/* $Id: poly.h,v 1.1.1.1 90/11/28 17:03:00 altenhof Exp $ */ /************************************************************************ Copyright 1987 by Digital Equipment Corporation, Maynard, Massachusetts, and the Massachusetts Institute of Technology, Cambridge, Massachusetts. All Rights Reserved Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the names of Digital or MIT not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. ************************************************************************/ #define NULL 0 /* * This file contains a few macros to help track the edge of a filled object. * The object is assumed to be filled in scanline order, and thus the * algorithm used is an extension of Bresenham's line drawing algorithm which * assumes that y is always the major axis. Since these pieces of code are * the same for any filled shape, it is more convenient to gather the library * in one place, but since these pieces of code are also in the inner loops * of output primitives, procedure call overhead is out of the question. See * the author for a derivation if needed. */ /* * In scan converting polygons, we want to choose those pixels which are * inside the polygon. Thus, we add .5 to the starting x coordinate for both * left and right edges. Now we choose the first pixel which is inside the * pgon for the left edge and the first pixel which is outside the pgon for * the right edge. Draw the left pixel, but not the right. * * How to add .5 to the starting x coordinate: If the edge is moving to the * right, then subtract dy from the error term from the general form of the * algorithm. If the edge is moving to the left, then add dy to the error * term. * * The reason for the difference between edges moving to the left and edges * moving to the right is simple: If an edge is moving to the right, then we * want the algorithm to flip immediately. If it is moving to the left, then * we don't want it to flip until we traverse an entire pixel. */ #define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \ int dx; /* local storage */ \ \ /* \ * if the edge is horizontal, then it is ignored \ * and assumed not to be processed. Otherwise, do this stuff. \ */ \ if ((dy) != 0) { \ xStart = (x1); \ dx = (x2) - xStart; \ if (dx < 0) { \ m = dx / (dy); \ m1 = m - 1; \ incr1 = -2 * dx + 2 * (dy) * m1; \ incr2 = -2 * dx + 2 * (dy) * m; \ d = 2 * m * (dy) - 2 * dx - 2 * (dy); \ } else { \ m = dx / (dy); \ m1 = m + 1; \ incr1 = 2 * dx - 2 * (dy) * m1; \ incr2 = 2 * dx - 2 * (dy) * m; \ d = -2 * m * (dy) + 2 * dx; \ } \ } \ } #define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \ if (m1 > 0) { \ if (d > 0) { \ minval += m1; \ d += incr1; \ } \ else { \ minval += m; \ d += incr2; \ } \ } else {\ if (d >= 0) { \ minval += m1; \ d += incr1; \ } \ else { \ minval += m; \ d += incr2; \ } \ } \ } /* * This structure contains all of the information needed to run the bresenham * algorithm. The variables may be hardcoded into the declarations instead of * using this structure to make use of register declarations. */ typedef struct { int minor_axis; /* minor axis */ int d; /* decision variable */ int m, m1; /* slope and slope+1 */ int incr1, incr2; /* error increments */ } BRESINFO; #define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \ BRESINITPGON(dmaj, min1, min2, bres.minor_axis, bres.d, \ bres.m, bres.m1, bres.incr1, bres.incr2) #define BRESINCRPGONSTRUCT(bres) \ BRESINCRPGON(bres.d, bres.minor_axis, bres.m, bres.m1, bres.incr1, bres.incr2) /* * These are the data structures needed to scan convert regions. Two * different scan conversion methods are available -- the even-odd method, * and the winding number method. The even-odd rule states that a point is * inside the polygon if a ray drawn from that point in any direction will * pass through an odd number of path segments. By the winding number rule, a * point is decided to be inside the polygon if a ray drawn from that point * in any direction passes through a different number of clockwise and * counter-clockwise path segments. * * These data structures are adapted somewhat from the algorithm in (Foley/Van * Dam) for scan converting polygons. The basic algorithm is to start at the * top (smallest y) of the polygon, stepping down to the bottom of the * polygon by incrementing the y coordinate. We keep a list of edges which * the current scanline crosses, sorted by x. This list is called the Active * Edge Table (AET) As we change the y-coordinate, we update each entry in in * the active edge table to reflect the edges new xcoord. This list must be * sorted at each scanline in case two edges intersect. We also keep a data * structure known as the Edge Table (ET), which keeps track of all the edges * which the current scanline has not yet reached. The ET is basically a * list of ScanLineList structures containing a list of edges which are * entered at a given scanline. There is one ScanLineList per scanline at * which an edge is entered. When we enter a new edge, we move it from the ET * to the AET. * * From the AET, we can implement the even-odd rule as in (Foley/Van Dam). The * winding number rule is a little trickier. We also keep the * EdgeTableEntries in the AET linked by the nextWETE (winding * EdgeTableEntry) link. This allows the edges to be linked just as before * for updating purposes, but only uses the edges linked by the nextWETE link * as edges representing spans of the polygon to drawn (as with the even-odd * rule). */ /* * for the winding number rule */ #define CLOCKWISE 1 #define COUNTERCLOCKWISE -1 typedef struct _EdgeTableEntry { int ymax; /* ycoord at which we exit this edge. */ BRESINFO bres; /* Bresenham info to run the edge */ struct _EdgeTableEntry *next; /* next in the list */ struct _EdgeTableEntry *back; /* for insertion sort */ struct _EdgeTableEntry *nextWETE; /* for winding num rule */ int ClockWise; /* flag for winding number rule */ } EdgeTableEntry; typedef struct _ScanLineList { int scanline; /* the scanline represented */ EdgeTableEntry *edgelist; /* header node */ struct _ScanLineList *next; /* next in the list */ } ScanLineList; typedef struct { int ymax; /* ymax for the polygon */ int ymin; /* ymin for the polygon */ ScanLineList scanlines; /* header node */ } EdgeTable; /* * Here is a struct to help with storage allocation so we can allocate a big * chunk at a time, and then take pieces from this heap when we need to. */ #define SLLSPERBLOCK 25 typedef struct _ScanLineListBlock { ScanLineList SLLs[SLLSPERBLOCK]; struct _ScanLineListBlock *next; } ScanLineListBlock; /* * a few macros for the inner loops of the fill code where performance * considerations don't allow a procedure call. * * Evaluate the given edge at the given scanline. If the edge has expired, then * we leave it and fix up the active edge table; otherwise, we increment the * x value to be ready for the next scanline. The winding number rule is in * effect, so we must notify the caller when the edge has been removed so he * can reorder the Winding Active Edge Table. */ #define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) { \ if (pAET->ymax == y) { /* leaving this edge */ \ pPrevAET->next = pAET->next; \ pAET = pPrevAET->next; \ fixWAET = 1; \ if (pAET) \ pAET->back = pPrevAET; \ } \ else { \ BRESINCRPGONSTRUCT(pAET->bres); \ pPrevAET = pAET; \ pAET = pAET->next; \ } \ } /* * Evaluate the given edge at the given scanline. If the edge has expired, * then we leave it and fix up the active edge table; otherwise, we increment * the x value to be ready for the next scanline. The even-odd rule is in * effect. */ #define EVALUATEEDGEEVENODD(pAET, pPrevAET, y) { \ if (pAET->ymax == y) { /* leaving this edge */ \ pPrevAET->next = pAET->next; \ pAET = pPrevAET->next; \ if (pAET) \ pAET->back = pPrevAET; \ } \ else { \ BRESINCRPGONSTRUCT(pAET->bres); \ pPrevAET = pAET; \ pAET = pAET->next; \ } \ }