Name

PEVMM3 − Returns a view mapping matrix. 

Operating States: PHOP, ∗, ∗, ∗
PHIGS standard function
 

Syntax

PEVMM3 (VWWNLM, PJVPLM, PJTYPE, PJRX, PJRY, PJRZ, VPLD, BPLD, FPLD,
ERRIND, VWMPMT)

Argument     Data Type        Access    Description
---------------------------------------------------------------------------
VWWNLM(4)    Array of reals   Read      View window limits, in view
                                        reference coordinates (UMIN, UMAX,
                                        VMIN, VMAX)
PJVPLM(4)    Array of reals   Read      Projection viewport limits, in
                                        normalized projection coordinates
                                        (XMIN, XMAX, YMIN, YMAX, ZMIN,
                                        ZMAX)
PJTYPE       Integer          Read      Projection type
PJRX, PJRY,  Real             Read      Projection reference point, in view
PJRZ                                    reference coordinates (x, y, z)
VPLD         Real             Read      View plane distance, in view
                                        reference coordinates
BPLD         Real             Read      Back plane distance, in view
                                        reference coordinates
FPLD         Real             Read      Front plane distance, in view
                                        reference coordinates
ERRIND       Integer          Write     Error indicator
VWMPMT(4,4)  Array of reals   Write     View mapping matrix
---------------------------------------------------------------------------

Constants

Defined Argument    Constant    Description
---------------------------------------------------------------------------
PJTYPE              PPARL       Parallel projection
                    PPERS       Perspective projection
---------------------------------------------------------------------------

Description

PEVMM3 returns a view mapping matrix, which can be passed as input to the PSVWR3 function.  The view mapping matrix in the view representation transforms the PHIGS coordinate system from view reference coordinate points to normalized projection coordinate points. 

To create the view mapping matrix, use the following procedure:
 

•Specify window limits (view window) within view reference coordinate space in the order UMIN, UMAX, VMIN, VMAX. 

The following restrictions apply:

UMIN < UMAX

VMIN < VMAX

The resulting view window is a rectangular region on the view plane with sides parallel to the u- and v-axes. 

The formation of the u- and v-axes in the view reference coordinate system is described in Getting Started with DEC PHIGS. 

•Specify projection viewport limits (view clipping limits) within normalized projection coordinate space in the order XMIN, XMAX, YMIN, YMAX, ZMIN, ZMAX. 

The following restrictions apply:

XMIN < XMAX

YMIN < YMAX

ZMIN <= ZMAX

XMIN, XMAX, YMIN, and YMAX must be in the range [0,1], inclusive. 

ZMIN and ZMAX must be in the range [0,1], inclusive. 

The view clipping limits form a rectangular parallelepiped in normalized projection coordinate space with its edges parallel to the normalized projection coordinate axes.  Although the normalized projection coordinate system conceptually extends beyond [0,1] x [0,1] x [0,1], the view clipping limits are located in the closed unit cube [0,1] x [0,1] x [0,1] in normalized projection coordinate space. 

The view, back, and front planes are parallel to the uv-plane of the view reference coordinate system.  They are specified as n coordinate values in the three plane arguments to this function. 

The front- and back-plane values specify the front and back of the view volume.  Conceptually, the view reference coordinate system is oriented to the view reference point, because the view reference coordinate points result from the view orientation transformation. (See the PEVOM3 function.)  Therefore, the front plane should not be positioned behind the back plane. 

The following restrictions apply to the view, front, and back planes:

•Back-plane distance < front-plane distance

•Back-plane distance = front-plane distance, if ZMIN = ZMAX

•The n coordinate of the projection reference point not equal to view plane distance

•For projection type = PERSPECTIVE,
  the n coordinate of the projection reference point is either > front-plane distance or < back-plane distance

Projection and the coordinate systems are described in Getting Started with DEC PHIGS. 

If the view mapping parameters are consistent and well defined (that is, if they conform to the specified rules and restrictions), a call to this function returns the 4 x 4 view mapping matrix.  Otherwise, a nonzero error indicator is returned. 

See Also

PEVOM3
PQVWF
PQVWR
PSVWI
PSVWR3