Gabriele Cosmo
262 lines
8.7 KiB
Plaintext
262 lines
8.7 KiB
Plaintext
// Copyright (C) 2010, Guy Barrand. All rights reserved.
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// See the file tools.license for terms.
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#ifndef tools_zb_line
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#define tools_zb_line
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/* from X/poly.h */
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/*
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* This file contains a few macros to help track
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* the edge of a filled object. The object is assumed
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* to be filled in scanline order, and thus the
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* algorithm used is an extension of Bresenham's line
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* drawing algorithm which assumes that y is always the
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* major axis.
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* Since these pieces of code are the same for any filled shape,
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* it is more convenient to gather the library in one
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* place, but since these pieces of code are also in
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* the inner loops of output primitives, procedure call
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* overhead is out of the question.
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* See the author for a derivation if needed.
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*/
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/*
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* In scan converting polygons, we want to choose those pixels
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* which are inside the polygon. Thus, we add .5 to the starting
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* x coordinate for both left and right edges. Now we choose the
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* first pixel which is inside the pgon for the left edge and the
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* first pixel which is outside the pgon for the right edge.
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* Draw the left pixel, but not the right.
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*
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* How to add .5 to the starting x coordinate:
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* If the edge is moving to the right, then subtract dy from the
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* error term from the general form of the algorithm.
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* If the edge is moving to the left, then add dy to the error term.
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*
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* The reason for the difference between edges moving to the left
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* and edges moving to the right is simple: If an edge is moving
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* to the right, then we want the algorithm to flip immediately.
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* If it is moving to the left, then we don't want it to flip until
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* we traverse an entire pixel.
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*/
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#define LARGE_COORDINATE 1000000
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#define SMALL_COORDINATE -LARGE_COORDINATE
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#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
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int dx; /* local storage */ \
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\
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/* \
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* if the edge is horizontal, then it is ignored \
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* and assumed not to be processed. Otherwise, do this stuff. \
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*/ \
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if ((dy) != 0) { \
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xStart = (x1); \
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dx = (x2) - xStart; \
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if (dx < 0) { \
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m = dx / (dy); \
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m1 = m - 1; \
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incr1 = -2 * dx + 2 * (dy) * m1; \
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incr2 = -2 * dx + 2 * (dy) * m; \
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d = 2 * m * (dy) - 2 * dx - 2 * (dy); \
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} else { \
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m = dx / (dy); \
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m1 = m + 1; \
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incr1 = 2 * dx - 2 * (dy) * m1; \
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incr2 = 2 * dx - 2 * (dy) * m; \
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d = -2 * m * (dy) + 2 * dx; \
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} \
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} \
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}
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#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
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if (m1 > 0) { \
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if (d > 0) { \
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minval += m1; \
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d += incr1; \
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} \
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else { \
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minval += m; \
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d += incr2; \
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} \
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} else {\
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if (d >= 0) { \
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minval += m1; \
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d += incr1; \
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} \
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else { \
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minval += m; \
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d += incr2; \
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} \
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} \
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}
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/*
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* This structure contains all of the information needed
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* to run the bresenham algorithm.
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* The variables may be hardcoded into the declarations
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* instead of using this structure to make use of
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* register declarations.
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*/
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typedef struct {
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int minor_axis; /* minor axis */
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int d; /* decision variable */
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int m, m1; /* slope and slope+1 */
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int incr1, incr2; /* error increments */
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} BRESINFO;
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#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
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BRESINITPGON(dmaj, min1, min2, bres.minor_axis, bres.d, \
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bres.m, bres.m1, bres.incr1, bres.incr2)
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#define BRESINCRPGONSTRUCT(bres) \
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BRESINCRPGON(bres.d, bres.minor_axis, bres.m, bres.m1, bres.incr1, bres.incr2)
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/*
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* These are the data structures needed to scan
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* convert regions. Two different scan conversion
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* methods are available -- the even-odd method, and
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* the winding number method.
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* The even-odd rule states that a point is inside
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* the polygon if a ray drawn from that point in any
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* direction will pass through an odd number of
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* path segments.
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* By the winding number rule, a point is decided
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* to be inside the polygon if a ray drawn from that
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* point in any direction passes through a different
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* number of clockwise and counter-clockwise path
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* segments.
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*
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* These data structures are adapted somewhat from
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* the algorithm in (Foley/Van Dam) for scan converting
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* polygons.
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* The basic algorithm is to start at the top (smallest y)
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* of the polygon, stepping down to the bottom of
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* the polygon by incrementing the y coordinate. We
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* keep a list of edges which the current scanline crosses,
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* sorted by x. This list is called the Active Edge Table (AET)
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* As we change the y-coordinate, we update each entry in
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* in the active edge table to reflect the edges new xcoord.
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* This list must be sorted at each scanline in case
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* two edges intersect.
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* We also keep a data structure known as the Edge Table (ET),
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* which keeps track of all the edges which the current
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* scanline has not yet reached. The ET is basically a
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* list of ScanLineList structures containing a list of
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* edges which are entered at a given scanline. There is one
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* ScanLineList per scanline at which an edge is entered.
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* When we enter a new edge, we move it from the ET to the AET.
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*
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* From the AET, we can implement the even-odd rule as in
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* (Foley/Van Dam).
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* The winding number rule is a little trickier. We also
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* keep the EdgeTableEntries in the AET linked by the
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* nextWETE (winding EdgeTableEntry) link. This allows
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* the edges to be linked just as before for updating
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* purposes, but only uses the edges linked by the nextWETE
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* link as edges representing spans of the polygon to
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* drawn (as with the even-odd rule).
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*/
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/*
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* for the winding number rule
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*/
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//#define CLOCKWISE 1
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//#define COUNTERCLOCKWISE -1
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typedef struct _EdgeTableEntry {
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int ymax; /* ycoord at which we exit this edge. */
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BRESINFO bres; /* Bresenham info to run the edge */
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struct _EdgeTableEntry *next; /* next in the list */
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struct _EdgeTableEntry *back; /* for insertion sort */
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struct _EdgeTableEntry *nextWETE; /* for winding num rule */
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int ClockWise; /* flag for winding number rule */
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} EdgeTableEntry;
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typedef struct _ScanLineList{
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int scanline; /* the scanline represented */
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EdgeTableEntry *edgelist; /* header node */
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struct _ScanLineList *next; /* next in the list */
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} ScanLineList;
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typedef struct {
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int ymax; /* ymax for the polygon */
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int ymin; /* ymin for the polygon */
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ScanLineList scanlines; /* header node */
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} EdgeTable;
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/*
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* Here is a struct to help with storage allocation
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* so we can allocate a big chunk at a time, and then take
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* pieces from this heap when we need to.
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*/
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#define SLLSPERBLOCK 25
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typedef struct _ScanLineListBlock {
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ScanLineList SLLs[SLLSPERBLOCK];
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struct _ScanLineListBlock *next;
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} ScanLineListBlock;
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/*
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*
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* a few macros for the inner loops of the fill code where
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* performance considerations don't allow a procedure call.
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*
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* Evaluate the given edge at the given scanline.
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* If the edge has expired, then we leave it and fix up
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* the active edge table; otherwise, we increment the
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* x value to be ready for the next scanline.
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* The winding number rule is in effect, so we must notify
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* the caller when the edge has been removed so he
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* can reorder the Winding Active Edge Table.
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*/
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#define EVALUATEEDGEWINDING(pAET, pPrevAET, y, fixWAET) { \
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if (pAET->ymax == y) { /* leaving this edge */ \
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pPrevAET->next = pAET->next; \
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pAET = pPrevAET->next; \
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fixWAET = 1; \
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if (pAET) \
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pAET->back = pPrevAET; \
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} \
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else { \
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BRESINCRPGONSTRUCT(pAET->bres) \
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pPrevAET = pAET; \
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pAET = pAET->next; \
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} \
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}
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/*
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* Evaluate the given edge at the given scanline.
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* If the edge has expired, then we leave it and fix up
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* the active edge table; otherwise, we increment the
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* x value to be ready for the next scanline.
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* The even-odd rule is in effect.
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*/
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#define EVALUATEEDGEEVENODD(pAET, pPrevAET, y) { \
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if (pAET->ymax == y) { /* leaving this edge */ \
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pPrevAET->next = pAET->next; \
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pAET = pPrevAET->next; \
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if (pAET) \
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pAET->back = pPrevAET; \
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} \
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else { \
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BRESINCRPGONSTRUCT(pAET->bres) \
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pPrevAET = pAET; \
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pAET = pAET->next; \
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} \
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}
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#endif
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