rom/graphics/scalerdiv.c

   1 /*
   2     Copyright © 1995-2007, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Graphics function ScalerDiv()
   6     Lang: english
   7 */
   8
   9 #include "graphics_intern.h"
  10
  11 /*****************************************************************************
  12
  13     NAME */
  14 #include <proto/graphics.h>
  15
  16         AROS_LH3(UWORD, ScalerDiv,
  17
  18 /*  SYNOPSIS */
  19         AROS_LHA(UWORD, factor, D0),
  20         AROS_LHA(UWORD, numerator, D1),
  21         AROS_LHA(UWORD, denominator, D2),
  22
  23 /*  LOCATION */
  24         struct GfxBase *, GfxBase, 114, Graphics)
  25
  26 /*  FUNCTION
  27         Use this to precalculate the width/height of the destination
  28         bitmap. As factor give the width/height of the original bitmap
  29         that is to be scaled via ScaleBitMap(), as numerator give
  30         the value you will write into bsa_XSrcFactor/bsa_YSrcFactor
  31         and as denominator the value of bsa_XDestFactor/bsa_YDestFactor.
  32
  33     INPUTS
  34         factor      - a number in the range of 0..16383
  35         numerator   - a number in the range of 1..16383
  36         denominator - a number in the range of 1..16383
  37
  38     RESULT
  39
  40     NOTES
  41
  42     EXAMPLE
  43
  44     BUGS
  45
  46     SEE ALSO
  47         BitMapScale()
  48
  49     INTERNALS
  50
  51     HISTORY
  52
  53 *****************************************************************************/
  54 {
  55   AROS_LIBFUNC_INIT
  56
  57   ULONG res;
  58   if (0 == factor || 0 == numerator || 0 == denominator)
  59     return 0;
  60   else
  61     res = (ULONG)((ULONG)factor * (ULONG)numerator) / denominator;
  62
  63   if (0 == res)
  64     return 1;
  65
  66   if (((factor * numerator) % denominator) >= ((denominator + 1) >> 1))
  67     res++;
  68
  69   return res;
  70
  71   AROS_LIBFUNC_EXIT
  72 } /* ScalerDiv */