1/************************************************************************ 2 3Copyright 1987, 1998 The Open Group 4 5Permission to use, copy, modify, distribute, and sell this software and its 6documentation for any purpose is hereby granted without fee, provided that 7the above copyright notice appear in all copies and that both that 8copyright notice and this permission notice appear in supporting 9documentation. 10 11The above copyright notice and this permission notice shall be included in 12all copies or substantial portions of the Software. 13 14THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 15IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 16FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 17OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN 18AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN 19CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. 20 21Except as contained in this notice, the name of The Open Group shall not be 22used in advertising or otherwise to promote the sale, use or other dealings 23in this Software without prior written authorization from The Open Group. 24 25 26Copyright 1987 by Digital Equipment Corporation, Maynard, Massachusetts. 27 28 All Rights Reserved 29 30Permission to use, copy, modify, and distribute this software and its 31documentation for any purpose and without fee is hereby granted, 32provided that the above copyright notice appear in all copies and that 33both that copyright notice and this permission notice appear in 34supporting documentation, and that the name of Digital not be 35used in advertising or publicity pertaining to distribution of the 36software without specific, written prior permission. 37 38DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 39ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL 40DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR 41ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, 42WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, 43ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS 44SOFTWARE. 45 46************************************************************************/ 47 48/* 49 * This file contains a few macros to help track 50 * the edge of a filled object. The object is assumed 51 * to be filled in scanline order, and thus the 52 * algorithm used is an extension of Bresenham's line 53 * drawing algorithm which assumes that y is always the 54 * major axis. 55 * Since these pieces of code are the same for any filled shape, 56 * it is more convenient to gather the library in one 57 * place, but since these pieces of code are also in 58 * the inner loops of output primitives, procedure call 59 * overhead is out of the question. 60 * See the author for a derivation if needed. 61 */ 62 63 64/* 65 * In scan converting polygons, we want to choose those pixels 66 * which are inside the polygon. Thus, we add .5 to the starting 67 * x coordinate for both left and right edges. Now we choose the 68 * first pixel which is inside the pgon for the left edge and the 69 * first pixel which is outside the pgon for the right edge. 70 * Draw the left pixel, but not the right. 71 * 72 * How to add .5 to the starting x coordinate: 73 * If the edge is moving to the right, then subtract dy from the 74 * error term from the general form of the algorithm. 75 * If the edge is moving to the left, then add dy to the error term. 76 * 77 * The reason for the difference between edges moving to the left 78 * and edges moving to the right is simple: If an edge is moving 79 * to the right, then we want the algorithm to flip immediately. 80 * If it is moving to the left, then we don't want it to flip until 81 * we traverse an entire pixel. 82 */ 83#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) do { \ 84 int dx; /* local storage */ \ 85\ 86 /* \ 87 * if the edge is horizontal, then it is ignored \ 88 * and assumed not to be processed. Otherwise, do this stuff. \ 89 */ \ 90 if ((dy) != 0) { \ 91 xStart = (x1); \ 92 dx = (x2) - xStart; \ 93 if (dx < 0) { \ 94 m = dx / (dy); \ 95 m1 = m - 1; \ 96 incr1 = -2 * dx + 2 * (dy) * m1; \ 97 incr2 = -2 * dx + 2 * (dy) * m; \ 98 d = 2 * m * (dy) - 2 * dx - 2 * (dy); \ 99 } else { \ 100 m = dx / (dy); \ 101 m1 = m + 1; \ 102 incr1 = 2 * dx - 2 * (dy) * m1; \ 103 incr2 = 2 * dx - 2 * (dy) * m; \ 104 d = -2 * m * (dy) + 2 * dx; \ 105 } \ 106 } \ 107} while (0) 108 109#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) do { \ 110 if (m1 > 0) { \ 111 if (d > 0) { \ 112 minval += m1; \ 113 d += incr1; \ 114 } \ 115 else { \ 116 minval += m; \ 117 d += incr2; \ 118 } \ 119 } else {\ 120 if (d >= 0) { \ 121 minval += m1; \ 122 d += incr1; \ 123 } \ 124 else { \ 125 minval += m; \ 126 d += incr2; \ 127 } \ 128 } \ 129} while (0) 130 131 132/* 133 * This structure contains all of the information needed 134 * to run the bresenham algorithm. 135 * The variables may be hardcoded into the declarations 136 * instead of using this structure to make use of 137 * register declarations. 138 */ 139typedef struct { 140 int minor_axis; /* minor axis */ 141 int d; /* decision variable */ 142 int m, m1; /* slope and slope+1 */ 143 int incr1, incr2; /* error increments */ 144} BRESINFO; 145 146 147#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \ 148 BRESINITPGON(dmaj, min1, min2, bres.minor_axis, bres.d, \ 149 bres.m, bres.m1, bres.incr1, bres.incr2) 150 151#define BRESINCRPGONSTRUCT(bres) \ 152 BRESINCRPGON(bres.d, bres.minor_axis, bres.m, bres.m1, bres.incr1, bres.incr2) 153 154 155 156/* 157 * These are the data structures needed to scan 158 * convert regions. Two different scan conversion 159 * methods are available -- the even-odd method, and 160 * the winding number method. 161 * The even-odd rule states that a point is inside 162 * the polygon if a ray drawn from that point in any 163 * direction will pass through an odd number of 164 * path segments. 165 * By the winding number rule, a point is decided 166 * to be inside the polygon if a ray drawn from that 167 * point in any direction passes through a different 168 * number of clockwise and counter-clockwise path 169 * segments. 170 * 171 * These data structures are adapted somewhat from 172 * the algorithm in (Foley/Van Dam) for scan converting 173 * polygons. 174 * The basic algorithm is to start at the top (smallest y) 175 * of the polygon, stepping down to the bottom of 176 * the polygon by incrementing the y coordinate. We 177 * keep a list of edges which the current scanline crosses, 178 * sorted by x. This list is called the Active Edge Table (AET) 179 * As we change the y-coordinate, we update each entry in 180 * in the active edge table to reflect the edges new xcoord. 181 * This list must be sorted at each scanline in case 182 * two edges intersect. 183 * We also keep a data structure known as the Edge Table (ET), 184 * which keeps track of all the edges which the current 185 * scanline has not yet reached. The ET is basically a 186 * list of ScanLineList structures containing a list of 187 * edges which are entered at a given scanline. There is one 188 * ScanLineList per scanline at which an edge is entered. 189 * When we enter a new edge, we move it from the ET to the AET. 190 * 191 * From the AET, we can implement the even-odd rule as in 192 * (Foley/Van Dam). 193 * The winding number rule is a little trickier. We also 194 * keep the EdgeTableEntries in the AET linked by the 195 * nextWETE (winding EdgeTableEntry) link. This allows 196 * the edges to be linked just as before for updating 197 * purposes, but only uses the edges linked by the nextWETE 198 * link as edges representing spans of the polygon to 199 * drawn (as with the even-odd rule). 200 */ 201 202/* 203 * for the winding number rule 204 */ 205#define CLOCKWISE 1 206#define COUNTERCLOCKWISE -1 207 208typedef struct _EdgeTableEntry { 209 int ymax; /* ycoord at which we exit this edge. */ 210 BRESINFO bres; /* Bresenham info to run the edge */ 211 struct _EdgeTableEntry *next; /* next in the list */ 212 struct _EdgeTableEntry *back; /* for insertion sort */ 213 struct _EdgeTableEntry *nextWETE; /* for winding num rule */ 214 int ClockWise; /* flag for winding number rule */ 215} EdgeTableEntry; 216 217 218typedef struct _ScanLineList{ 219 int scanline; /* the scanline represented */ 220 EdgeTableEntry *edgelist; /* header node */ 221 struct _ScanLineList *next; /* next in the list */ 222} ScanLineList; 223 224 225typedef struct { 226 int ymax; /* ymax for the polygon */ 227 int ymin; /* ymin for the polygon */ 228 ScanLineList scanlines; /* header node */ 229} EdgeTable; 230 231 232/* 233 * Here is a struct to help with storage allocation 234 * so we can allocate a big chunk at a time, and then take 235 * pieces from this heap when we need to. 236 */ 237#define SLLSPERBLOCK 25 238 239typedef struct _ScanLineListBlock { 240 ScanLineList SLLs[SLLSPERBLOCK]; 241 struct _ScanLineListBlock *next; 242} ScanLineListBlock; 243 244 245 246/* 247 * 248 * a few macros for the inner loops of the fill code where 249 * performance considerations don't allow a procedure call. 250 * 251 * Evaluate the given edge at the given scanline. 252 * If the edge has expired, then we leave it and fix up 253 * the active edge table; otherwise, we increment the 254 * x value to be ready for the next scanline. 255 * The winding number rule is in effect, so we must notify 256 * the caller when the edge has been removed so he 257 * can reorder the Winding Active Edge Table. 258 */ 259#define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) do { \ 260 if (pAET->ymax == y) { /* leaving this edge */ \ 261 pPrevAET->next = pAET->next; \ 262 pAET = pPrevAET->next; \ 263 fixWAET = 1; \ 264 if (pAET) \ 265 pAET->back = pPrevAET; \ 266 } \ 267 else { \ 268 BRESINCRPGONSTRUCT(pAET->bres); \ 269 pPrevAET = pAET; \ 270 pAET = pAET->next; \ 271 } \ 272} while (0) 273 274 275/* 276 * Evaluate the given edge at the given scanline. 277 * If the edge has expired, then we leave it and fix up 278 * the active edge table; otherwise, we increment the 279 * x value to be ready for the next scanline. 280 * The even-odd rule is in effect. 281 */ 282#define EVALUATEEDGEEVENODD(pAET, pPrevAET, y) do { \ 283 if (pAET->ymax == y) { /* leaving this edge */ \ 284 pPrevAET->next = pAET->next; \ 285 pAET = pPrevAET->next; \ 286 if (pAET) \ 287 pAET->back = pPrevAET; \ 288 } \ 289 else { \ 290 BRESINCRPGONSTRUCT(pAET->bres); \ 291 pPrevAET = pAET; \ 292 pAET = pAET->next; \ 293 } \ 294} while (0) 295