fglPixelZoom(3G)

NAME
     fglPixelZoom - specify the pixel zoom factors


FORTRAN SPECIFICATION
     SUBROUTINE fglPixelZoom( REAL*4 xfactor,
                              REAL*4 yfactor )


PARAMETERS
     xfactor, yfactor Specify the x and y zoom factors for pixel write
                      operations.

DESCRIPTION
     fglPixelZoom specifies values for the x and y zoom factors.  Let, (x ,
                                                                         r
     y ) be the current raster position, and let interlace be either 1 or 2
      r
     corresponding to whether GL_INTERLACE_SGIX is enabled or not,
     respectively.  Then, during the execution of fglDrawPixels or
     fglCopyPixels, for a pixel that is in the mth row and nth column of the
     source image, the destination pixels that are candidate for replacement
     are those whose centers are on the bottom or left edge of, or inside the
     rectangle with corners at
     (x  + n x xfactor, y  + m x interlace x yfactor) and
       r                 r
     (x  + (n + 1) x xfactor,y  + (m x interlace + 1) x yfactor)
       r                      r

     Pixel zoom factors are not limited to positive values.  Negative zoom
     factors reflect the resulting image about the current raster position.

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

ASSOCIATED GETS
     fglGet with argument GL_ZOOM_X
     fglGet with argument GL_ZOOM_Y
     fglGet with argument GL_INTERLACE_SGIX


MACHINE DEPENDENCIES
     The SGIX_interlace extension is supported only on InfiniteReality
     systems, on RealityEngine, RealityEngine2, and VTX systems, and on O2
     systems.

     On InfiniteReality systems, the absolute values of the zoom factors must
     be strictly less than 128.  If not, they are clamped and GL_INVALID_VALUE
     is generated.

     Pixel zoom factors are snapped to fixed point precision on O2 systems,
     Indy and XL systems, XS, XZ, Elan, and Extreme systems.  fglGet will
     return these values.
SEE ALSO
     fglCopyPixels, fglEnable, fglDrawPixels.