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.

SEE ALSO

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