Anonymous user
Talk:Xiaolin Wu's line algorithm: Difference between revisions
→Bug in the C code?: new section
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Any guy can give me '''Xiaolin Wu's line algorithm'''s code in C#.
Than you.
== Bug in the C code? ==
<lang c>
} else {
if ( y2 < y1 ) {
swap_(x1, x2);
swap_(y1, y2);
}
double gradient = dx / dy;
double yend = round_(y1);
double xend = x1 + gradient*(yend - y1);
double ygap = rfpart_(y1 + 0.5);
int ypxl1 = yend;
int xpxl1 = ipart_(xend);
plot_(xpxl1, ypxl1, rfpart_(xend)*ygap);
plot_(xpxl1, ypxl1+1, fpart_(xend)*ygap);
double interx = xend + gradient;
yend = round_(y2);
xend = x2 + gradient*(yend - y2);
ygap = fpart_(y2+0.5);
int ypxl2 = yend;
int xpxl2 = ipart_(xend);
plot_(xpxl2, ypxl2, rfpart_(xend) * ygap);
plot_(xpxl2, ypxl2 + 1, fpart_(xend) * ygap);
int y;
for(y=ypxl1+1; y <= (ypxl2-1); y++) {
plot_(ipart_(interx), y, rfpart_(interx));
plot_(ipart_(interx) + 1, y, fpart_(interx));
interx += gradient;
}
}
}
</lang>
The start and end pixels here in the else where fabs(dx) <= fabs(dy), should have a secondary plot point +1 in the x-direction, not y-direction. It's correct for the main loop and the first if, but not the two end points, for any drawn line with a slope greater or equal to 1.
So where it says:
<lang c>
plot_(xpxl2, ypxl2, rfpart_(xend) * ygap);
plot_(xpxl2, ypxl2 + 1, fpart_(xend) * ygap);
</lang>
it should say:
<lang c>
plot_(xpxl2, ypxl2, rfpart_(xend) * ygap);
plot_(xpxl2 + 1, ypxl2, fpart_(xend) * ygap);
</lang>
[[Special:Contributions/76.175.220.55|76.175.220.55]] 11:20, 3 July 2011 (UTC)
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