- specify the raster position for pixel operations



C SPECIFICATION


PARAMETERS

       _param1, _param2, _param3, _param4
                                        Specify  the x, y, z, and
                                        w object coordinates  (if
                                        present)  for  the raster
                                        position.


C SPECIFICATION


PARAMETERS

       _param1
              Specifies a pointer to an array of two,  three,  or
              four  elements,  specifying  x, y, z, and w coordi-
              nates, respectively.


DESCRIPTION

       The GL maintains a  3D  position  in  window  coordinates.
       This  position,  called  the  raster  position, is used to
       position pixel and bitmap write operations.  It  is  main-
       tained    with    subpixel    accuracy.    See   glBitmap,
       glDrawPixels, and glCopyPixels.

       The current raster position consists of three window coor-
       dinates  (x,  y,  z),  a clip coordinate value (w), an eye
       coordinate distance, a valid  bit,  and  associated  color
       data  and texture coordinates.  The w coordinate is a clip
       coordinate, because w is not projected to  window  coordi-
       nates.  glRasterPos4 specifies object coordinates x, y, z,
       and w explicitly.  glRasterPos3 specifies  object  coordi-
       nate  x, y, and z explicitly, while w is implicitly set to
       1.  glRasterPos2 uses the argument  values  for  x  and  y
       while implicitly setting z and w to 0 and 1.

       The   object  coordinates  presented  by  glRasterPos  are
       treated just like those of a glVertex  command:  They  are
       transformed by the current modelview and projection matri-
       ces and passed to the clipping stage.  If  the  vertex  is
       not  culled,  then  it  is  projected and scaled to window
       coordinates, which become the new current raster position,
       and  the GL_CURRENT_RASTER_POSITION_VALID flag is set.  If
       the vertex is culled, then the valid bit  is  cleared  and
       the  current raster position and associated color and tex-
       ture coordinates are undefined.

       The current raster position also includes some  associated
       color  data  and  texture  coordinates.   If  lighting  is
       enabled, then GL_CURRENT_RASTER_COLOR (in  RGBA  mode)  or
       GL_CURRENT_RASTER_INDEX  (in  color  index mode) is set to
       the  color  produced  by  the  lighting  calculation  (see
       the  current  raster  distance is 0, the valid bit is set,
       the associated RGBA color is (1, 1, 1, 1), the  associated
       color  index  is 1, and the associated texture coordinates
       are (0, 0, 0, 1).  In RGBA  mode,  GL_CURRENT_RASTER_INDEX
       is  always 1; in color index mode, the current raster RGBA
       color always maintains its initial value.


NOTES

       The raster position is modified both by glRasterPos and by
       glBitmap.

       When  the raster position coordinates are invalid, drawing
       commands that are based on the raster position are ignored
       (that is, they do not result in changes to GL state).

       Calling  glDrawElements,  or glDrawRangeElements may leave
       the current color or index indeterminate.  If  glRasterPos
       is executed while the current color or index is indetermi-
       nate, the current raster color  or  current  raster  index
       remains indeterminate.

       To set a valid raster position outside the viewport, first
       set a valid raster position, then call glBitmap with  NULL
       as the bitmap parameter.

       When  the GL_ARB_imaging extension is supported, there are
       distinct raster texture coordinates for each texture unit.
       Each  texture  unit's  current ratster texture coordinates
       are updated by glRasterPos.


ERRORS

       GL_INVALID_OPERATION is generated if glRasterPos  is  exe-
       cuted between the execution of glBegin and the correspond-
       ing execution of glEnd.


ASSOCIATED GETS

       glGet with argument GL_CURRENT_RASTER_POSITION
       glGet with argument GL_CURRENT_RASTER_POSITION_VALID
       glGet with argument GL_CURRENT_RASTER_DISTANCE
       glGet with argument GL_CURRENT_RASTER_COLOR
       glGet with argument GL_CURRENT_RASTER_INDEX
       glGet with argument GL_CURRENT_RASTER_TEXTURE_COORDS


SEE ALSO

       glBitmap,  glCopyPixels,   glDrawArrays,   glDrawElements,
       glDrawRangeElements,  glDrawPixels,  glTexCoord, glTexGen,
       glVertex



                                                                1