rom/graphics/scalerdiv.c

   1 /*
   2     Copyright © 1995-2001, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Graphics function ScalerDiv()
   6     Lang: english
   7 */
   8
   9 /*****************************************************************************
  10
  11     NAME */
  12 #include <proto/graphics.h>
  13
  14         AROS_LH3(UWORD, ScalerDiv,
  15
  16 /*  SYNOPSIS */
  17         AROS_LHA(UWORD, factor, D0),
  18         AROS_LHA(UWORD, numerator, D1),
  19         AROS_LHA(UWORD, denominator, D2),
  20
  21 /*  LOCATION */
  22         struct GfxBase *, GfxBase, 114, Graphics)
  23
  24 /*  FUNCTION
  25         Use this to precalculate the width/height of the destination
  26         bitmap. As factor give the width/height of the original bitmap
  27         that is to be scaled via ScaleBitMap(), as numerator give
  28         the value you will write into bsa_XSrcFactor/bsa_YSrcFactor
  29         and as denominator the value of bsa_XDestFactor/bsa_YDestFactor.
  30
  31     INPUTS
  32         factor      - a number in the range of 0..16383
  33         numerator   - a number in the range of 1..16383
  34         denominator - a number in the range of 1..16383
  35
  36     RESULT
  37
  38     NOTES
  39
  40     EXAMPLE
  41
  42     BUGS
  43
  44     SEE ALSO
  45         BitMapScale()
  46
  47     INTERNALS
  48
  49     HISTORY
  50
  51 *****************************************************************************/
  52 {
  53   AROS_LIBFUNC_INIT
  54   AROS_LIBBASE_EXT_DECL(struct GfxBase *,GfxBase)
  55
  56   ULONG res;
  57   if (0 == factor)
  58     return 0;
  59   else
  60     res = (ULONG)((ULONG)factor * (ULONG)numerator) / denominator;
  61
  62   if (0 == res)
  63     return 1;
  64
  65   if (((factor * numerator) % denominator) >= ((denominator + 1) >> 1))
  66     res++;
  67
  68   return res;
  69
  70   AROS_LIBFUNC_EXIT
  71 } /* ScalerDiv */