SoShadowGroup Class Reference
[Groups]

Shadow casting group node More...

#include <Inventor/nodes/SoShadowGroup.h>

Inheritance diagram for SoShadowGroup:

Public Types
enum	VisibilityFlag { ABSOLUTE_RADIUS, LONGEST_BBOX_EDGE_FACTOR }
enum	ShadowingMethod { VARIANCE_SHADOW_MAP }
Public Member Functions
virtual SoType	getTypeId () const
	SoShadowGroup ()
	SoShadowGroup (int nChildren)
Static Public Member Functions
static SoType	getClassTypeId ()
static SbBool	isSupported (SoShadowGroup::ShadowingMethod method=SoShadowGroup::VARIANCE_SHADOW_MAP)
Public Attributes
SoSFBool	isActive
SoSFFloat	intensity
SoSFFloat	precision
SoSFFloat	quality
SoSFBool	shadowCachingEnabled
SoSFFloat	visibilityRadius
SoSFEnum	visibilityFlag
SoSFInt32	smoothFactor
SoSFFloat	minVariance
SoSFFloat	lightBleedingReduction
SoSFEnum	method

Detailed Description

Shadow casting group node

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 a single shadowing method. The method field allows for future shadowing methods to be added.

VARIANCE_SHADOW_MAP : This mode allows to display soft shadows. The 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 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_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:

 // The vertex shader:
 void OivSetupShadowVertex();
 void main()
 {
   ..userCode..
   //Needed for shadowing
   OivSetupShadowVertex();
 }

 // The fragment shader:
 //If true we are in shadowmap generation pass
 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 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+SoShaderProgramgetNumReservedTextures()-1 inclusive are reserved for internal OpenInventor use. If OIV_FIRST_RESERVED_TEXTURE_UNIT is not set, its default value is SoFragmentShader::getMaxTextureImageUnit()-SoShaderProgramgetNumReservedTextures(). 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:
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.

Limitations

SoShadowGroup cannot be nested by design.

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.

FILE FORMAT/DEFAULT

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

Member Enumeration Documentation

enum SoShadowGroup::ShadowingMethod

Shadowing techniques.

Enumerator:

VARIANCE_SHADOW_MAP

Shadows with soft edges.

enum SoShadowGroup::VisibilityFlag

visibilityRadius interpretation

Enumerator:

ABSOLUTE_RADIUS

visibilityRadius is interpreted as an absolute value.

LONGEST_BBOX_EDGE_FACTOR

The longest edge of the scene bounding box will be multiplied by the value of visibilityRadius.

The resulting value will be the radius within which shadows are computed.

Constructor & Destructor Documentation

SoShadowGroup::SoShadowGroup ( )

Default constructor.

SoShadowGroup::SoShadowGroup ( int nChildren )

Constructor that takes approximate number of children.

Member Function Documentation

static SoType SoShadowGroup::getClassTypeId ( ) [static]

Returns the type identifier for this class.

Reimplemented from SoGroup.

virtual SoType SoShadowGroup::getTypeId ( ) const [virtual]

Returns the type identifier for this specific instance.

Reimplemented from SoGroup.

static SbBool SoShadowGroup::isSupported ( SoShadowGroup::ShadowingMethod method = SoShadowGroup::VARIANCE_SHADOW_MAP ) [static]

Indicates if shadow casting is supported by your graphic board.

When using a debug build of Open Inventor, some "no context available" warning messages may be generated. You can ignore them or see SoGLExtension for an example of using SoGLContext to avoid them.

Member Data Documentation

SoSFFloat SoShadowGroup::intensity

Specifies the intensity of the shadow.

0 = lowest intensity (the shadow is invisible), 1 = highest intensity (the shadow is solid black).

SoSFBool SoShadowGroup::isActive

Activates/deactivates the shadowing.

If deactivated, this SoShadowGroup behaves like an SoGroup.

SoSFFloat SoShadowGroup::lightBleedingReduction

In some cases, a halo may appear around shadows intersecting each other.

Increasing this value will decrease this effect. Default value is safe for most scenes. Default is 0.01 and range is [0-1].

NOTE: field available since Open Inventor 8.1

SoSFEnum SoShadowGroup::method

Specifies the shadowing technique to use.

Use enum ShadowingMethod. Default is VARIANCE_SHADOW_MAP.

NOTE: field available since Open Inventor 8.1

SoSFFloat SoShadowGroup::minVariance

Increasing this value will decrease possible self-shadowing artifacts but will make shadows fade away.

The default value is safe for most scenes. Increasing the quality field is also preferable before tweaking this value. A special case is for SoVolumeRender node which has a minimum of 0.001 or IVVR_SHADOW_MIN_VARIANCE if set. Default is 1e-5 and range is [0-1].

NOTE: field available since Open Inventor 8.1

SoSFFloat SoShadowGroup::precision

Specifies the precision of the shadow.

0 = lowest precision, 1 = highest precision. With lower precisions, some parts of the scene may be unlit where they should be lit, or vice versa. Increasing the precision will reduce performance.

NOTE: If your graphics driver does not support the required OpenGL extensions, you may see low precision results even when this field is set to the highest precision.

SoSFFloat SoShadowGroup::quality

Specifies the quality of the shadow.

The texture used for shadowmap rendering will be of size 2*quality*ViewportSize. Increasing the quality will reduce performance and increase memory consumption.

SoSFBool SoShadowGroup::shadowCachingEnabled

Indicates if a cache should be used for computing the shadows.

Using a cache will improve rendering performance if the lights of your scene and your scene under this group node do not change.

SoSFInt32 SoShadowGroup::smoothFactor

Set the smoothness of shadows.

Higher values give smoother shadows. Default is 1.

NOTE: field available since Open Inventor 8.1

SoSFEnum SoShadowGroup::visibilityFlag

Specifies how visibilityRadius is interpreted.

Use enum VisibilityFlag. Default is LONGEST_BBOX_EDGE_FACTOR.

SoSFFloat SoShadowGroup::visibilityRadius

Shadows are only computed within "visibility radius" distance from the camera position.