git.sur5r.net Git - cc65/blob - libsrc/tgi/tgi_arc.c

   1 /*****************************************************************************/
   2 /*                                                                           */
   3 /*                                 tgi_arc.c                                 */
   4 /*                                                                           */
   5 /*                            Draw an ellipse arc                            */
   6 /*                                                                           */
   7 /*                                                                           */
   8 /*                                                                           */
   9 /* (C) 2002-2009, Ullrich von Bassewitz                                      */
  10 /*                Roemerstrasse 52                                           */
  11 /*                D-70794 Filderstadt                                        */
  12 /* EMail:         uz@cc65.org                                                */
  13 /*                                                                           */
  14 /*                                                                           */
  15 /* This software is provided 'as-is', without any expressed or implied       */
  16 /* warranty.  In no event will the authors be held liable for any damages    */
  17 /* arising from the use of this software.                                    */
  18 /*                                                                           */
  19 /* Permission is granted to anyone to use this software for any purpose,     */
  20 /* including commercial applications, and to alter it and redistribute it    */
  21 /* freely, subject to the following restrictions:                            */
  22 /*                                                                           */
  23 /* 1. The origin of this software must not be misrepresented; you must not   */
  24 /*    claim that you wrote the original software. If you use this software   */
  25 /*    in a product, an acknowledgment in the product documentation would be  */
  26 /*    appreciated but is not required.                                       */
  27 /* 2. Altered source versions must be plainly marked as such, and must not   */
  28 /*    be misrepresented as being the original software.                      */
  29 /* 3. This notice may not be removed or altered from any source              */
  30 /*    distribution.                                                          */
  31 /*                                                                           */
  32 /*****************************************************************************/
  33
  34
  35
  36 #include <tgi.h>
  37 #include <cc65.h>
  38
  39
  40
  41 /*****************************************************************************/
  42 /*                                   Code                                    */
  43 /*****************************************************************************/
  44
  45
  46
  47 static int RoundMul (int rhs, int lhs)
  48 {
  49     long res = cc65_imul16x16r32 (rhs, lhs);
  50     if ((unsigned char)res & 0x80) {
  51         return (int)(res >> 8) + 1;
  52     } else {
  53         return (int)(res >> 8);
  54     }
  55 }
  56
  57
  58
  59 void __fastcall__ tgi_arc (int x, int y, unsigned char rx, unsigned char ry,
  60                            unsigned sa, unsigned ea)
  61 /* Draw an ellipse arc with center at x/y and radii rx/ry using the current
  62  * drawing color. The arc covers the angle between sa and ea (startangle and
  63  * endangle), which must be in the range 0..360 (otherwise the function may
  64  * bevave unextectedly).
  65  */
  66 {
  67     int x1, y1, x2, y2;
  68     unsigned char inc;
  69     unsigned char done = 0;
  70
  71     /* Bail out if there's nothing to do */
  72     if (sa > ea) {
  73         return;
  74     }
  75
  76     /* Determine the number of segments to use. This may be refined ... */
  77     if (rx + ry >= 25) {
  78         inc = 12;
  79     } else {
  80         inc = 24;
  81     }
  82
  83     /* Calculate the start coords */
  84     x1 = x + RoundMul (rx, cc65_cos (sa));
  85     y1 = y + RoundMul (ry, cc65_sin (sa));
  86     do {
  87         sa += inc;
  88         if (sa >= ea) {
  89             sa = ea;
  90             done = 1;
  91         }
  92         x2 = x + RoundMul (rx, cc65_cos (sa));
  93         y2 = y - RoundMul (ry, cc65_sin (sa));
  94         tgi_line (x1, y1, x2, y2);
  95         x1 = x2;
  96         y1 = y2;
  97     } while (!done);
  98 }
  99
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