Ardour  9.0-pre0-582-g084a23a80d
gdkpoly-generic.h
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1 /* $TOG: poly.h /main/5 1998/02/06 17:47:27 kaleb $ */
2 /************************************************************************
3 
4 Copyright 1987, 1998 The Open Group
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22 
23 Copyright 1987 by Digital Equipment Corporation, Maynard, Massachusetts.
24 
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43 ************************************************************************/
44 
45 /*
46  * This file contains a few macros to help track
47  * the edge of a filled object. The object is assumed
48  * to be filled in scanline order, and thus the
49  * algorithm used is an extension of Bresenham's line
50  * drawing algorithm which assumes that y is always the
51  * major axis.
52  * Since these pieces of code are the same for any filled shape,
53  * it is more convenient to gather the library in one
54  * place, but since these pieces of code are also in
55  * the inner loops of output primitives, procedure call
56  * overhead is out of the question.
57  * See the author for a derivation if needed.
58  */
59 ␌
60 
61 /*
62  * In scan converting polygons, we want to choose those pixels
63  * which are inside the polygon. Thus, we add .5 to the starting
64  * x coordinate for both left and right edges. Now we choose the
65  * first pixel which is inside the pgon for the left edge and the
66  * first pixel which is outside the pgon for the right edge.
67  * Draw the left pixel, but not the right.
68  *
69  * How to add .5 to the starting x coordinate:
70  * If the edge is moving to the right, then subtract dy from the
71  * error term from the general form of the algorithm.
72  * If the edge is moving to the left, then add dy to the error term.
73  *
74  * The reason for the difference between edges moving to the left
75  * and edges moving to the right is simple: If an edge is moving
76  * to the right, then we want the algorithm to flip immediately.
77  * If it is moving to the left, then we don't want it to flip until
78  * we traverse an entire pixel.
79  */
80 #define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
81  int dx; /* local storage */ \
82 \
83  /* \
84  * if the edge is horizontal, then it is ignored \
85  * and assumed not to be processed. Otherwise, do this stuff. \
86  */ \
87  if ((dy) != 0) { \
88  xStart = (x1); \
89  dx = (x2) - xStart; \
90  if (dx < 0) { \
91  m = dx / (dy); \
92  m1 = m - 1; \
93  incr1 = -2 * dx + 2 * (dy) * m1; \
94  incr2 = -2 * dx + 2 * (dy) * m; \
95  d = 2 * m * (dy) - 2 * dx - 2 * (dy); \
96  } else { \
97  m = dx / (dy); \
98  m1 = m + 1; \
99  incr1 = 2 * dx - 2 * (dy) * m1; \
100  incr2 = 2 * dx - 2 * (dy) * m; \
101  d = -2 * m * (dy) + 2 * dx; \
102  } \
103  } \
104 }
105 ␌
106 #define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
107  if (m1 > 0) { \
108  if (d > 0) { \
109  minval += m1; \
110  d += incr1; \
111  } \
112  else { \
113  minval += m; \
114  d += incr2; \
115  } \
116  } else {\
117  if (d >= 0) { \
118  minval += m1; \
119  d += incr1; \
120  } \
121  else { \
122  minval += m; \
123  d += incr2; \
124  } \
125  } \
126 }
127 
128 ␌
129 /*
130  * This structure contains all of the information needed
131  * to run the bresenham algorithm.
132  * The variables may be hardcoded into the declarations
133  * instead of using this structure to make use of
134  * register declarations.
135  */
136 typedef struct {
137  int minor_axis; /* minor axis */
138  int d; /* decision variable */
139  int m, m1; /* slope and slope+1 */
140  int incr1, incr2; /* error increments */
142 
143 
144 #define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
145  BRESINITPGON(dmaj, min1, min2, bres.minor_axis, bres.d, \
146  bres.m, bres.m1, bres.incr1, bres.incr2)
147 
148 #define BRESINCRPGONSTRUCT(bres) \
149  BRESINCRPGON(bres.d, bres.minor_axis, bres.m, bres.m1, bres.incr1, bres.incr2)
150 
151 
152 
153 /*
154  * These are the data structures needed to scan
155  * convert regions. Two different scan conversion
156  * methods are available -- the even-odd method, and
157  * the winding number method.
158  * The even-odd rule states that a point is inside
159  * the polygon if a ray drawn from that point in any
160  * direction will pass through an odd number of
161  * path segments.
162  * By the winding number rule, a point is decided
163  * to be inside the polygon if a ray drawn from that
164  * point in any direction passes through a different
165  * number of clockwise and counter-clockwise path
166  * segments.
167  *
168  * These data structures are adapted somewhat from
169  * the algorithm in (Foley/Van Dam) for scan converting
170  * polygons.
171  * The basic algorithm is to start at the top (smallest y)
172  * of the polygon, stepping down to the bottom of
173  * the polygon by incrementing the y coordinate. We
174  * keep a list of edges which the current scanline crosses,
175  * sorted by x. This list is called the Active Edge Table (AET)
176  * As we change the y-coordinate, we update each entry in
177  * in the active edge table to reflect the edges new xcoord.
178  * This list must be sorted at each scanline in case
179  * two edges intersect.
180  * We also keep a data structure known as the Edge Table (ET),
181  * which keeps track of all the edges which the current
182  * scanline has not yet reached. The ET is basically a
183  * list of ScanLineList structures containing a list of
184  * edges which are entered at a given scanline. There is one
185  * ScanLineList per scanline at which an edge is entered.
186  * When we enter a new edge, we move it from the ET to the AET.
187  *
188  * From the AET, we can implement the even-odd rule as in
189  * (Foley/Van Dam).
190  * The winding number rule is a little trickier. We also
191  * keep the EdgeTableEntries in the AET linked by the
192  * nextWETE (winding EdgeTableEntry) link. This allows
193  * the edges to be linked just as before for updating
194  * purposes, but only uses the edges linked by the nextWETE
195  * link as edges representing spans of the polygon to
196  * drawn (as with the even-odd rule).
197  */
198 
199 /*
200  * for the winding number rule
201  */
202 #define CLOCKWISE 1
203 #define COUNTERCLOCKWISE -1
204 
205 typedef struct _EdgeTableEntry {
206  int ymax; /* ycoord at which we exit this edge. */
207  BRESINFO bres; /* Bresenham info to run the edge */
208  struct _EdgeTableEntry *next; /* next in the list */
209  struct _EdgeTableEntry *back; /* for insertion sort */
210  struct _EdgeTableEntry *nextWETE; /* for winding num rule */
211  int ClockWise; /* flag for winding number rule */
213 
214 
215 typedef struct _ScanLineList{
216  int scanline; /* the scanline represented */
217  EdgeTableEntry *edgelist; /* header node */
218  struct _ScanLineList *next; /* next in the list */
220 
221 
222 typedef struct {
223  int ymax; /* ymax for the polygon */
224  int ymin; /* ymin for the polygon */
225  ScanLineList scanlines; /* header node */
226 } EdgeTable;
227 
228 
229 /*
230  * Here is a struct to help with storage allocation
231  * so we can allocate a big chunk at a time, and then take
232  * pieces from this heap when we need to.
233  */
234 #define SLLSPERBLOCK 25
235 
236 typedef struct _ScanLineListBlock {
238  struct _ScanLineListBlock *next;
240 
241 
242 ␌
243 /*
244  *
245  * a few macros for the inner loops of the fill code where
246  * performance considerations don't allow a procedure call.
247  *
248  * Evaluate the given edge at the given scanline.
249  * If the edge has expired, then we leave it and fix up
250  * the active edge table; otherwise, we increment the
251  * x value to be ready for the next scanline.
252  * The winding number rule is in effect, so we must notify
253  * the caller when the edge has been removed so he
254  * can reorder the Winding Active Edge Table.
255  */
256 #define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) { \
257  if (pAET->ymax == y) { /* leaving this edge */ \
258  pPrevAET->next = pAET->next; \
259  pAET = pPrevAET->next; \
260  fixWAET = 1; \
261  if (pAET) \
262  pAET->back = pPrevAET; \
263  } \
264  else { \
265  BRESINCRPGONSTRUCT(pAET->bres); \
266  pPrevAET = pAET; \
267  pAET = pAET->next; \
268  } \
269 }
270 
271 
272 /*
273  * Evaluate the given edge at the given scanline.
274  * If the edge has expired, then we leave it and fix up
275  * the active edge table; otherwise, we increment the
276  * x value to be ready for the next scanline.
277  * The even-odd rule is in effect.
278  */
279 #define EVALUATEEDGEEVENODD(pAET, pPrevAET, y) { \
280  if (pAET->ymax == y) { /* leaving this edge */ \
281  pPrevAET->next = pAET->next; \
282  pAET = pPrevAET->next; \
283  if (pAET) \
284  pAET->back = pPrevAET; \
285  } \
286  else { \
287  BRESINCRPGONSTRUCT(pAET->bres); \
288  pPrevAET = pAET; \
289  pAET = pAET->next; \
290  } \
291 }
struct _EdgeTableEntry EdgeTableEntry
struct _ScanLineListBlock ScanLineListBlock
struct _ScanLineList ScanLineList
#define SLLSPERBLOCK
struct _EdgeTableEntry * next
struct _EdgeTableEntry * back
struct _EdgeTableEntry * nextWETE
ScanLineList SLLs[25]
struct _ScanLineListBlock * next
EdgeTableEntry * edgelist
struct _ScanLineList * next