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a fencepost error

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This commit is contained in:
Amy Bowersox 2019-12-10 14:51:53 -07:00
parent ab16513e3a
commit cfc7519727
1 changed files with 7 additions and 5 deletions
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12
src/devctxt.c
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@ -19,7 +19,9 @@ inline static BYTE line_clip_outcode(INT32 x, INT32 y, INT32 xmin, INT32 ymin, I
return rc;
}
#define CPX 8 /* clipping precision in bits */
#define CPX 4 /* clipping precision in bits */
#define ONE (1 << CPX) /* constant for mathematics */
/* these macros keep the number of bits straight when doing fixed-point multiply & divide */
#define M(a, b) ((((a) * (b))) >> CPX)
@ -74,16 +76,16 @@ static BOOL line_clip(PINT32 output, INT32 x1, INT32 y1, INT32 x2, INT32 y2, INT
}
else if (outcode1 & 0x4)
{
tmp = M(x2 - x1, D(ymax - y1, y2 - y1));
tmp = M(x2 - x1, D(ymax - ONE - y1, y2 - y1));
x1 += tmp;
y1 = ymax;
y1 = ymax - ONE;
Log(LDEBUG, "clipped against bottom to point (%d, %d), dx=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
}
else if (outcode1 & 0x2)
{
tmp = M(y2 - y1, D(xmax - x1, x2 - x1));
tmp = M(y2 - y1, D(xmax - ONE - x1, x2 - x1));
y1 += tmp;
x1 = xmax;
x1 = xmax - ONE;
Log(LDEBUG, "clipped against right to point (%d, %d), dy=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
}
else if (outcode1 & 0x1)