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comparison src/video/SDL_rect.c @ 2994:7563b99e9a49

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Date: Sat, 3 Jan 2009 22:11:18 -0500 From: "Donny Viszneki" Subject: Re: [SDL] Want to help with SDL 1.3? >> > For example, here's a good quick project for someone from the TODO list: >> > * Add diagonal line clipping to SDL_IntersectRectAndLine() Just wanted to point out that the patch is available at http://codebad.com/rect-line-ix.patch I hereby grant Sam Lantinga an irrevocable non-exclusive distribution license to this patch to do with as he wishes.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 04 Jan 2009 19:33:21 +0000
parents cdb01906cb7e
children e4f025078c1c
comparison
equal deleted inserted replaced
2993:2fad80c77c17 2994:7563b99e9a49
146 if (x1 >= rectx1 && x1 <= rectx2 && x2 >= rectx1 && x2 <= rectx2 && 146 if (x1 >= rectx1 && x1 <= rectx2 && x2 >= rectx1 && x2 <= rectx2 &&
147 y1 >= recty1 && y1 <= recty2 && y2 >= recty1 && y2 <= recty2) { 147 y1 >= recty1 && y1 <= recty2 && y2 >= recty1 && y2 <= recty2) {
148 return SDL_TRUE; 148 return SDL_TRUE;
149 } 149 }
150 150
151 /* Check to see if entire line is outside rect */ 151 /* Check to see if entire line is to one side of rect */
152 if ((x1 < rectx1 && x2 < rectx1) || (x1 > rectx2 && x2 > rectx2) || 152 if ((x1 < rectx1 && x2 < rectx1) || (x1 > rectx2 && x2 > rectx2) ||
153 (y1 < recty1 && y2 < recty2) || (y1 > recty2 && y2 > recty2)) { 153 (y1 < recty1 && y2 < recty2) || (y1 > recty2 && y2 > recty2)) {
154 return SDL_FALSE; 154 return SDL_FALSE;
155 } 155 }
156 156
157 if (y1 = y2) { 157 if (y1 == y2) {
158 /* Horizontal line, easy to clip */ 158 /* Horizontal line, easy to clip */
159 if (x1 < rectx1) { 159 if (x1 < rectx1) {
160 *X1 = rectx1; 160 *X1 = rectx1;
161 } else if (x1 > rectx2) { 161 } else if (x1 > rectx2) {
162 *X1 = rectx2; 162 *X1 = rectx2;
182 *Y2 = recty2; 182 *Y2 = recty2;
183 } 183 }
184 return SDL_TRUE; 184 return SDL_TRUE;
185 } 185 }
186 186
187 /* FIXME: need code to clip diagonal line to rect */ 187 else
188 {
189 /* The task of clipping a line with finite slope ratios in a fixed-
190 * precision coordinate space is not as immediately simple as it is
191 * with coordinates of arbitrary precision. If the ratio of slopes
192 * between the input line segment and the result line segment is not
193 * a whole number, you have in fact *moved* the line segment a bit,
194 * and there can be no avoiding it without more precision
195 */
196 int *x_result_[] = {X1, X2, NULL}, **x_result = x_result_;
197 int *y_result_[] = {Y1, Y2, NULL}, **y_result = y_result_;
198 SDL_bool intersection = SDL_FALSE;
199 double b, m, left, right, bottom, top;
200 int xl, xh, yl, yh;
201
202 /* solve mx+b line formula */
203 m = (double)(y1-y2) / (double)(x1-x2);
204 b = y2 - m * (double) x2;
205
206 /* find some linear intersections */
207 left = (m * (double) rectx1) + b;
208 right = (m * (double) rectx2) + b;
209 top = (recty1 - b) / m;
210 bottom = (recty2 - b) / m;
211
212 /* sort end-points' x and y components individually */
213 if (x1 < x2) {
214 xl = x1;
215 xh = x2;
216 } else {
217 xl = x2;
218 xh = x1;
219 }
220 if (y1 < y2) {
221 yl = y1;
222 yh = y2;
223 } else {
224 yl = y2;
225 yh = y1;
226 }
227
228 #define RISING(a, b, c) (((a)<=(b))&&((b)<=(c)))
229
230 /* check for a point that's entirely inside the rect */
231 if (RISING(rectx1, x1, rectx2) && RISING(recty1, y1, recty2)) {
232 x_result++;
233 y_result++;
234 intersection = SDL_TRUE;
235 } else /* it was determined earlier that *both* end-points are not contained */
236
237 if (RISING(rectx1, x2, rectx2) && RISING(recty1, y2, recty2)) {
238 **(x_result++) = x2;
239 **(y_result++) = y2;
240 intersection = SDL_TRUE;
241 }
242
243 if (RISING(recty1, left, recty2) && RISING(xl, rectx1, xh)) {
244 **(x_result++) = rectx1;
245 **(y_result++) = (int) left;
246 intersection = SDL_TRUE;
247 }
248
249 if (*x_result == NULL) return intersection;
250 if (RISING(recty1, right, recty2) && RISING(xl, rectx2, xh)) {
251 **(x_result++) = rectx2;
252 **(y_result++) = (int) right;
253 intersection = SDL_TRUE;
254 }
255
256 if (*x_result == NULL) return intersection;
257 if (RISING(rectx1, top, rectx2) && RISING(yl, recty1, yh)) {
258 **(x_result++) = (int) top;
259 **(y_result++) = recty1;
260 intersection = SDL_TRUE;
261 }
262
263 if (*x_result == NULL) return intersection;
264 if (RISING(rectx1, bottom, rectx2) && RISING(yl, recty2, yh)) {
265 **(x_result++) = (int) bottom;
266 **(y_result++) = recty2;
267 intersection = SDL_TRUE;
268 }
269
270 return intersection;
271 }
272
188 return SDL_FALSE; 273 return SDL_FALSE;
189 } 274 }
190 275
191 void 276 void
192 SDL_AddDirtyRect(SDL_DirtyRectList * list, const SDL_Rect * rect) 277 SDL_AddDirtyRect(SDL_DirtyRectList * list, const SDL_Rect * rect)