vga_runinbackground(3)						Svgalib User Manual					    vga_runinbackground(3)

NAME

       vga_runinbackground - enable running of the program while there is no VGA access

SYNOPSIS

       #include <vga.h>

       void vga_runinbackground(int stat);

DESCRIPTION

       Enable/disable background running of a graphics program.

       stat = 1
	      enables

       stat = 0
	      disables

       Normally,  the program is suspended while not in the current virtual console. A program can only safely run in the background if it doesn't
       do any video access during this time.

       As of version 1.2.11 this was changed by Pekka T. Alaruikka <alaruik@cc.hut.fi> & Michael Friman <no email> The support for  this  must	be
       enabled	in Makefile.cfg of svgalib (which it is by default). Several ways to support this may exist internally.  As of now, only one using
       proc-fs works.  Using vga_runinbackground(VGA_GOTOBACK, void (*goto)()) and vga_runinbackground(VGA_COMEFROMBACK, void (*comefrom)())  with
       function  pointers to functions void goto(void) and void comefrom(void) you can setup function to be called when your program goes to back-
       ground mode and when it comes back to foreground. These can be changed at any time, and passing NULL as function disables the feature.

       Both these new features require a vga_runinbackground_version(3) of 1 or higher. You should check and not call it when the svgalib  in  use
       returns 0.  Also, when writing applications, check with

       #ifdef VGA_GOTOBACK
	   /* code using vga_runinbackground(VGA_GOTOBACK, goto) */
       #else
	   /* code using no goto or comefrom function */
       #endif

       if  you	are compiling with an svgalib that supports this feature, and try to rearrange your source to work without it when an svgalib ver-
       sion prior to 1.2.11 is used.

       The function should be called right after vga_init(3).  The bg_test(6) demos shows the principle operation.

       Please note that background capabilities are in VERY early stages. Please do not expect that EVERYTHING works  flawlessly  when	background
       abilities are enabled in your program.

EXAMPLE

       vga_init();
       vga_setmode(G320x200x256);
       if (vga_runinbackground_version() == 1)
	    vga_runinbackground(1);

NOTES

       Before a program is left background capable, it should be tested well. Most programs will work just well.

       When the program is in background, it can read IO-devices (except keyboard).  This can cause harm, if the programmer does not take this int
       account. I.e. in games using a joystick or/and mouse device the game continues reading joystick or/and mouse as it would be on foreground.

       The mouse can be made working correctly also in background, but this means that svgalib must be configured to use gpm mouse driver.

       More information about gpm-linux can be founded from latest gpm packet (by Alessandro Rubini).

       The goto and comefrom routines provide a way to overcome this restriction.

       There are so far two different methods for background running. The first method use mmap function with FIXED option, which  is  not  recom-
       mended by mmap's man page.  It has some probability to fail. But it allows programs to think that graphics memory is always present.

       The second method is just let the functions to write directly graphics memory's save-buffer. This means that the memory area where graphics
       information is changes for the program. The program must always know where to write. This type of action needs much more  work  and  leaves
       probably always room for race conditions.

       Hopefully the first method proves to be good enough and second method can be left away.

       Neither	method	allows the use of the graphics card's registers in background.	When registers are used, vc switching is disabled, but the
       request are queued.  Vc switching is done as soon as possible.

       Generally, accelerated functions will probably cause problems, except when they are implemented carefully to check for availability of  the
       cards registers.

       User programs should generally not use the graphics registers directly. But if program needs to use the registers, it has to check if it is
       in background or not. In the background state it can not use the registers. For testing the vga_oktowrite(3) function can be  used.  During
       register access the virtual console must be locked. A possible code fragment might look like:

       vga_lockvc();
       if (vga_oktowrite()) {
	  /* Register operations. */
       } else {
	  /* Registers can not be used. Alternative action. */
       }
       vga_unlockvc();

ADVANCED NOTES

   Installation
       Background capability is enabled in svgalib by setting BACKGROUND=y and disabled by commenting #BACKGROUND=y in Makefile.cfg before compil-
       ing svgalib. Background capable svgalib is more stable with all programs. Programs do not have to use background abilities even	when  they
       are available. As of this writing, all precompiled svgalib binaries are background capable by default.  NOTICE: proc-fs must be mounted for
       background capability.

   Status of the background feature
       Background capability in svgalib is in an early stagei of development.  There has been done lot of work for it, but probably not everything
       will work perfectly. This applies only to programs which actually enabled background running with vga_runinbackground(3).

       The   vga_drawline(3),	vga_drawpixel(3),   vga_getclolors(3),	vga_getpixel(3),  vga_screenoff(3),  vga_screenon(3),  vga_setegacolor(3),
       vga_setrgbcolor(3), vga_setcolor(3), vga_setpage(3) and vga_clear(3) functions appear to work and calling vga_setmode(3) is  safe  too  but
       cannot change modes while in background. The remaining svgalib and vgagl function should work too but are not well tested.

       Calling accelerated functions will most probably cause harm though this is worked on.

       Please report problems to Pekka (see AUTHOR section).

   Programming within svgalib
       When  coding  within  svgalib,  there  are  same restrictions as in user programs.  SVGA registers can not be used while in background. The
       svgalibrary  has  internal  functions  for  locking  and   unlocking   virtual	console   switching   __svgalib_dont_switch_vt_yet()   and
       __svgalib_is_vt_switching_needed().   These  functions  are  not  meant to be called from user program.	vga_unlockvc(3) can not release vc
       switching if internal svgalib locking is used. This is for safety.  The procedure for registers are similar to the procedure for user  pro-
       grams:

       void vga_super_new_function(void) {
	   __svgalib_dont_switch_vt_yet();
	   if (vga_oktowrite()) {
	       /* Register operations. */
	   } else {
	       /* Registers can not be used. Alternative action. */
	   }
	   __svgalib_is_vt_switching_needed();
       }

SEE ALSO

       svgalib(7),  vgagl(7),  libvga.config(5),  bg_test(6),  vga_accel(3),  vga_bitblt(3), vga_blitwait(3), vga_fillblt(3), vga_hlinelistblt(3),
       vga_imageblt(3),  vga_init(3),  vga_lockvc(3),  vga_oktowrite(3),  vga_runinbackground_version(3),  vga_safety_fork(3),	vga_setchipset(3),
       vga_setpage(3), vga_setreadpage(3), vga_setwritepage(3), vga_unlockvc(3)

AUTHOR

       This  manual  page  was	edited	by  Michael Weller <eowmob@exp-math.uni-essen.de>. The function was implemented and documented by Pekka T.
       Alaruikka <alaruik@cc.hut.fi> & Michael Friman <no email>.

Svgalib (>;= 1.2.11)						   27 July 1997 					    vga_runinbackground(3)