Subj : Re: fill in a segment of a circle on a graph
To   : comp.programming
From : Willem
Date : Mon Sep 05 2005 05:22 pm

aiiadict@gmail.com wrote:
) hi,
)
) segment of circle = 45degree (constant) "pie slice"
) radius of circle = variable, and known
) angle = variable and known  (this the angle of line running through
) center of the pie slice, the slice extending 22.5 degrees to each side
) of this line)
)
)
) goal:
)
) 0,0 on a graph is the center of the circle
)
) input:
)
) 1)angle = 0 degrees for example, compass direction North
) 2)radius (30, for example)
)
) what coordinates would be included in this slice?
)
) I want the coordinates of all cells outlined by the circle segment.
)
) I could draw the arc, and the edges of the slice, and then use
) some sort of fill routine.  I thought perhaps someone here would
) know a neat algorithm.
)
) Bresenhams algorithm looks like it would work, but I haven't
) figured out the code yet.  Trying to get it to do any segment
) of an arc is taking me a while to figure out.

If you can draw the arc and the edges, you can do a walk around the edge.
You need a list a 'left' and a 'right' for each x line.
At every crossing of an x line, store the current y coordinate.
Then, at the end, walk the list and draw x lines from 'left' to 'right'.

(Yes that's a fill routine.)


Alternatively, you could iterate over all coordinates (within a bounding
box) and check them against the three simple equations for the three
bounding lines.  You can optimize this by making a skewed box that follows
the left side of the shape as closely as possible, and by stopping the
iteration of a scanline as soon as you jump from 'inside' to 'outside'.


Dunno which is faster.


SaSW, Willem
-- 
Disclaimer: I am in no way responsible for any of the statements
            made in the above text. For all I know I might be
            drugged or something..
            No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

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