fglSpriteParameterSGIX(3G)

NAME
     fglSpriteParameterfSGIX, fglSpriteParameteriSGIX,
     fglSpriteParameterfvSGIX, fglSpriteParameterivSGIX - set sprite
     parameters


FORTRAN SPECIFICATION
     SUBROUTINE fglSpriteParameterfSGIX( INTEGER*4 pname,
                                         REAL*4 param )
     SUBROUTINE fglSpriteParameteriSGIX( INTEGER*4 pname,
                                         INTEGER*4 param )


PARAMETERS
     pname   The parameter to be set. Must be GL_SPRITE_MODE_SGIX.

     param   The parameter value.  Must be one of GL_SPRITE_AXIAL_SGIX or
             GL_SPRITE_OBJECT_ALIGNED_SGIX or GL_SPRITE_EYE_ALIGNED_SGIX.



FORTRAN SPECIFICATION
     SUBROUTINE fglSpriteParameterfvSGIX( INTEGER*4 pname,
                                          CHARACTER*8 params )
     SUBROUTINE fglSpriteParameterivSGIX( INTEGER*4 pname,
                                          CHARACTER*8 params )


PARAMETERS
     pname
          The parameter to be set. Must be one of GL_SPRITE_MODE_SGIX or
          GL_SPRITE_AXIS_SGIX or GL_SPRITE_TRANSLATION_SGIX.

     params
          Must be a pointer to a scalar (GL_SPRITE_MODE_SGIX) or to a three-
          valued vector (GL_SPRITE_AXIS_SGIX or GL_SPRITE_TRANSLATION_SGIX for
          x, y, z, respectively).

DESCRIPTION
     fglSpriteParameterSGIX is part of the GL_SGIX_sprite extension.  This
     extension provides support for geometry that rotates to face the eye, in
     the manner of Iris Performer billboards.  This is most useful for fast
     approximate rendering of objects that have rough spherical or cylindrical
     symmetry, such as trees, smoke, and clouds, where the objects are modeled
     as simple geometry covered by a complex partially-transparent texture
     map.

     Sprite geometry is modelled in a canonical frame in which +Z is the up
     vector, and -Y is the front vector which is rotated to point to the eye.
     Rendering sprite geometry requires applying a transformation to
     primitives before applying the current modelview matrix.  This
     transformation is based on the current modelview matrix, the sprite
     rendering mode, and the constraints on sprite motion.

     fglSpriteParameterSGIX sets the value of a sprite parameter.  pname
     specifies the parameter to be changed.

     When pname is GL_SPRITE_MODE_SGIX, param specifies the sprite rendering
     mode.  param must be one of the following values:

     GL_SPRITE_AXIAL_SGIX
               The front of the object is rotated about an axis so that it
               faces the eye as much as the axis constraint allows.

     GL_SPRITE_OBJECT_ALIGNED_SGIX
               The front of the object is rotated about a point to face the
               eye. The remaining rotational degree of freedom is specified by
               aligning the top of the object with a specified axis in object
               coordinates.

     GL_SPRITE_EYE_ALIGNED_SGIX
               The front of the object is rotated about a point to face the
               eye. The remaining rotational degree of freedom is specified by
               aligning the top of the object with a specified axis in eye
               coordinates.

     When pname is either GL_SPRITE_AXIS_SGIX or GL_SPRITE_TRANSLATION_SGIX,
     params is a pointer to a four-element vector that specifies the sprite
     rotation axis or sprite translation, respectively.

     The rendering of sprite geometry is enabled with fglEnable and disabled
     with fglDisable using the constant GL_SPRITE_SGIX.

NOTES
     When using sprites, the current projection matrix must not include a
     rotation.

     Be aware that user-defined clipping planes, texture coordinates produced
     by certain fglTexGen modes, and the current raster position will be
     affected by the combined sprite and modelview transformation if they are
     specified while GL_SPRITE_SGIX is enabled.

     fglSpriteParameterSGIX is part of the GL_SGIX_sprite extension, not part
     of the core GL command set.  See fglIntro for information about using
     extensions.

ERRORS
     GL_INVALID_ENUM is generated if pname is not an accepted value.
     GL_INVALID_ENUM is generated if fglSpriteParameterfSGIX or
     fglSpriteParameteriSGIX parameter pname is the GL_SPRITE_MODE_SGIX and
     parameter param is not one of the accepted values.

     GL_INVALID_OPERATION is generated if fglSpriteParameterSGIX is executed
     between the execution of fglBegin and the corresponding execution of
     fglEnd.

ASSOCIATED GETS
     fglIsEnabled with argument GL_SPRITE_SGIX
     fglGet with argument GL_SPRITE_MODE_SGIX
     fglGet with argument GL_SPRITE_AXIS_SGIX
     fglGet with argument GL_SPRITE_TRANSLATION_SGIX
     fglGetString with argument GL_EXTENSIONS


SEE ALSO