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 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 SoShadowStyle).

This class defines two shadowing methods which can be selected with the method field:

• SHADOW_MAP: In this mode, shadows are not filtered and will display aliasing. Futhermore, it is not compatbile with VolumeViz nodes. All directional lights and spotlights (but not point lights) above this group node are used for computing the shadows. Adding lights as children of this group node will give incorrect results (lights must be defined above this node). Even when using the best quality setting (see quality), some aliasing artifacts will appear if you zoom in very close to the scene. Another way to increase the shadowing quality (decrease the aliasing effects), is to specify a spherical region centered at the camera position within which the shadowing will be computed (see visibilityRadius). The smaller the radius of this sphere, the better the shadow quality. This parameter is particularly useful for walk-through scenes.

VARIANCE_SHADOW_MAP : This mode allows to display soft shadows. The smoothFactor field can be used to increase or decrease the softness. Contrary to the SHADOW_MAP method, aliasing won't be displayed but on large scene, shadows will progressively fade away. Increasing 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 (SoShaderProgram or 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_FragData[0]. 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_FragData[0].xyz = fragColor.xyz * OivComputeShadow();
   gl_FragData[0].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:

• ADD, BLEND: 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).

• ALL SORTED, ALL DELAYED, and SCREEN_DOOR: Same as previous case for VARIANCE_SHADOW_MAP. For SHADOW_MAP method transparent objects neither cast a shadow nor are shadowed.

• SORTED_PIXELS_BLEND: This transparency mode is not compatible with SoShadowGroup. No shadows are computed.

Texture units: In SHADOW_MAP mode this node reserves texture units FXVIZ_SHADOW_TEXTURE_UNIT0 and FXVIZ_SHADOW_TEXTURE_UNIT1 for its rendering (see SoPreferences to set these). If these values are not set, texture units 1 and 2 are used. These values cannot be greater than 3.

In VARIANCE_SHADOW_MAP mode, this node reserves texture unit FXVIZ_SHADOW_TEXTURE_UNIT0 for its rendering (see 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 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 SoFragmentShader.getMaxTextureImageUnit()-SoShaderProgram.getNumReservedTextures(). Note: The value returned by SoShaderProgram.getNumReservedTextures() may change between OpenInventor versions. The total number of available texture units depends on the graphics hardware.

Hardware requirements: NOTE: In SHADOW_MAP mode, at least the Multi-Texture and Texture Environment Combine OpenGL extensions must be supported by your graphics board. Otherwise no shadows will be computed. These extensions are now standard in OpenGL 1.3 and later. 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 isSupported() static method to determine if the current graphics board supports shadowing.

Notes:

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

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

Potential problems: In SHADOW_MAP mode, performance issues and incorrect images have been observed with some OpenGL drivers due to the Texture Border Clamp OpenGL extension (standard in OpenGL 1.3), Try setting the OIV_TEXTURE_BORDER_CLAMP_ENABLE environment variable to 0 in this case. With some graphics boards, especially older hardware like GeForce2, it may be necessary to also set the OIV_FORCE_DUAL_TEX_SHADOW environment variable to 1.

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	SHADOW_MAP
lightBleedingReduction	0.01

}

Reference