From: Sergio Masci (sergio@titan.demon.co.uk)
Date: Tue 01 Feb 2000 - 21:28:37 IST
Here's some code I knocked up to draw anti-aliased lines. I hope it helps.
It uses 32 bit fixed point arithmatic and only allows 8 levels of
brightness, but its really simple. I've also produced a simple picture
showing lines that are drawn with it as pairs of anti-aliased and
non-anti-aliased lines.
The original line drawing code was taken from IPAD and hacked to removed
IPAD dependentcies.
Sergio Masci
http://www.demon.co.uk/titan
for a simple test define colour_tbl as
int colour_tbl[] =
{
// standard VGA palette grey scale
30, 29, 28, 27, 26, 25, 24, 23, 22
};
/*----------------------------------------------------------------------*/
// colour_tbl should contain 9 entries corresponding to the
// brightnesses of the required colour in steps of 1/8 from 0 to 8
//
// colour_tbl[0] = colour * 8/8
// colour_tbl[1] = colour * 7/8
// colour_tbl[2] = colour * 6/8
// ...
// colour_tbl[7] = colour * 1/8
// colour_tbl[8] = colour * 0/8
/*----------------------------------------------------------------------*/
void draw_line(int x1, int y1, int x2, int y2, int colour_tbl[])
{
int j, cnt,
ixstep, iystep;
long fx1, fy1,
xstep, ystep;
int p1, p2;
dx = x2 - x1;
dy = y2 - y1;
ixstep = sign(dx);
iystep = sign(dy);
xstep = ixstep << 16;
ystep = iystep << 16;
if (abs(dx) <= abs(dy))
{
xstep = (dx << 16) / abs(dy);
}
else
{ ystep = (dy << 16) / abs(dx);
}
fx1 = x1 << 16;
fy1 = y1 << 16;
// include end point i.e. x2-x1+1 where cnt = x2-x1
cnt++;
>>>>>>
>>>>>> replace this section of code
>>>>>>
int colour = colour_tbl[0];
for (j=cnt; j>0; j--)
{
x1 = fx1 >> 16;
y1 = fy1 >> 16;
set_xpixel_colour(x1, y1, colour);
fx1 += xstep;
fy1 += ystep;
}
>>>>>>
>>>>>> with this
>>>>>>
if (abs(dx) <= abs(dy))
{
for (j=cnt; j>0; j--)
{
x1 = fx1 >> 16;
// fraction of pixel between x and x+1
// as n/8 and n1/8
p1 = (fx1 >> 13) & 7;
p2 = 9 - p1;
set_xpixel_colour(x1, y1, colour_tbl[p1]);
set_xpixel_colour(x1+1, y1, colour_tbl[p2]);
fx1 += xstep;
y1 += iystep;
}
}
else
{
for (j=cnt; j>0; j--)
{
y1 = fy1 >> 16;
// fraction of pixel between y and y+1
// as n/8 and n1/8
p1 = (fy1 >> 13) & 7;
p2 = 8 - p1;
set_xpixel_colour(x1, y1, colour_tbl[p1]);
set_xpixel_colour(x1, y1+1, colour_tbl[p2]);
x1 += ixstep;
fy1 += ystep;
}
}
}
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