Provided by: libcoin80-doc_3.1.4~abc9f50-4ubuntu2_all 
NAME
SoShapeHints -
The SoShapeHints class is a node containing hints about how to render geometry.
The SoShapeHints node is used to set up clues to the rendering subsystem about how
particular aspects of the subsequent geometry in the scene graph should be drawn.
SYNOPSIS
#include <Inventor/nodes/SoShapeHints.h>
Inherits SoNode.
Public Types
enum VertexOrdering { UNKNOWN_ORDERING = SoShapeHintsElement::UNKNOWN_ORDERING, CLOCKWISE
= SoShapeHintsElement::CLOCKWISE, COUNTERCLOCKWISE =
SoShapeHintsElement::COUNTERCLOCKWISE }
enum ShapeType { UNKNOWN_SHAPE_TYPE = SoShapeHintsElement::UNKNOWN_SHAPE_TYPE, SOLID =
SoShapeHintsElement::SOLID }
enum FaceType { UNKNOWN_FACE_TYPE = SoShapeHintsElement::UNKNOWN_FACE_TYPE, CONVEX =
SoShapeHintsElement::CONVEX }
enum WindingType { NO_WINDING_TYPE = 0 }
Public Member Functions
virtual SoType getTypeId (void) const
Returns the type identification of an object derived from a class inheriting SoBase.
This is used for run-time type checking and 'downward' casting.
SoShapeHints (void)
virtual void doAction (SoAction *action)
virtual void GLRender (SoGLRenderAction *action)
virtual void callback (SoCallbackAction *action)
virtual void getBoundingBox (SoGetBoundingBoxAction *action)
virtual void pick (SoPickAction *action)
Static Public Member Functions
static SoType getClassTypeId (void)
static void initClass (void)
Public Attributes
SoSFEnum vertexOrdering
SoSFEnum shapeType
SoSFEnum faceType
SoSFEnum windingType
SoSFBool useVBO
SoSFFloat creaseAngle
Protected Member Functions
virtual const SoFieldData * getFieldData (void) const
virtual ~SoShapeHints ()
Static Protected Member Functions
static const SoFieldData ** getFieldDataPtr (void)
Additional Inherited Members
Detailed Description
The SoShapeHints class is a node containing hints about how to render geometry.
The SoShapeHints node is used to set up clues to the rendering subsystem about how
particular aspects of the subsequent geometry in the scene graph should be drawn.
Here is an example on how to display a scene in wireframe mode which only shows the
triangles facing towards the camera.
#include <Inventor/nodes/SoCone.h>
#include <Inventor/nodes/SoDrawStyle.h>
#include <Inventor/nodes/SoLightModel.h>
#include <Inventor/nodes/SoSeparator.h>
#include <Inventor/nodes/SoShapeHints.h>
#include <Inventor/Win/SoWin.h>
#include <Inventor/Win/viewers/SoWinExaminerViewer.h>
int main(int, char * argv[])
{
HWND window = SoWin::init(argv[0]);
SoSeparator * root = new SoSeparator;
// wireframe
SoDrawStyle * drawStyle = new SoDrawStyle;
drawStyle->style = SoDrawStyle::LINES;
root->addChild(drawStyle);
// back-face culling
SoShapeHints * shapeHints = new SoShapeHints;
shapeHints->vertexOrdering = SoShapeHints::COUNTERCLOCKWISE;
shapeHints->shapeType = SoShapeHints::SOLID;
root->addChild(shapeHints);
// keep a solid color
SoLightModel * lightModel = new SoLightModel;
lightModel->model = SoLightModel::BASE_COLOR;
root->addChild(lightModel);
// a cone
SoCone * cone = new SoCone;
root->addChild(cone);
// set up a window
SoWinExaminerViewer * viewer = new SoWinExaminerViewer(window);
SbViewportRegion vpRegion = viewer->getViewportRegion();
viewer->setSceneGraph(root);
viewer->show();
SoWin::mainLoop();
delete viewer;
return 0;
}
The default settings of the rendering system is tuned towards programmer convenience. For
instance, the default is to render both sides of all polygons to make sure we avoid any
'holes' in the geometry if the vertex ordering should happen to differ for different
polygons.
If the programmer gives up some of this convenience and uses SoShapeHints nodes to more
closely specify information about the scene graph geometry, the clues given by the
SoShapeHints node(s) will then be used by the rendering subsystem to avoid certain costly
operations. Significant gains in rendering speed could be seen as a result.
Be aware that the way backface culling and two-sided lighting is decided by the rendering
system is not at all intuitive. Here are the common rules of how primitive shapes will
render themselves with regard to how the SoShapeHints::vertexOrdering and
SoShapeHints::shapeType fields are set:
• vertexOrdering == CLOCKWISE or COUNTERCLOCKWISE, shapeType == SOLID: causes primitives
to be backface culled and rendered with one-sided lighting.
• vertexOrdering == CLOCKWISE or COUNTERCLOCKWISE, shapeType == UNKNOWN_SHAPE_TYPE:
primitives are not backface culled, and they are rendered with two-sided lighting.
• vertexOrdering == UNKNOWN_ORDERING, any shapeType: primitives are not backface culled,
and they are rendered with one-sided lighting. The OpenGL vertex ordering will be set to
counter clockwise ordering.
The UNKNOWN_ORDERING enum has a special and non-intuitive meaning. The ordering is really
set to counter clockwise -- in OpenGL and when generating normals. However, if you want to
render your geometry with one-sided lighting and backface culling disabled, you have to
use this enum value, and your polygons need to be in counter clockwise ordering.
FILE FORMAT/DEFAULTS:
ShapeHints {
vertexOrdering UNKNOWN_ORDERING
shapeType UNKNOWN_SHAPE_TYPE
faceType CONVEX
creaseAngle 0
}
Member Enumeration Documentation
enum SoShapeHints::VertexOrdering
Enumeration of available ways to specify ordering of vertices for a polygon.
Enumerator
UNKNOWN_ORDERING
Ordering not known, render both sides of the polygon.
CLOCKWISE
Vertices are specified in a clockwise order.
COUNTERCLOCKWISE
Vertices are specified in a counter-clockwise order.
enum SoShapeHints::ShapeType
Enumeration of different shape types.
Enumerator
UNKNOWN_SHAPE_TYPE
Nothing known about the shape, be conservative when rendering.
SOLID The subsequent shapes in the graph are all known to be completely 'closed', solid
3D shapes. Backface culling will be done if vertexOrdering is known.
enum SoShapeHints::FaceType
Enumeration of polygon face types.
Enumerator
UNKNOWN_FACE_TYPE
Signifies: nothing is known about subsequent polygon data, be conservative when
rendering.
All polygons in the scene will be analyzed to see if they needs to be tessellated (broken
up) into triangles before passed on to the underlying immediate mode rendering system.
The OpenGL rendering system handles most complex polygon types, but not all: it can for
instance have problems with many-sided, concave polygons (concave polygons are 'hollow',
that is: rounded inwards). Coin's internal tessellator will most often handle the cases
that OpenGL fails on.
So if you are seeing weird artifacts in how complex polygons are rendered, try to change
the SoShapeHints::faceType field to this value and see if they are then rendered
correctly.
Beware that turning on this functionality might have the effect of making the rendering
performance worse. If it has a noticable effect on your particular scenegraph, we advise
that you investigate whether you could change how the polygons are generated for Coin
rendering and then avoid using this flag.
CONVEX Subsequent faces are all convex, so turn off the check for and tessellation of
inconvex faces.
Subsequent polygons from faceset-type nodes (like SoFaceSet and SoIndexedFaceSet) will be
sent unmodified to OpenGL, thereby assuming that the polygons are in a form handled by
OpenGL.
Constructor & Destructor Documentation
SoShapeHints::SoShapeHints (void)
Constructor.
SoShapeHints::~SoShapeHints () [protected], [virtual]
Destructor.
Member Function Documentation
SoType SoShapeHints::getTypeId (void) const [virtual]
Returns the type identification of an object derived from a class inheriting SoBase. This
is used for run-time type checking and 'downward' casting. Usage example:
void foo(SoNode * node)
{
if (node->getTypeId() == SoFile::getClassTypeId()) {
SoFile * filenode = (SoFile *)node; // safe downward cast, knows the type
}
}
For application programmers wanting to extend the library with new nodes, engines,
nodekits, draggers or others: this method needs to be overridden in all subclasses. This
is typically done as part of setting up the full type system for extension classes, which
is usually accomplished by using the pre-defined macros available through for instance
Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes),
Inventor/engines/SoSubEngine.h (for engine classes) and so on.
For more information on writing Coin extensions, see the class documentation of the
toplevel superclasses for the various class groups.
Implements SoBase.
const SoFieldData * SoShapeHints::getFieldData (void) const [protected], [virtual]
Returns a pointer to the class-wide field data storage object for this instance. If no
fields are present, returns NULL.
Reimplemented from SoFieldContainer.
void SoShapeHints::doAction (SoAction *action) [virtual]
This function performs the typical operation of a node for any action.
Reimplemented from SoNode.
void SoShapeHints::GLRender (SoGLRenderAction *action) [virtual]
Action method for the SoGLRenderAction.
This is called during rendering traversals. Nodes influencing the rendering state in any
way or who wants to throw geometry primitives at OpenGL overrides this method.
Reimplemented from SoNode.
void SoShapeHints::callback (SoCallbackAction *action) [virtual]
Action method for SoCallbackAction.
Simply updates the state according to how the node behaves for the render action, so the
application programmer can use the SoCallbackAction for extracting information about the
scene graph.
Reimplemented from SoNode.
void SoShapeHints::getBoundingBox (SoGetBoundingBoxAction *action) [virtual]
Action method for the SoGetBoundingBoxAction.
Calculates bounding box and center coordinates for node and modifies the values of the
action to encompass the bounding box for this node and to shift the center point for the
scene more towards the one for this node.
Nodes influencing how geometry nodes calculates their bounding box also overrides this
method to change the relevant state variables.
Reimplemented from SoNode.
void SoShapeHints::pick (SoPickAction *action) [virtual]
Action method for SoPickAction.
Does common processing for SoPickAction action instances.
Reimplemented from SoNode.
Member Data Documentation
SoSFEnum SoShapeHints::vertexOrdering
Specifies how vertices are ordered for polygon faces.
Set this field to SoShapeHints::CLOCKWISE or SoShapeHints::COUNTERCLOCKWISE if possible to
turn on backface culling and thereby optimize rendering.
Default value is SoShapeHints::UNKNOWN_ORDERING.
SoSFEnum SoShapeHints::shapeType
Hint about whether or not shapes are known to be 'closed'. Default value is
SoShapeHints::UNKNOWN_SHAPE_TYPE.
SoSFEnum SoShapeHints::faceType
Hint about whether or not polygon faces are known to be convex. Default value is
SoShapeHints::CONVEX.
SoSFFloat SoShapeHints::creaseAngle
When normals are automatically generated by Coin (i.e. SoNormal nodes are not used), this
is the smallest angle between two faces where we would still calculate normals to do
flatshading.
If the angle between the normals of two neighboring faces is less than the value of this
field, the faces will be smoothshaded around their common edge.
The angle is specified in radians, and the default value is 0.0, meaning no smoothing will
be done by default.
Author
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