PEXOCCSetSurfaceApprox - Set Surface Approximation Method (5.0)

Synopsis 

 
   void PEXOCCSetSurfaceApprox(
        PEXOCC context,
        int method,
        double utolerance,
        double vtolerance
   )
 


 
   void PEXSetSurfaceApprox(
        Display *display,
        XID resource_id,
        PEXOCRequestType req_type,
        int method,
        double utolerance,
        double vtolerance
   )

Arguments

context
An OC context returned by a successful PEXCreateOCC call.

display (OCC)
A pointer to a display structure returned by a successful XOpenDisplay call.

resource_id (OCC)
The resource identifier of the renderer or structure.

req_type (OCC)
The request type for the output command (PEXOCRender, PEXOCStore, PEXOCRenderSingle or PEXOCStoreSingle).

method
The surface approximation method (PEXApproxImpDep, PEXApproxConstantBetweenKnots, PEXApproxWCChordalSize, PEXApproxNPCChordalSize, PEXApproxDCChordalSize, PEXApproxWCPlanarDev, PEXApproxNPCPlanarDev, PEXApproxDCPlanarDev, PEXApproxWCRelative, PEXApproxNPCRelative or PEXApproxDCRelative).

utolerance
The surface approximation tolerance in the u direction.

vtolerance
The surface approximation tolerance in the v direction.

Returns

None.

Description

Invoke PEXOCCSetSurfaceApprox to create an attribute output command which sets the surface approximation method attribute in the renderer's pipeline state according to the value specified by method.

By setting the surface approximation attribute's ASF to PEXIndividual (see PEXOCCSetIndividualASF), you use the pipeline state's surface approximation entry to specify the smoothing method to be used when rendering curved bivariate primitives. When you set the surface approximation attribute's ASF to PEXBundled, the implementation uses the surface approximation from the interior bundle table.

PEXlib defines the following surface approximation methods and the use of utolerance and vtolerance:

PEXApproxImpDep -
smooths the surface in an implementation-dependent way and ignores the utolerance and vtolerance. (5.0)

PEXApproxConstantBetweenKnots -
tessellates the surface with equal parametric increments between successive pairs of knots. (5.0)

utolerance and vtolerance controls the tessellation in each of the two parameter dimensions. If you specify a fraction for utolerance or vtolerance, then the implementation truncates it and only uses the integer portion. If you specify a utolerance or vtolerance that is less than or equal to zero, then the surface is evaluated only at the parameter limits and at the knots that are within the specified parameter range in that tolerance's direction. If utolerance or vtolerance is greater than zero, in the tolerance's direction, then the surface is evaluated at the parameter limits, at the knots that are within the specified parameter range, and at the number of positions specified by tolerance between each pair of knots.

PEXApproxWCChordalSize -
tessellates the surface whereby the WC length of each segment (chord) in the u direction is less than the utolerance (specified in world coordinates) and each segment in the v direction is less than the vtolerance (specified in world coordinates). (5.0)

PEXApproxNPCChordalSize -
tessellates the surface whereby the NPC length of each segment (chord) in the u direction is less than the utolerance (specified in normalized projection coordinates) and each segment in the v direction is less than the vtolerance (specified in normalized projection coordinates). (5.0)

PEXApproxDCChordalSize -
tessellates the surface whereby the DC length of each segment (chord) in the u direction is less than the utolerance (specified in device coordinates) and each segment in the v direction is less than the vtolerance (specified in device coordinates). (5.0)

PEXApproxWCChordalDev -
tessellates the surface whereby the deviation in WC's between the surface and its tessellated representation in the u direction does not exceed the utolerance (specified in world coordinates) and the tessellated representation in the v direction does not exceed the vtolerance (specified in world coordinates). (5.0)

PEXApproxNPCChordalDev -
tessellates the surface whereby the deviation in NPC's between the surface and its tessellated representation in the u direction does not exceed the utolerance (specified in normalized projection coordinates) and the tessellated representation in the v direction does not exceed the vtolerance (specified in normalized projection coordinates). (5.0)

PEXApproxDCChordalDev -
tessellates the surface whereby the deviation in DC's between the surface and its tessellated representation in the u direction does not exceed the utolerance (specified in device coordinates) and the tessellated representation in the v direction does not exceed the vtolerance (specified in device coordinates). (5.0)

PEXApproxWCRelative -
indicates, with a utolerance value in the range [0.0, 1.0], a relative quality of rendering to be maintained independent of scaling in world coordinates (WCs). Specify a utolerance of 1.0 for the highest possible quality. The implementation ignores the vtolerance. (5.0)

PEXApproxNPCRelative -
indicates, with a utolerance value in the range [0.0, 1.0], a relative quality of rendering to be maintained independent of scaling in normalized projection coordinates (NPC's). Specify a utolerance of 1.0 for the highest possible quality. The implementation ignores the vtolerance. (5.0)

PEXApproxDCRelative -
indicates, with a utolerance value in the range [0.0, 1.0], a relative quality of rendering to be maintained independent of scaling in device coordinates (DC's). Specify a utolerance of 1.0 for the highest possible quality. The implementation ignores the vtolerance. (5.0)

If the implementation does not support the specified surface approximation method, then the method defaults to PEXApproxImpDep. Inquire the supported values for the surface approximation method by invoking the PEXGetEnumTypeInfo function.

Specify the utolerance and vtolerance to indicate the desired accuracy of the approximation. The surface approximation tolerance has different results depending on which method you specify. See Pipeline Contexts for more information about tolerance values.

This function is a member of the curved surface attribute set.

Errors

BadPEXRenderer
The specified renderer resource identifier is invalid.

BadPEXStructure
The specified structure resource identifier is invalid.

See Also

For an overview and for a list of all output attribute functions, see Output Attribute Functions.