libs/gfx/algo/Arc.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) 2009-2012 Cyril Hrubis <metan@ucw.cz>                       *
  23  *                                                                           *
  24  *****************************************************************************/
  25
  26 /*
  27  * The elliptical arc algorithm; a generalization of an ellipse that allows
  28  * to draw only part of it. The math is exactly the same, only it has
  29  * additional tests of what part to draw.
  30  */
  31
  32 /*
  33  * This macro defines a function that draws a segment of an arc within
  34  * two horizontal quadrants. For a larger arc, two calls are needed.
  35  *
  36  * The 'direction' parameter specifies which two quadrants to work in:
  37  * if <0, the top two quadrants (y < 0) are used, if >0, the bottom two
  38  * (y > 0) are used.
  39  *
  40  * Arguments:
  41  *     PIXMAP_T - user-defined type of drawing pixmap (passed to PUTPIXEL)
  42  *     PIXVAL_T  - user-defined pixel value type (passed to PUTPIXEL)
  43  *     PUTPIXEL  - a pixel drawing function f(pixmap, x, y, pixval)
  44  *     FN_NAME   - name of the function to be defined
  45  */
  46 #define DEF_ARCSEGMENT_FN(FN_NAME, PIXMAP_T, PIXVAL_T, PUTPIXEL) \
  47 static void FN_NAME(PIXMAP_T pixmap, int xcenter, int ycenter, \
  48         unsigned int a, unsigned int b, int direction, \
  49         double start, double end, PIXVAL_T pixval) \
  50 { \
  51         /* Precompute quadratic terms. */ \
  52         int a2 = a*a; \
  53         int b2 = b*b; \
  54 \
  55         /* Compute minimum and maximum value of X from the angles. */ \
  56         int x1 = (int)(cos(start)*a); \
  57         int x2 = (int)(cos(end)*a); \
  58         int xmin = GP_MIN(x1, x2); \
  59         int xmax = GP_MAX(x1, x2); \
  60 \
  61         int x, y, error; \
  62         for (x = 0, error = -b2*a, y = b; y >= 0; y--) { \
  63                 while (error < 0) { \
  64 \
  65                         /* Calculate error(x+1) from error(x). */ \
  66                         error += 2*x*b2 + b2; \
  67                         x++; \
  68 \
  69                         if (direction < 0) { \
  70                                 if ((-x+1) >= xmin && (-x+1) <= xmax) { \
  71                                         PUTPIXEL(pixmap, xcenter-x+1, ycenter-y, pixval); \
  72                                 } \
  73                                 if ((x-1) >= xmin && (x-1) <= xmax) { \
  74                                         PUTPIXEL(pixmap, xcenter+x-1, ycenter-y, pixval); \
  75                                 } \
  76                         } \
  77                         if (direction > 0) { \
  78                                 if ((-x+1) >= xmin && (-x+1) <= xmax) { \
  79                                         PUTPIXEL(pixmap, xcenter-x+1, ycenter+y, pixval); \
  80                                 } \
  81                                 if ((x-1) >= xmin && (x-1) <= xmax) { \
  82                                         PUTPIXEL(pixmap, xcenter+x-1, ycenter+y, pixval); \
  83                                 } \
  84                         } \
  85                 } \
  86 \
  87                 /* Calculate error(y-1) from error(y). */ \
  88                 error += -2*y*a2 + a2; \
  89 \
  90                 if (direction < 0) { \
  91                         if ((-x+1) >= xmin && (-x+1) <= xmax) { \
  92                                 PUTPIXEL(pixmap, xcenter-x+1, ycenter-y, pixval); \
  93                         } \
  94                         if ((x-1) >= xmin && (x-1) <= xmax) { \
  95                                 PUTPIXEL(pixmap, xcenter+x-1, ycenter-y, pixval); \
  96                         } \
  97                 } \
  98                 if (direction > 0) { \
  99                         if ((-x+1) >= xmin && (-x+1) <= xmax) { \
 100                                 PUTPIXEL(pixmap, xcenter-x+1, ycenter+y, pixval); \
 101                         } \
 102                         if ((x-1) >= xmin && (x-1) <= xmax) { \
 103                                 PUTPIXEL(pixmap, xcenter+x-1, ycenter+y, pixval); \
 104                         } \
 105                 } \
 106         } \
 107 }