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drawmode(3G)							  drawmode(3G)

NAME    [Toc]    [Back]

     drawmode -	selects	which GL framebuffer is	drawable

C SPECIFICATION    [Toc]    [Back]

     void drawmode(mode)
     long mode;

PARAMETERS    [Toc]    [Back]

     mode   expects the	identifier of the framebuffer to which GL drawing
	    commands are to be directed:

	    NORMALDRAW,	which sets operations for the normal color and z
	    buffer bitplanes.

	    OVERDRAW, which sets operations for	the overlay bitplanes.

	    UNDERDRAW, which sets operations for the underlay bitplanes.

	    PUPDRAW, which sets	operations for the pop-up bitplanes.

	    CURSORDRAW,	which sets operations for the cursor.

DESCRIPTION    [Toc]    [Back]

     The IRIS physical framebuffer is divided into 4 separate GL framebuffers:
     pop-up, overlay, normal, and underlay.  drawmode specifies	which of these
     four buffers is currently being controlled	and modified by	GL drawing and
     mode commands.  Because drawmode cannot be	set to multiple	framebuffers,
     GL	drawing	commands affect	only one of the	four GL	framebuffers at	a

     The way that GL modes interact with drawmode is both complex and
     significant to the	GL programmer.	For example, each framebuffer
     maintains its own current color and its own color map, but	linewidth is
     shared among all framebuffers.  In	general, modes that determine what is
     to	be drawn into the framebuffers are shared; modes that control
     framebuffer resources are either multiply specified, or specified only
     for the normal framebuffer.

     A separate	version	of each	of the following modes is maintained by	each
     GL	framebuffer.  These modes are modified and read	back based on the
     current draw mode:

	  color	or RGBcolor
	  mapcolor (a separate color map per framebuffer)
	  writemask or RGBwritemask

									Page 1

drawmode(3G)							  drawmode(3G)

     The following modes currently affect only the operation of	the normal
     framebuffer.  They	must therefore be modified only	while draw mode	is
     NORMALDRAW.  As features are added	to the GL, these modes may become
     available in other	draw modes.  When this happens,	a separate mode	will
     be	maintained for each draw mode.


     All other modes, including	matrices, viewports, graphics and character
     positions,	lighting, and many primitive rendering options,	are shared by
     the four GL framebuffers.

     Draw mode CURSORDRAW differs from the others.  True bitplanes for the
     cursor do not exist; there	is no current color or writemask in this
     drawing mode.  However, the cursor	does have its own color	map, and when
     in	this mode, mapcolor and	getmcolor access it.

SEE ALSO    [Toc]    [Back]

     acsize, cmode, c, color, cpack, gconfig, getcolor,	getmcolor,
     getwritemask, mapcolor, overlay, stencil, underlay, wmpack, writemask

NOTES    [Toc]    [Back]

     This routine is available only in immediate mode.

     Some GL modes that	are shared by all draw modes are not implemented by
     the popup,	overlay, or underlay framebuffers.  For	example, the Personal
     Iris does not do Gouraud shading in these framebuffers.  It is important
     for the programmer	to explicitly disable modes that are shared, but not
     desired, when in draw modes other than NORMALDRAW.	 Otherwise the code
     may function differently on different platforms.

     Iris Entry	graphics do not	support	OVERDRAW or UNDERDRAW draw modes.  Use
     getgdesc to determine the number of bitplanes available for OVERDRAW or
     UNDERDRAW on any machine.

									PPPPaaaaggggeeee 2222
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