SoShapeHints Class Reference
[Node Classes]

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. More...

#include <Inventor/nodes/SoShapeHints.h>

Inheritance diagram for SoShapeHints:

List of all members.

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
	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 void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.
Public Attributes
SoSFEnum	vertexOrdering
SoSFEnum	shapeType
SoSFEnum	faceType
SoSFEnum	windingType
SoSFBool	useVBO
SoSFFloat	creaseAngle
Protected Member Functions
virtual	~SoShapeHints ()

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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
    }

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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.

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Constructor & Destructor Documentation

SoShapeHints::SoShapeHints

(

void

)

Constructor.

SoShapeHints::~SoShapeHints

(

)

[protected, virtual]

Destructor.

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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.

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The documentation for this class was generated from the following files:

• SoShapeHints.h
• SoShapeHints.cpp