libs/gfx/algo/FillEllipse.algo.h

   1 /*****************************************************************************
   2  * This file is part of gfxprim library.                                     *
   3  *                                                                           *
   4  * Gfxprim is free software; you can redistribute it and/or                  *
   5  * modify it under the terms of the GNU Lesser General Public                *
   6  * License as published by the Free Software Foundation; either              *
   7  * version 2.1 of the License, or (at your option) any later version.        *
   8  *                                                                           *
   9  * Gfxprim is distributed in the hope that it will be useful,                *
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of            *
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU         *
  12  * Lesser General Public License for more details.                           *
  13  *                                                                           *
  14  * You should have received a copy of the GNU Lesser General Public          *
  15  * License along with gfxprim; if not, write to the Free Software            *
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor,                        *
  17  * Boston, MA  02110-1301  USA                                               *
  18  *                                                                           *
  19  * Copyright (C) 2009-2010 Jiri "BlueBear" Dluhos                            *
  20  *                         <jiri.bluebear.dluhos@gmail.com>                  *
  21  *                                                                           *
  22  * Copyright (C) 2009-2010 Cyril Hrubis <metan@ucw.cz>                       *
  23  *                                                                           *
  24  *****************************************************************************/
  25
  26 /*
  27  * A filled ellipse drawing algorithm.
  28  *
  29  * The algorithm is exactly the same as with GP_Ellipse() except that
  30  * we draw a line between each two points at each side of the X axis;
  31  * therefore, we don't need to draw any points during iterations of X,
  32  * we just iterate X until Y reaches next line, and then draw the full line.
  33  */
  34
  35 /*
  36  * This macro defines a filled ellipse drawing function.
  37  * Arguments:
  38  *     CONTEXT_T - user-defined type of drawing context (passed to HLINE)
  39  *     PIXVAL_T  - user-defined pixel value type (passed to HLINE)
  40  *     HLINE     - horizontal line drawing function f(context, x0, x1, y, pixval)
  41  *     FN_NAME   - name of the function to be defined
  42  */
  43 #define DEF_FILLELLIPSE_FN(FN_NAME, CONTEXT_T, PIXVAL_T, HLINE) \
  44 void FN_NAME(CONTEXT_T context, int xcenter, int ycenter, \
  45         unsigned int a, unsigned int b, PIXVAL_T pixval) \
  46 { \
  47         /* Precompute quadratic terms. */ \
  48         int a2 = a*a; \
  49         int b2 = b*b; \
  50 \
  51         int x, y, error; \
  52         for (x = 0, error = -b2*a, y = b; y >= 0; y--) { \
  53                 while (error < 0) { \
  54                         error += b2 * (2*x + 1); \
  55                         x++; \
  56                 } \
  57                 error += a2 * (-2*y + 1); \
  58 \
  59                 /* Draw two horizontal lines reflected across Y. */ \
  60                 HLINE(context, xcenter-x+1, xcenter+x-1, ycenter-y, pixval); \
  61                 HLINE(context, xcenter-x+1, xcenter+x-1, ycenter+y, pixval); \
  62         } \
  63 }