Chapter 9. Transformation Subroutines

The transformation subroutines found in this section fall into three general categories: modeling clipping, modeling transformations and workstation transformations.

Modeling Clipping

The four modeling clipping subroutines are:

GPMCI

Set Modeling Clipping Indicator

GPMCV2

Set Modeling Clipping Volume 2

GPMCV3

Set Modeling Clipping Volume 3

GPRMCV

Restore Modeling Clipping Volume

The modeling clipping subroutines create modeling clipping structure elements, which modify the current modeling clipping values that the graPHIGS API applies to primitives during traversal.

Modeling Transformations

The four modeling transformation subroutines are:

GPGLX2

Set Global Tranformation 2

GPGLX3

Set Global Transformation 3

GPMLX2

Set Modeling Transformation 2

GPMLX3

Set Modeling Transformation 3

The modeling transformation subroutines create transformation structure elements, which modify the current transformation values that the graPHIGS API applies to primitives during traversal.

Workstation Transformations

The three workstation transformation subroutines are:

GPDCMM

Set Device Coordinate Mapping Method

GPWSX2

Set Workstation Transformation 2

GPWSX3

Set Workstation Transformation 3

Note:

When the graPHIGS API inserts a structure element into an open structure following the element pointer, the pointer moves to the new element.

GPBDMF - Set Back Data Morphing Factors

Purpose

Use GPBDMF to insert a Set Back Data Morphing Factors structure element into the open structure following the element pointer, or to replace the element pointed at by the element pointer with a Set Back Data Morphing Factors structure element, depending on the current edit mode.

During traversal, the graPHIGS API combines the values of fdata with a primitive's data morphing vectors to modify its rendered data mapping data. If the face distinguish mode (GPFDMO) is 1=NONE , then the graPHIGS API uses the current data morphing scale factors when performing data mapping on the back facing portions of area primitives. If the face distinguish mode is 2=COLOR_SURFACE_PROPERTIES , then the graPHIGS API uses these values when performing data mapping on only back facing portions of area primitives.

In data morphing, the graPHIGS API combines the data mapping data values (x₁ , x₂ , ..., x_ndata ) with the back data morphing scale factors in the fdata parameter (s₁ , s₂ , ..., s_nscale ) and the data morphing vectors ((d_1,1 , d_1,2 , ..., d_1,ndata ),  (d_2,1 , d_2,2 , ..., d_2,ndata ), ...,  (d_nvector,1 , d_nvector,2 , ..., d_{nvector,ndata} )) to obtain the new back data mapping data values (x'₁ , x'₂ , ..., x'_ndata ). This combination is of the form:

x'₁ = s₁ x₁ + s₂ d_1,1 + s₃ d_2,1 +...+ s_nscale d_nvector,1
x'₂ = s₁ x₂ + s₂ d_1,2 + s₃ d_2,2 +...+ s_{nscale nvector,2}
...
x'_ndata = s₁ x_ndata + s₂ d_{1, ndata} + s₃ d₂ ,ndata> +...+ s_nscale d_{nvector,ndata}

These equations show that the number of morphing scale factors should be one more than the number of morphing vectors in the affected primitive (nscale=nvector+1). However, if the number of morphing vectors and scale factors disagree at traversal time, then 0 value vectors and scale factors are assumed wherever necessary. For example, if you supply too many scale factors for a given primitive (nscale>nvector+1), then the graPHIGS API ignores the extra scale factors, as if there were additional 0 valued morphing vectors in the primitive definition. If you supply too few scale factors (nscale<nvector+1), then the graPHIGS API ignores the extra morphing vectors, just as if there were additional scale factors with value zero in this function call.

The traversal default for data morphing is flength=1 and fdata={1.0}

Use GPQWDT to inquire the morphing facilities of a specified workstation.

Parameters