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Rendering Functions |
Rendering Functions
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Parasolid provides two rendering functions at the PK interface level:
It is passed an options structure PK_GEOM_render_line_o_t which is initialized to a default state by PK_GEOM_render_line_o_m. The application can then reset option fields to specific values.
Applications should initialize the PK_GEOM_render_line_o_t structure in this way, rather than trying to set all of the fields individually. The
o_t_version
value which is initialized by PK_GEOM_render_line_o_m must not be modified.
This function supports the rendering styles:
It is passed an option structure PK_TOPOL_render_line_o_t which is initialized to a default state by PK_TOPOL_render_line_o_m. The application can then reset option fields to specific values.
Applications should initialize the PK_TOPOL_render_line_o_t structure in this way and should not modify the value of the
o_t_version
field.
The two rendering functions enable you to produce wire frame and hidden line pictures (through the GO) of your models (parts). Pictures consist of the following types of line:
The following diagram shows each kind of line, except hatch lines which are detailed later.
The blend on the near edge of this block is in fact unfixed. If the blend had been created using the
draw_fix
blending option then by default, the blend boundary and ribs would not have been drawn, and the unblended edge would.
For further information on the
draw_fix
blending option see the documentation under "Draw, check, fix" in Chapter 30, "Edge Blending Functions and Options".
PK_GEOM_render_line generates a 3-D representation of bounded curves and surfaces, foreign geometry curves and surfaces and their derived offset surfaces.
It allows an application to draw an approximate representation of one or more geometric entities in a "wire mesh" form.
Options control the generation of surface boundary, hatch line data and the output format of B-curve data.
PK_GEOM_render_line_o_m initializes the options:
These defaults can be overwritten as required.
Geometric entities can be rendered in local coordinates or be subject to selective transformation, using the
geom_transfs
argument.
PK_TOPOL_render_line generates a 3-D representation of parts, faces and edges.
Topological entities can be rendered in local coordinates or be subject to selective transformation, using the
topol_transfs
argument.
To generate a basic "wire frame" drawing, PK_TOPOL_render_line is called with the options:
PK_TOPOL_render_line_o_m initializes the option structure to select the above options, also setting the options:
These defaults can be overwritten as required.
The basic "wire frame" drawing described above does not include any view dependent data. For example, rendering a hemispherical body draws the base circle but provides no visual cues about the spherical face.
To generate additional view dependent data, PK_TOPOL_render_line should be called with the option:
and specify the current view using a PK_TRANSF_t entity.
The application must apply a copy of the view matrix underlying the PK transform entity to all graphics output data to convert it from GO's world coordinate system to the application's view coordinate system before display.
To generate a hidden line drawing, PK_TOPOL_render_line is called with the options:
The application passes its current view to PK_TOPOL_render_line using a PK transform entity, in the same way as when rendering view dependent topology.
The
visibility
option generates additional data which allow hidden portions of lines to be suppressed entirely or be output with a code classifying them as invisible.
The default
visibility
setting of 'no visibility' is used when rendering view independent or view dependent topology (wire-frame drawings).
Figure 52-2 Hidden line output of an edge, edge X, that is partially visible
Hidden line drawing also requires a specification of the current view, using a PK transform entity. The application must apply a copy of the underlying view matrix to all graphics output data in the same way as described for "View dependent topology". Silhouettes and transitions from visible to invisible only look right in the view specified by the view matrix.
Geometric entities (such as bounded curves and surfaces) are drawn using PK_GEOM_render_line.
Topological entities (parts or collections of faces and edges) are drawn using PK_TOPOL_render_line.
If an array of entities is passed to either of these functions it must not contain duplicates, unless an array of transformation entities is also supplied, implying that occurrences of entities are non-coincident.
Each entity in the array of geometric or topological entities is identified by an occurrence number.
This occurrence number is passed onto GO and output as the first element of the
lntp
array in calls to GOOPSG, GOSGMT and GOCLSG. The value is equal to the array index of the originating entity, plus 1, i.e. GO occurrence numbers are output starting at 1. When faces or edges appear in the array of topological entities, a call to GOOPSG is made for the owning body with an occurrence number of zero.
Occurrence numbers allow you to associate entity occurrences with a particular sequences of calls to GO functions arising within a single call to one of the rendering functions. This is useful, for example, when you are outputting faces on an interleaved, rather than body by body, basis, and need to keep track of which face is associated with which body. See "go_interleaved" in Chapter 55, "Faceting Output Via GO", for more information on outputting interleaved data.
The PK rendering functions can be passed an array of transformation entities, allowing selective transformation of individual geometric or topological entities.
In PK_GEOM_render_line, this allows curve and surface geometry to be overlaid onto a drawing produced by PK_TOPOL_render_line.
In PK_TOPOL_render_line, this allows generation of the following types of line drawing in wireframe or hidden line form:
An array entry of PK_ENTITY_null denotes that a particular entity should not be transformed.
A NULL address implies that no entities should be transformed.
A viewing transformation is needed when PK_TOPOL_render_line is used to generate silhouette and hidden line data. This is explained in Chapter 49, "Parasolid View Matrices".
PK_GEOM_render_line and PK_TOPOL_render_line allow tolerances to be specified, to be used when rendering curves in a part. These approximation tolerances control the accuracy of the polyline representation of the curves.
These tolerances are explained in Chapter 50, "Display Tolerances".
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