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. The shadow casting computation takes into account all shapes contained in this group. It ignores shapes in other groups. Depending on the parameters of the lights in the scene, a shape within this group may cast and receive shadows:

• on/from itself (self-shadowing)

• on/from other shapes (also within this group) The current shadow style determines if shapes can cast shadows and/or have shadows cast onto them (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 displays soft shadows. The OIV.Inventor.Nodes.SoShadowGroup.smoothFactor field increases or decreases the softness. It does not display aliasing, but on large scenes shadows will progressively fade away. Increasing OIV.Inventor.Nodes.SoShadowGroup.quality reduces this problem.

Lights

• Shadows are cast by OIV.Inventor.Nodes.SoLight nodes placed before the OIV.Inventor.Nodes.SoShadowGroup node in the scene graph.

• OIV.Inventor.Nodes.SoLight nodes included in the OIV.Inventor.Nodes.SoShadowGroup node do not cast any shadow.

• If there are no OIV.Inventor.Nodes.SoLight nodes before the OIV.Inventor.Nodes.SoShadowGroup node, no shadow is cast.

• The shape of the shadows depend on the parameters of the OIV.Inventor.Nodes.SoLight nodes and on the type of light. Only OIV.Inventor.Nodes.SoDirectionalLight, OIV.Inventor.Nodes.SoPointLight and OIV.Inventor.Nodes.SoQuadAreaLight light types cast shadows.

• OIV.Inventor.Nodes.SoShadowGroup supports shadowing with up to 8 simultaneous lights.

• OIV.Inventor.Nodes.SoLight.shadowIntensity controls the intensity of the shadows cast by that light node. This intensity is multiplied by the value of OIV.Inventor.Nodes.SoShadowGroup.intensity to give the final intensity of that light's shadow.

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:

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 + OIV.Inventor.Nodes.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.

• The shadows cast by an OIV.Inventor.Nodes.SoQuadAreaLight do not take the size of its area into account. An OIV.Inventor.Nodes.SoQuadAreaLight casts the same shadows as an OIV.Inventor.Nodes.SoPointLight positioned at the center of the quadrangle.

• OIV.Inventor.Nodes.SoShadowGroup does not support OIV.Inventor.Nodes.SoSpotLight nodes and they do not cast any shadow.

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