rom/graphics/ownblitter.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Try to own the blitter for private usage
   6     Lang: english
   7 */
   8
   9 #include <proto/exec.h>
  10 #include <graphics/gfxbase.h>
  11 #include <exec/execbase.h>
  12 #include <exec/tasks.h>
  13
  14 /*****************************************************************************
  15
  16     NAME */
  17 #include <proto/graphics.h>
  18
  19         AROS_LH0(void, OwnBlitter,
  20
  21 /*  SYNOPSIS */
  22
  23
  24 /*  LOCATION */
  25         struct GfxBase *, GfxBase, 76, Graphics)
  26
  27 /*  FUNCTION
  28         The blitter is allocated for exclusive use by the calling task.
  29         This function returns immediately if no other task is using
  30         the blitter right now or if no blits are in the queues (QBlit(),
  31         QBSBlit()). Otherwise the function will block until the blitter
  32         can be accessed.
  33         It is good practice to start the blitter immediately after calling
  34         this function and then call DisownBlitter() so other tasks can
  35         use the blitter.
  36
  37     INPUTS
  38
  39     RESULT
  40
  41     NOTES
  42
  43     EXAMPLE
  44
  45     BUGS
  46
  47     SEE ALSO
  48         DisownBlitter()
  49
  50     INTERNALS
  51
  52     HISTORY
  53
  54 ******************************************************************************/
  55 {
  56   AROS_LIBFUNC_INIT
  57
  58   /* prevent other tasks from doing what I am doing */
  59   struct Task * me;
  60
  61   me  = FindTask(NULL);
  62
  63   Forbid();
  64
  65   /* test whether a task is using the blitter. Even if the blitter is
  66      used by the queued blits now the BlitOwner entry must not be NULL!
  67    */
  68
  69   if (NULL == GfxBase->BlitOwner)
  70   {
  71     /* nobody is using the blitter right now, so I can use it */
  72     GfxBase->BlitOwner=me;
  73   }
  74   else
  75   {
  76     BOOL first = TRUE;
  77     /* the blitter is used. I have to set this task asleep and queue
  78        it into the BlitWaitQ.
  79     */
  80
  81     /* Repeat this as long as there is somebody else using the blitter.
  82        This is necessary as when the other task calls DisownBlitter() it
  83        might take a while until this task gets to run again and
  84        yet another taks might issue QBlit() in the meantime and the blitter
  85        might be busy with that. So this task will have to wait again.
  86        However at the first call this task is put to the end of the waiting
  87        list and after that it is always put at the very front.
  88     */
  89     while (NULL != GfxBase->BlitOwner)
  90     {
  91       /* force this task to sleep */
  92
  93       BYTE old_TDNestCnt = SysBase->TDNestCnt;
  94       SysBase->TDNestCnt=-1;
  95
  96       /*
  97          Move it to the waiting list in the GfxBase structure.
  98          It will be moved to the ready list by the blitterinterrupt
  99          handler.
 100       */
 101       if (first)
 102       {
 103         AddTail(&GfxBase->BlitWaitQ, &me->tc_Node);
 104         /* The next time I will put this task  at the beginning
 105            of the list, if necessary.
 106         */
 107         first = FALSE;
 108       }
 109       else
 110       {
 111         AddHead(&GfxBase->BlitWaitQ, &me->tc_Node);
 112       }
 113
 114       /* Switch to the next ready task. */
 115       Switch();
 116       /*
 117         OK. Somebody awakened me. This means that I the task might now
 118         have full control over the blitter. Checking is in the while-loop.
 119       */
 120
 121       /* Restore TDNestCnt. */
 122       SysBase->TDNestCnt=old_TDNestCnt;
 123     } /* while () */
 124     /* I am the owner now !! */
 125     Disable();
 126     GfxBase -> BlitOwner = me;
 127     Enable();
 128   }
 129
 130   Permit();
 131
 132   AROS_LIBFUNC_EXIT
 133 } /* OwnBlitter */