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1.1 root 1: /* $Header: miscanfill.h,v 1.1 87/09/11 07:20:22 toddb Exp $ */
2: #ifndef SCANFILLINCLUDED
3: #define SCANFILLINCLUDED
4: /*
5: * scanfill.h
6: *
7: * Written by Brian Kelleher; Jan 1985
8: *
9: * This file contains a few macros to help track
10: * the edge of a filled object. The object is assumed
11: * to be filled in scanline order, and thus the
12: * algorithm used is an extension of Bresenham's line
13: * drawing algorithm which assumes that y is always the
14: * major axis.
15: * Since these pieces of code are the same for any filled shape,
16: * it is more convenient to gather the library in one
17: * place, but since these pieces of code are also in
18: * the inner loops of output primitives, procedure call
19: * overhead is out of the question.
20: * See the author for a derivation if needed.
21: */
22:
23:
24: /*
25: * In scan converting polygons, we want to choose those pixels
26: * which are inside the polygon. Thus, we add .5 to the starting
27: * x coordinate for both left and right edges. Now we choose the
28: * first pixel which is inside the pgon for the left edge and the
29: * first pixel which is outside the pgon for the right edge.
30: * Draw the left pixel, but not the right.
31: *
32: * How to add .5 to the starting x coordinate:
33: * If the edge is moving to the right, then subtract dy from the
34: * error term from the general form of the algorithm.
35: * If the edge is moving to the left, then add dy to the error term.
36: *
37: * The reason for the difference between edges moving to the left
38: * and edges moving to the right is simple: If an edge is moving
39: * to the right, then we want the algorithm to flip immediately.
40: * If it is moving to the left, then we don't want it to flip until
41: * we traverse an entire pixel.
42: */
43: #define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
44: int dx; /* local storage */ \
45: \
46: /* \
47: * if the edge is horizontal, then it is ignored \
48: * and assumed not to be processed. Otherwise, do this stuff. \
49: */ \
50: if ((dy) != 0) { \
51: xStart = (x1); \
52: dx = (x2) - xStart; \
53: if (dx < 0) { \
54: m = dx / (dy); \
55: m1 = m - 1; \
56: incr1 = -2 * dx + 2 * (dy) * m1; \
57: incr2 = -2 * dx + 2 * (dy) * m; \
58: d = 2 * m * (dy) - 2 * dx - 2 * (dy); \
59: } else { \
60: m = dx / (dy); \
61: m1 = m + 1; \
62: incr1 = 2 * dx - 2 * (dy) * m1; \
63: incr2 = 2 * dx - 2 * (dy) * m; \
64: d = -2 * m * (dy) + 2 * dx; \
65: } \
66: } \
67: }
68:
69: #define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
70: if (m1 > 0) { \
71: if (d > 0) { \
72: minval += m1; \
73: d += incr1; \
74: } \
75: else { \
76: minval += m; \
77: d += incr2; \
78: } \
79: } else {\
80: if (d >= 0) { \
81: minval += m1; \
82: d += incr1; \
83: } \
84: else { \
85: minval += m; \
86: d += incr2; \
87: } \
88: } \
89: }
90:
91:
92: /*
93: * This structure contains all of the information needed
94: * to run the bresenham algorithm.
95: * The variables may be hardcoded into the declarations
96: * instead of using this structure to make use of
97: * register declarations.
98: */
99: typedef struct {
100: int minor; /* minor axis */
101: int d; /* decision variable */
102: int m, m1; /* slope and slope+1 */
103: int incr1, incr2; /* error increments */
104: } BRESINFO;
105:
106:
107: #define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
108: BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \
109: bres.m, bres.m1, bres.incr1, bres.incr2)
110:
111: #define BRESINCRPGONSTRUCT(bres) \
112: BRESINCRPGON(bres.d, bres.minor, bres.m, bres.m1, bres.incr1, bres.incr2)
113:
114:
115: #endif SCANFILLINCLUDED
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