vpCurrentMatrix - choose the current transformation matrix
vpc VolPack context from vpCreateContext.
option A code specifying one of the VolPack transformation matrices
(VP_MODEL, VP_VIEW or VP_PROJECT).
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
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
The current transformation matrix code can be retrieved with the
following state variable codes (see vpGeti(3)): VP_CURRENT_MATRIX.
The normal return value is VP_OK. The following error return value is
The option argument is invalid.
VolPack(3), vpCreateContext(3), vpGetMatrix(3)