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#include <extrusion.h>
Inherits Node.
Inheritance diagram for Extrusion:
Public Member Functions | |
Extrusion (const char *name="") | |
virtual | ~Extrusion () |
virtual unsigned int | nbFields () const |
virtual FieldHandle | field (const std::string &n) |
virtual FieldHandle | field (const unsigned int i) |
virtual bool | isSetToDefaultValue (const unsigned int i) const |
virtual unsigned int | nbEventsIn () const |
virtual EventInHandle | eventIn (const std::string &n) |
virtual EventInHandle | eventIn (const unsigned int i) |
virtual unsigned int | nbEventsOut () const |
virtual EventOutHandle | eventOut (const std::string &n) |
virtual EventOutHandle | eventOut (const unsigned int i) |
const char * | typeName () const |
virtual Node * | duplicate () const |
virtual Node * | duplicate (std::map< const Node *, Node * > &) const |
Public Attributes | |
Fields | |
A property or attribute of a node. Each node type has a fixed set of fields. Fields may contain various kinds of data and one or many values. Each field has a default value. | |
SFBool | beginCap |
SFBool | ccw |
SFBool | convex |
SFFloat | creaseAngle |
MFVec2f | crossSection |
SFBool | endCap |
MFRotation | orientation |
MFVec2f | scale |
SFBool | solid |
MFVec3f | spine |
Events In | |
EventIn< MFVec2f > | set_crossSection |
EventIn< MFRotation > | set_orientation |
EventIn< MFVec2f > | set_scale |
EventIn< MFVec3f > | set_spine |
The Extrusion node specifies geometric shapes based on a two dimensional cross-section extruded along a three dimensional spine in the local coordinate system. The cross-section can be scaled and rotated at each spine point to produce a wide variety of shapes.
An Extrusion node is defined by:
Shapes are constructed as follows. The cross-section curve, which starts as a curve in the Y=0 plane, is first scaled about the origin by the first scale parameter (first value scales in X, second value scales in Z). It is then translated by the first spine point and oriented using the first orientation parameter (as explained later). The same procedure is followed to place a cross-section at the second spine point, using the second scale and orientation values. Corresponding vertices of the first and second cross-sections are then connected, forming a quadrilateral polygon between each pair of vertices. This same procedure is then repeated for the rest of the spine points, resulting in a surface extrusion along the spine.
The final orientation of each cross-section is computed by first orienting it relative to the spine segments on either side of point at which the cross-section is placed. This is known as the spine-aligned cross-section plane (SCP), and is designed to provide a smooth transition from one spine segment to the next (see Figure 6.6). The SCP is then rotated by the corresponding orientation value. This rotation is performed relative to the SCP. For example, to impart twist in the cross-section, a rotation about the Y-axis (0 1 0) would be used. Other orientations are valid and rotate the cross-section out of the SCP.
The SCP is computed by first computing its Y-axis and Z-axis, then taking the cross product of these to determine the X-axis. These three axes are then used to determine the rotation value needed to rotate the Y=0 plane to the SCP. This results in a plane that is the approximate tangent of the spine at each point, as shown in Figure 6.6. First the Y-axis is determined, as follows:
Let n be the number of spines and let i be the index variable satisfying 0 <= i < n:
The Z-axis is determined as follows:
Z = (spine[i+1] - spine[i]) × (spine[i-1] - spine[i])
Z = (spine[1] - spine[0]) × (spine[n-2] - spine[0])
Once the Y- and Z-axes have been computed, the X-axis can be calculated as their cross-product.
If the number of scale or orientation values is greater than the number of spine points, the excess values are ignored. If they contain one value, it is applied at all spine points. The results are undefined if the number of scale or orientation values is greater than one but less than the number of spine points. The scale values shall be positive.
If the three points used in computing the Z-axis are collinear, the cross-product is zero so the value from the previous point is used instead.
If the Z-axis of the first point is undefined (because the spine is not closed and the first two spine segments are collinear) then the Z-axis for the first spine point with a defined Z-axis is used.
If the entire spine is collinear, the SCP is computed by finding the rotation of a vector along the positive Y-axis (v1) to the vector formed by the spine points (v2). The Y=0 plane is then rotated by this value.
If two points are coincident, they both have the same SCP. If each point has a different orientation value, then the surface is constructed by connecting edges of the cross-sections as normal. This is useful in creating revolved surfaces.
Note: combining coincident and non-coincident spine segments, as well as other combinations, can lead to interpenetrating surfaces which the extrusion algorithm makes no attempt to avoid.
The following common cases are among the effects which are supported by the Extrusion node:
Extrusion has three parts: the sides, the beginCap (the surface at the initial end of the spine) and the endCap (the surface at the final end of the spine). The caps have an associated SFBool field that indicates whether each exists (TRUE) or doesn't exist (FALSE).
When the beginCap or endCap fields are specified as TRUE, planar cap surfaces will be generated regardless of whether the crossSection is a closed curve. If crossSection is not a closed curve, the caps are generated by adding a final point to crossSection that is equal to the initial point. An open surface can still have a cap, resulting (for a simple case) in a shape analogous to a soda can sliced in half vertically. These surfaces are generated even if spine is also a closed curve. If a field value is FALSE, the corresponding cap is not generated.
Texture coordinates are automatically generated by Extrusion nodes. Textures are mapped so that the coordinates range in the U direction from 0 to 1 along the crossSection curve (with 0 corresponding to the first point in crossSection and 1 to the last) and in the V direction from 0 to 1 along the spine curve (with 0 corresponding to the first listed spine point and 1 to the last). If either the endCap or beginCap exists, the crossSection curve is uniformly scaled and translated so that the larger dimension of the cross-section (X or Z) produces texture coordinates that range from 0.0 to 1.0. The beginCap and endCap textures' S and T directions correspond to the X and Z directions in which the crossSection coordinates are defined.
The browser shall automatically generate normals for the Extrusion node,using the creaseAngle field to determine if and how normals are smoothed across the surface. Normals for the caps are generated along the Y-axis of the SCP, with the ordering determined by viewing the cross-section from above (looking along the negative Y-axis of the SCP). By default, a beginCap with a counterclockwise ordering shall have a normal along the negative Y-axis. An endCap with a counterclockwise ordering shall have a normal along the positive Y-axis.
Each quadrilateral making up the sides of the extrusion are ordered from the bottom cross-section (the one at the earlier spine point) to the top. So, one quadrilateral has the points:
spine[0](crossSection[0], crossSection[1]) spine[1](crossSection[1], crossSection[0])
in that order. By default, normals for the sides are generated as described in 4.6.3, Shapes and geometry.
For instance, a circular crossSection with counter-clockwise ordering and the default spine form a cylinder. With solid TRUE and ccw TRUE, the cylinder is visible from the outside. Changing ccw to FALSE makes it visible from the inside.
The ccw, solid, convex, and creaseAngle fields are described in 4.6.3, Shapes and geometry.
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Construct a node with all its fields set to default value, which is equivalent to the code below: beginCap = true; ccw = true; convex = true; creaseAngle = 0; crossSection.push_back(SFVec2f(1,1)); crossSection.push_back(SFVec2f(1,-1)); crossSection.push_back(SFVec2f(-1,-1)); crossSection.push_back(SFVec2f(-1,1)); crossSection.push_back(SFVec2f(1,1)); endCap = true; orientation.push_back(SFRotation(0,0,1,0)); scale.push_back(SFVec2f(1,1)); solid = true; spine.push_back(SFVec3f(0,0,0)); spine.push_back(SFVec3f(0,1,0)); |
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Virtual destructor, does nothing |
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Implements Node. |
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Returns a deep copy of this node, that is a fully independant node with all children (if any) also copied. This is mainly useful for instanciating protos. Implements Node. |
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Return a handle on the
This function is useful, with nbEventsIn() if you want to traverse all events in of a Node. Implements Node. |
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Return a handle on the event in named
Implements Node. |
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Return a handle on the Implements Node. |
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Return a handle on the event out named Implements Node. |
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Return a handle on the
Implements Node. |
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Return a handle on the field named
Implements Node. |
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Implements Node. |
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Returns the number of events in for this node type. Implements Node. |
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Returns the number of events out for this node type. Implements Node. |
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Returns the number of fields (exposed or not) for this node type. Implements Node. |
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Returns Implements Node. |
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See Detailed Description for meaning of this field. Default value is set to beginCap = true; |
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See Detailed Description for meaning of this field. Default value is set to ccw = true; |
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See Detailed Description for meaning of this field. Default value is set to convex = true; |
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See Detailed Description for meaning of this field. Default value is set to creaseAngle = 0; |
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See Detailed Description for meaning of this field. Default value is set to crossSection.push_back(SFVec2f(1,1)); crossSection.push_back(SFVec2f(1,-1)); crossSection.push_back(SFVec2f(-1,-1)); crossSection.push_back(SFVec2f(-1,1)); crossSection.push_back(SFVec2f(1,1)); |
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See Detailed Description for meaning of this field. Default value is set to endCap = true; |
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See Detailed Description for meaning of this field. Default value is set to orientation.push_back(SFRotation(0,0,1,0)); |
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See Detailed Description for meaning of this field. Default value is set to scale.push_back(SFVec2f(1,1)); |
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See Detailed Description for meaning of this event. |
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See Detailed Description for meaning of this event. |
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See Detailed Description for meaning of this event. |
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See Detailed Description for meaning of this event. |
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See Detailed Description for meaning of this field. Default value is set to solid = true; |
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See Detailed Description for meaning of this field. Default value is set to |
Generated on 24 Feb 2005 with version 1.3.9.1. |