1. Re: xor_line
Hawke wrote:
>>i've been goofing around with bresenham's circle algorithm...
>>it seems to miss a couple dots around the circle...
Ad Rienks wrote:
>I think I know the reason: look at the round() function
>you posted the other day.
> Hope this helps
well, heh, bresenham's algorithms don't use round...
but!, thanks for spotting a potential defect in round() :)
here is the adaptation of bresenham's circle
algorithm i've been playing with:
-------------begin code
procedure true_plot4(sequence cntr, integer x,
integer y, sequence clr)
--this is the 'negating' part of the algorithm
true_pixel( cntr + { x, y}, clr ) --behaves just like
true_pixel( cntr + { x,-y}, clr ) --pixel() in EU
true_pixel( cntr + {-x, y}, clr )
true_pixel( cntr + {-x,-y}, clr )
end procedure
global procedure true_circle(sequence cntr, integer rad, sequence clr)
--Bresenham's algorithm for circles, interpreted for truecolor
--with optimizations for speed
--based upon the premise that a circle is symmetric every 45
--degrees which means you only calculate 0..45 and plot the
--other 8 segments via x,y flipping and negating
--cntr=center, rad=radius, clr=BGR color value {B,G,R}
integer x,y,d,tmp
x = 0
y = rad
d = 3 - rad
d = d - rad
while y > x do
--Draw the 8 circle pixels
true_plot4( cntr, x, y, clr) --this is the flipping
true_plot4( cntr, y, x, clr) --part of the algorithm
if d < 0 then
--d = d + (4 * x) + 6
tmp = x * 4
d = d + tmp
d = d + 6
else
--d = d + 4 * (x - y) + 10
tmp = x - y
tmp = tmp * 4
d = d + tmp
d = d + 10
y = y - 1
end if
x = x + 1
end while
end procedure
-------------end code
when i do something like:
for r=1 to 50 do
--plot a bright green circle, near mid screen
true_circle({320,240},r,{100,200,100})
end for
well, it's like a filled, 100pixel diameter circle, but
there are 'spots' in it... now, if you don't wanna run
this code in truecolor, just change the 4 lines in
true_plot4, alter the arguments for color (clr) to
accept integers and test away...
*watches thinking caps begin to smolder*
--Hawke'
