NAME

       vpCurrentMatrix - choose the current transformation matrix

SYNOPSIS

       #include <volpack.h>

       vpResult
       vpCurrentMatrix(vpc, option)
           vpContext *vpc;
           int option;

ARGUMENTS

       vpc    VolPack context from vpCreateContext.

       option A code specifying one of the VolPack transformation matrices (VP_MODEL, VP_VIEW or VP_PROJECT).

DESCRIPTION

       vpCurrentMatrix is used to choose the current transformation matrix.  The option parameter must be one of
       the following: VP_MODEL       modeling transformation
       VP_VIEW        viewing transformation
       VP_PROJECT     projection   transformation  Subsequent  calls  to  the  matrix  transformation  functions
       (vpIdentityMatrix, vpTranslate, vpRotate, vpScale, vpMultMatrix and vpSetMatrix) are applied to  the  new
       current transformation matrix.

       Typically  the  modeling  transformation  is  used to specify a transformation from object coordinates to
       world coordinates.  In object coordinates the volume data is located inside a unit cube centered  at  the
       origin  (corners  at (-0.5, -0.5, -0.5) and (0.5, 0.5, 0.5)).  The default modeling transformation is the
       identity, so the volume is initially located inside the unit cube in world coordinates.  By default,  the
       current  matrix is VP_MODEL.  The modeling transformation is also applied to light direction vectors (see
       vpSetLight(3)).

       The viewing transformation is used for transforming world  coordinates  into  eye  coordinates.   In  eye
       coordinates  the  viewer  is looking down the Z axis in the negative direction.  The default value of the
       matrix is also the identity, so the viewer is looking down the Z  axis  in  world  coordinates  as  well.
       Typically  this transformation matrix is used to specify the location and direction of the viewer.  It is
       also possible to combine the modeling and viewing matrices (as in the OpenGL  viewing  model),  in  which
       case  you  can  store  the  composite transformation in either the model or the view matrix set the other
       matrix to the identity.

       The projection transformation specifies the transformation from eye coordinates to clip coordinates.   In
       the clip coordinate system the entire viewing frustum lies inside a cube defined by the planes X=1, X=-1,
       Y=1,  Y=-1, Z=1 and Z=-1.  This transformation also specifies the type of projection used to produce a 2D
       image.  The 2D image is computed by projecting along the Z axis in the clip coordinate  system  and  then
       scaling  in  the X and Y dimensions to the final image size.  The routines vpWindow and vpWindowPHIGS are
       useful for computing projection transformations.

STATE VARIABLES

       The current transformation matrix code can be retrieved with the  following  state  variable  codes  (see
       vpGeti(3)): VP_CURRENT_MATRIX.

ERRORS

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

       VPERROR_BAD_OPTION
              The option argument is invalid.

SEE ALSO

       VolPack(3), vpCreateContext(3), vpGetMatrix(3)

VolPack                                                                                       vpCurrentMatrix(3)