SET TRIMMING CURVE APPROXIMATION CRITERIA(3P+) — MISC. REFERENCE MANUAL PAGES

NAME

SET TRIMMING CURVE APPROXIMATION CRITERIA − create a structure element to set the trimming curve approximation criteria

SYNOPSIS

C Syntax

void
psettrimcurvapprox ( type, value )
Pinttype;approximation type
Pfloatvalue;approximation value

FORTRAN Syntax

SUBROUTINE pstapx ( TYPE, VALUE )
INTEGERTYPEapproximation type
REALVALUEapproximation value

Required PHIGS Operating States

(PHOP, ∗, STOP ∗)

DESCRIPTION

Purpose

SET TRIMMING CURVE APPROXIMATION CRITERIA places into the currently open structure a structure element that specifies the trimming curve approximation type and value. The trimming curve approximation type controls the display precision of trimming curves by specifying the method to use to render the trimming curve.

When the current trimming curve approximation criteria Aspect Source Flag (ASF) is set to INDIVIDUAL, the current value of this attribute defines the trimming curve approximation criteria to be applied to the following output primitives:

• NON-UNIFORM B-SPLINE SURFACE

This is a SunPHIGS Extension function and is not part of the PHIGS standard.

C Input Parameters

All of the following data types are predefined in phigs.h.

typeThe curve approximation type. Predefined values are:

0PCURV_WS_DEP
1PCURV_CONSTANT_PARAMETRIC
2PCURV_CONSTANT_PARAMETRIC_BETWEEN_KNOTS

valueThe value to use when applying the specified approximation method. Valid values depend on the approximation method specified. See the Execution section below for a description of the use of value by each approximation method.

FORTRAN Input Parameters

All of the following data types are predefined in phigs77.h.

TYPEThe curve approximation type. Predefined values are:

0PCAWSDWorkstation Dependent
1PCAEPConstant Parametric Subdivision
2PCAEPKConstant Parametric Subdivision Between Knots

VALUE
The value to use when applying the specified approximation method. Valid values depend on the approximation type specified. See the Execution section below for a description of the use of VALUE by each approximation method.

Execution

Depending on the edit mode, a SET TRIMMING CURVE APPROXIMATION CRITERIA element is either inserted into the open structure after the element pointer, or replaces the element pointed at by the element pointer. The element pointer is then updated to point to this SET TRIMMING CURVE APPROXIMATION CRITERIA element.

The approximation methods corresponding to the defined approximation types and the use of the approximation value by each method are:

Workstation Dependent, Type 0
Use a workstation dependent approximation method.

Constant Parametric Subdivision, Type 1
Tessellate using equal parametric increments along the entire trimming curve. The integer portion of the approximation value is used and interpreted as follows:

≤ 0: Evaluate the trimming curve only at the parameter limits.

> 0: Evaluate the trimming curve at the parameter limits and at the specified number of positions between the parameter limits.

Constant Parametric Subdivision Between Knots, Type 2
Tessellate using equal parametric increments between each pair of knots on the trimming curve. The integer portion of the approximation value is used and interpreted as follows:

≤ 0: Evaluate the trimming curve only at the parameter limits and at the knots that fall within the parameter limits.

> 0: Evaluate the trimming curve at the parameter limits, at the knots that fall within the parameter limits, and at the specified number of positions between each pair of knots, but only if the position is within the parameter limits.

At traversal time, approximation type zero (Workstation Dependent) and an approximation value of one are used if the specified approximation type is not supported by the workstation. If the approximation value is inconsistent with the specified approximation type, a value of one will be used. The approximation types supported by a workstation type can be determined with the function INQUIRE CURVE AND SURFACE FACILITIES.

When the current trimming curve approximation criteria ASF is set to INDIVIDUAL, area-defining output primitives which follow in the structure network are filled using the current trimming curve approximation criteria.

When the current trimming curve approximation criteria ASF is set to BUNDLED, the trimming curve approximation criteria is taken from the workstation extended representation indicated by the current interior index. In this case, the trimming curve approximation criteria set with SET TRIMMING CURVE APPROXIMATION CRITERIA has no effect.

ERRORS

005Ignoring function, function requires state (PHOP, ∗, STOP, ∗)

Museum