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 \fBSoShapeHints::VertexOrdering\fP

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 \fBSoShapeHints::ShapeType\fP

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 \fBSoShapeHints::FaceType\fP

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 ()\fC [protected]\fP, \fC [virtual]\fP

Destructor.

Member Function Documentation

\fBSoType\fP SoShapeHints::getTypeId (void) const\fC [virtual]\fP

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 \fBSoFieldData\fP * SoShapeHints::getFieldData (void) const\fC [protected]\fP, \fC [virtual]\fP

Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoFieldContainer.