This group node performs real-time shadow casting. Because shadows depends on a lot of OpenInventor elements, it is recommended to put children of this group under a OIV.Inventor.Nodes.SoSeparator in order to have a cache. Each shape within this group will be included in the shadow casting computation. A shape may cast a shadow on other shapes or on itself (self-shadowing), and/or may be shadowed by other shapes within the group. The current shadow style is used to determine if shapes cast a shadow and/or can be shadowed (see OIV.Inventor.Nodes.SoShadowStyle).

This class defines a single shadowing method. The OIV.Inventor.Nodes.SoShadowGroup.method field allows for future shadowing methods to be added.

• VARIANCE_SHADOW_MAP : This mode allows to display soft shadows. The OIV.Inventor.Nodes.SoShadowGroup.smoothFactor field can be used to increase or decrease the softness. Aliasing won't be displayed, but on large scenes shadows will progressively fade away. Increasing OIV.Inventor.Nodes.SoShadowGroup.quality will reduce this problem. Only the last on state directional light is used during rendering, other lights are ignored.

  Shaders Only the VARIANCE_SHADOW_MAP method is available with shaders (custom or internal). In order to use shadows with user defined GLSL shaders (OIV.Inventor.Nodes.SoShaderProgram or OIV.VolumeViz.Nodes.SoVolumeShader), the following functions must be used in the shader programs. In the vertex shader:

  • void OivSetupShadowVertex(): Must be called in the vertex shader.

  In the fragment shader:

  • float OivComputeShadow(): Returns a scalar in [0-1]. 0 means fragment is fully shadowed, 1 means no shadow. Should be used to modify the fragment color.

  • void OivGenerateShadowMap(): Must be called during the shadowmap pass in order to create the shadowmap. During this pass, the shader must not write to gl_FragColor. Use the uniform OivShadowPass to know when the shadowmap is being computed.

  The following uniform is available in vertex and fragment shaders:

  • uniform bool OivShadowPass: Is true if the shadowmap is currently being rendered

  The following code can be used as a skeleton for a GLSL shader that works with shadows:

  Copy

  void OivSetupShadowVertex();
  void main()
  {
   ..userCode..
   //Needed for shadowing
   OivSetupShadowVertex();
  }
  
  uniform bool OivShadowPass;
  
  void OivGenerateShadowMap();
  float OivComputeShadow();
  void main()
  {
   if ( !OivShadowPass ) {
     ..compute fragment color here..
     // Define the final color
     gl_FragColor.xyz = fragColor.xyz * OivComputeShadow();
     gl_FragColor.w = fragColor.w;
   }
   else {
     // Output the shadowmap during the shadow map pass
     OivGenerateShadowMap();
   }
  }

  Transparency: Transparent objects are treated as follows, depending on the transparency type:

  • NO_SORT: Transparent objects cast a shadow and are shadowed but the shadow intensity doesn't depend on the transparency value (the same shadow is displayed for full transparent shapes and opaque shapes).

  • OPAQUE_FIRST, SORTED_OBJECT and SORTED_PIXEL: Same as previous case for VARIANCE_SHADOW_MAP.

  Texture units: In VARIANCE_SHADOW_MAP mode, this node reserves texture unit OIV_SHADOW_TEXTURE_UNIT0 for its rendering (see OIV.Inventor.SoPreferences to set these). If this value is not set the application can specify which texture units OpenInventor should automatically use by setting environment variables (see OIV.Inventor.SoPreferences). The texture units between OIV_FIRST_RESERVED_TEXTURE_UNIT and OIV_FIRST_RESERVED_TEXTURE_UNIT+SoShaderProgram.getNumReservedTextures()-1 inclusive are reserved for internal OpenInventor use. If OIV_FIRST_RESERVED_TEXTURE_UNIT is not set, its default value is OIV.Inventor.Nodes.SoFragmentShader.GetMaxTextureImageUnit()-SoShaderProgram.getNumReservedTextures(). Note: The value returned by OIV.Inventor.Nodes.SoShaderProgram.GetNumReservedTextures() may change between OpenInventor versions. The total number of available texture units depends on the graphics hardware.

  Hardware requirements: The Shadow and Depth Texture OpenGL extensions (standard in OpenGL 1.4) are used if they are available and generally improve performance. In order to increase quality and performance of the shadows, OpenGL PBuffers are used. PBuffers are a limited resource on some systems. Set OIV_PBUFFER_ENABLE to 0 to disallow use of PBuffers.

  A DirectX 10 graphics board is needed to support VARIANCE_SHADOW_MAP.

  Use the OIV.Inventor.Nodes.SoShadowGroup.IsSupported(OIV.Inventor.Nodes.SoShadowGroup.ShadowingMethods) static method to determine if the current graphics board supports shadowing.

  Limitations

  • OIV.Inventor.Nodes.SoShadowGroup cannot be nested by design.

  Notes:

  • Geometry cannot receive shadows if lighting is disabled. For example if an OIV.Inventor.Nodes.SoLightModel node sets the lighting model to BASE_COLOR.

  • Geometry cannot receive shadows if a texture is applied using the DECAL or REPLACE models.

  FILE FORMAT/DEFAULT

  ShadowGroup {

  isActive	true
  isShapesBefore	false
  intensity	0.5
  precision	0.5
  quality	0.5
  shadowCachingEnabled	true
  visibilityRadius	1.0
  visibilityFlag	LONGEST_BBOX_EDGE_FACTOR
  smoothFactor	1
  minVariance	1e-5
  method	VARIANCE_SHADOW_MAP
  lightBleedingReduction	0.01

  }

Reference