i would convert the 2 circles into 2 arrays of raster lines
(same as you would for drawing triangles).
each raster has:
x1, -left side of circle
x2, -right side of circle
y, -y coord of raster line
midx -intersection coord (to be calculated)
so you can draw an entire circle by stepping through the array.
for y= y1 to y2
draw_line (x1, y, x2, y, color);
NOTE: if you have an optimized draw_hline function,
this will be faster than a generic draw_line (for software rendering).
For opengl it might not matter.
1.
sort the circles so circle1 is on the left and circle2 on the right
2.
loop thru the raster array for each circle and calculate the intersection x-coord.
To get the even split down the middle, just average the overlapping
x coordinates.
do a bounding box check on the y coordinate first.
for each raster line (y coord) from circle1 that intersects circle2
then do bounds checking to determine if they intersect for x coordinates too
if (intersects)
midx= the average of circle1_x2 and circle2_x1
3. draw each circle by looping through the raster lines.
circle1:
for y= y1 to y2
draw_line (circle1_x1, y, midx-1, y, color)
circle2:
for y= y1 to y2
draw_line (midx, y, circle2_x2, y, color)
obviously, if both circles aren't on the same y coordinate u have to do
the relative y-coord math when comparing the raster lines.
This should work for circles of different sizes too, i think.
this algorithm probably only works as long as 1 circle is not completely inside
the other circle1. You'll have to do the math to prevent that case from happening.
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