readso(3G)

NAME
     readso - sets the source for pixels that various routines read

FORTRAN 77 SPECIFICATION
     subroutine readso(src)
     integer*4 src

PARAMETERS
     src   expects a symbolic constant that identifies the pixel source that
           is to be used:

           SRCAUT selects the front color buffer when the current framebuffer,
           as specified by drawmo, is in single buffer mode. It selects the
           back color buffer when the current framebuffer is in double buffer
           mode.  This is the default.

           SRCFRO selects the front color buffer of the current framebuffer,
           as specified by drawmo.  This source is valid for both single
           buffer and double buffer operation.

           SRCBAC selects the back color buffer of the current framebuffer, as
           specified by drawmo.  This source is valid only while the current
           framebuffer is in double buffer mode.

           SRCZBU selects the z-buffer of the current framebuffer.  Because
           only the normal framebuffer has a z-buffer, this source is
           currently valid only while draw mode is NORMAL.

           SRCFRA selects the Live Video Digitizer as the pixel source,
           regardless of the current draw mode.  This source is valid only on
           IRIS-4D GTX and VGX models with the Live Video Digitizer option
           board.  IRIS-4D GTX models support this source only during rectco,
           not rectre or lrectr.

           SRCOVE selects the overlay planes, and is valid only while draw
           mode is NORMAL.  This source is valid only on the Personal Iris.

           SRCUND selects the underlay planes, and is valid only while draw
           mode is NORMAL.  This source is valid only on the Personal Iris.

           SRCPUP selects the pop-up planes, and is valid only while draw mode
           is NORMAL.  This source is valid only on the Personal Iris.

           selects the ilbuffers previously allocated with ilbuffer.  This
           source is valid only on the RealityEngine systems running 5.0.1 or
           later.

DESCRIPTION
     readso specifies the pixel source buffer that rectco, readpi, readRG,
     rectre, and lrectr  use. A separate read source is maintained for each of
     the GL framebuffers:  normal, pop-up, overlay, and underlay.  Calls to
     readso change the read source of the currently active framebuffer, as
     specified by drawmo.  By default the read source for each framebuffer is
     SRCAUT.

     Because read sources, with the exception of some implemented only on the
     Personal Iris, always specify a source within the current framebuffer, it
     is not possible to copy pixels from one framebuffer to another.  Such a
     copy must be implemented by first reading pixels out of the source
     framebuffer, then changing the draw mode to the destination framebuffer,
     and writing the pixels.

SEE ALSO
     lrectr, readpi, readRG, rectco

NOTES
     This subroutine is available only in immediate mode.

     On the IRIS-4D B or G models, SRC_ZBUFFER is not available.

     Read sources SRCOVE, SRCUND, and SRCPUP operate only on the Personal
     Iris.

BUGS
     On the IRIS-4D GT and GTX models, and on all Personal IRIS, XS, XS24, XZ,
     Elan and Extreme systems, a single variable is shared between the four
     framebuffers.

     On the Personal Iris, the source for pixel reads does not change when
     changing framebuffers (via drawmo) unless the current selected read
     source is SRCAUT (the default).

     On some IRIS-4D GT and GTX models, while copying rectangles with blending
     active, readso also specifies the bank from which destination color and
     alpha are read (overriding the blendf setting).