libs/gfx/GP_LineClip.c

   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 #include "core/GP_Common.h"
  27 #include "core/GP_Types.h"
  28 #include "gfx/GP_LineClip.h"
  29
  30 int GP_LineClip(int *px0, int *py0, int *px1, int *py1, int xmax, int ymax)
  31 {
  32         float x0 = (float) *px0;
  33         float y0 = (float) *py0;
  34         float x1 = (float) *px1;
  35         float y1 = (float) *py1;
  36
  37         /* horizontal and vertical line are special cases */
  38         if (y0 == y1) {
  39
  40                 /* orient the line from left to right */
  41                 if (x1 < x0) {
  42                         GP_SWAP(x0, x1);
  43                         GP_SWAP(y0, y1);
  44                 }
  45
  46                 /* check if it is not completely outside */
  47                 if (x1 < 0 || x0 > xmax || y0 < 0 || y0 > ymax)
  48                         return 0;
  49
  50                 x0 = GP_MAX(x0, 0);
  51                 x1 = GP_MIN(x1, xmax);
  52                 goto give_result;
  53         }
  54         if (x0 == x1) {
  55
  56                 /* orient the line from top to down */
  57                 if (x1 < x0) {
  58                         GP_SWAP(x0, x1);
  59                         GP_SWAP(y0, y1);
  60                 }
  61
  62                 /* check if it is not completely outside */
  63                 if (y1 < 0 || y0 > ymax || x0 < 0 || x0 > xmax)
  64                         return 0;
  65
  66                 /* clip it to the valid range */
  67                 y0 = GP_MAX(y0, 0);
  68                 y1 = GP_MIN(y1, ymax);
  69                 goto give_result;
  70         }
  71
  72         /* orient the line from left to right */
  73         if (x1 < x0) {
  74                 GP_SWAP(x0, x1);
  75                 GP_SWAP(y0, y1);
  76         }
  77
  78         if (x1 < 0 || x0 > xmax || (y0 < 0 && y1 < 0) || (y0 > ymax && y1 > ymax)) {
  79
  80                 /* the line lies completely outside the rectangle */
  81                 return 0;
  82         }
  83
  84         float dx = (float)(x1 - x0);
  85         float dy = (float)(y1 - y0);
  86         float dyx = dy/dx;
  87         float dxy = dx/dy;
  88
  89         /* clip the line against the left and right side of the rectangle */
  90         if (x0 < 0) {
  91                 y0 = y0 - x0*dyx;
  92                 x0 = 0;
  93         }
  94         if (x1 > xmax) {
  95                 x1 = xmax;
  96                 y1 = y0 + (x1-x0)*dyx;
  97         }
  98
  99         if (y0 < 0.0f) {
 100                 x0 = x0 - y0*dxy;
 101                 y0 = 0.0f;
 102         } else if (y0 > ymax) {
 103                 x0 = x0 + (ymax-y0)*dxy;
 104                 y0 = ymax;
 105         }
 106
 107         if (y1 < 0.0f) {
 108                 x1 = x1 - y1*dxy;
 109                 y1 = 0.0f;
 110         }
 111         else if (y1 > ymax) {
 112                 x1 = x1 - (y1 - ymax)*dxy;
 113                 y1 = ymax;
 114         }
 115
 116         if (x0 < 0 || x0 > xmax || x1 < 0 || x1 > xmax) {
 117
 118                 /* the line misses the clip rectangle around the corner */
 119                 return 0;
 120         }
 121
 122 give_result:
 123
 124         *px0 = (int) x0;
 125         *py0 = (int) y0;
 126         *px1 = (int) x1;
 127         *py1 = (int) y1;
 128         return 1;
 129 }