## table of contents

vpWindow(3) | Library Functions Manual | vpWindow(3) |

# 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 1A = 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.

# SEE ALSO¶

VolPack(3), vpCreateContext(3), vpCurrentMatrix(3), vpWindowPHIGS(3)

VolPack |