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#ifndef SCANFILLINCLUDED
#define SCANFILLINCLUDED
/*
* miscanfill.h
*
* Written by Brian Kelleher; Jan 1985
*
* 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 polygon for the left edge and the
* first pixel which is outside the polygon 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)
#endif
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