rom/graphics/qbsblit.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Queue a beam-synchronized Blit
   6     Lang: english
   7 */
   8
   9 #include <proto/exec.h>
  10 #include <hardware/blit.h>
  11 #include <graphics/gfxbase.h>
  12
  13 /*****************************************************************************
  14
  15     NAME */
  16 #include <proto/graphics.h>
  17
  18         AROS_LH1(void, QBSBlit,
  19
  20 /*  SYNOPSIS */
  21         AROS_LHA(struct bltnode *, bn, A1),
  22
  23 /*  LOCATION */
  24         struct GfxBase *, GfxBase, 49, Graphics)
  25
  26 /*  FUNCTION
  27         Queues a request for a beam-synchronized  blit.
  28
  29     INPUTS
  30         bn - pointer to blitnode structure
  31
  32     RESULT
  33         The routine that function in the bltnode is pointing to is
  34         called when the blitter is ready for work. No other task will
  35         be able to access the blitter while you're doing the blit.
  36         Queued blits have precedence over a task that tries to own the
  37         blitter via OwnBlitter(). So all queued blitter requests will
  38         be done first until the task that attempts a OwnBlitter can
  39         actually access the blitter.
  40
  41     NOTES
  42         Not all hardware has a blitter. On hardware where there is no
  43         blitter, a blitter is simulated. Therefore all code that will
  44         be executed in the function that is called must not contain
  45         code that is hacking the blitter's register but should contain
  46         calls to graphics functions instead.
  47
  48     EXAMPLE
  49
  50     BUGS
  51
  52     SEE ALSO
  53         QBSBlit() OwnBlitter DisownBlitter() hardware/blit.h
  54
  55     INTERNALS
  56
  57     HISTORY
  58
  59 ******************************************************************************/
  60 {
  61   AROS_LIBFUNC_INIT
  62
  63   /* this function uses the queue bsblthd (bsblttl) */
  64
  65   /* I am accessing a public structure and there's no semaphore...*/
  66   Forbid();
  67
  68   if (NULL == GfxBase->bsblthd)
  69   {
  70     /* it's the first one in the list */
  71     GfxBase->bsblthd = bn;
  72     GfxBase->bsblttl = bn;
  73
  74     /* In this case the following also has to happen:
  75        It is my understanding that at the end of every blit an interrupt
  76        occurs that can take care of any blits in this queue or allow
  77        a taks to wake up when it was blocked due to a call to OwnBlitter.
  78        But in this case there might not be such an interrupt for a long
  79        time if no calls to blitterfunctions are made. Therefore this
  80        blit might be queued forever. To avoid this I have to cause
  81        a Blitter interrupt, if no task owns the blitter right now.
  82        (BlitOwner)
  83     */
  84     /*
  85       !!! missing code here!! See explanation above!
  86     */
  87   }
  88   else
  89   {
  90     /* queue it at the end */
  91     GfxBase->bsblttl->n = bn;
  92     GfxBase->bsblttl    = bn;
  93   }
  94
  95   Permit();
  96
  97   AROS_LIBFUNC_EXIT
  98
  99 } /* QBSBlit */