontal clipping plane.
top: Coordinate of the top horizontal clipping plane.
near: Coordinate of the near depth clipping plane.
far: Coordinate of the far depth clipping plane.

DESCRIPTION

vpWindow is used to multiply the current projection matrix by a perspective or orthographic projection matrix. The new projection matrix is defined by the coordinates of six clipping planes in the eye coordinate system (see vpCurrentMatrix(3)). The matrix maps the points (left, bottom, near) and (right, top, near) to the lower left and upper right corners of the clipping window. For an alternative means of specifying the projection matrix, see vpWindowPHIGS(3).

Currently, only orthographic projections are supported. Perspective projections will be added in a future release.

The matrix for parallel projections is:

: A 0 0 D
0 B 0 E
0 0 C F
0 0 0 1
A = 2 / (right - left)
B = 2 / (top - bottom)
C = 2 / (far - near)
D = (left + right) / (left - right)
E = (bottom + top) / (bottom - top)
F = (near + far) / (near - far)

The matrix is multiplied into the projection matrix, even if the projection matrix is not the current matrix. By default, the matrix is post-multiplied (N = N*m where N is the current matrix and m is the argument to vpMultMatrix). The VP_CONCAT_MODE option to vpSeti can be used to select pre-multiplication. The default window is a parallel projection with left = bottom = near = -0.5, and right = top = far = 0.5.

STATE VARIABLES

The current matrix concatenation parameters can be retrieved with the following state variable codes (see vpGeti(3)): VP_CONCAT_MODE.

ERRORS

The normal return value is VP_OK. The following error return values are possible:

VPERROR_BAD_VALUE: The clipping plane coordinates are invalid (left >= right, etc.).
VPERROR_BAD_OPTION: The type argument is invalid.