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Improved Circle Drawing Algorithm. #13

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Oct 14, 2020
Merged

Improved Circle Drawing Algorithm. #13

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01f06e4
Improved Cirle Draw Algorithm
scottbigbrain Oct 4, 2020
e55bc91
Added explanatory comments to New Circle Algorithm
scottbigbrain Oct 4, 2020
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82 changes: 39 additions & 43 deletions src/screen.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -159,58 +159,54 @@ end
sdl_colors(c::Colorant) = sdl_colors(convert(ARGB{Colors.FixedPointNumbers.Normed{UInt8,8}}, c))
sdl_colors(c::ARGB) = Int.(reinterpret.((red(c), green(c), blue(c), alpha(c))))

#Naive Algorithm, should be improved.
# improved circle drawing algorithm. slower but fills completely. needs optimization
function draw(s::Screen, circle::Circle, c::Colorant=colorant"black"; fill=false)
# define the center and needed sides of circle
centerX = Cint(circle.x)
centerY = Cint(circle.y)
int_rad = Cint(circle.r)
left = centerX - int_rad
top = centerY - int_rad

SDL2.SetRenderDrawColor(
s.renderer,
sdl_colors(c)...,
)
diameter = Cint(round(circle.r * 2));

centreX = Cint(round(circle.x))
centreY = Cint(round(circle.y))

x = Cint(round(circle.r - 1))
y = Cint(0)
tx = Cint(1)
ty = Cint(1)
error = (tx - diameter)

while (x >= y)
#Each of the following renders an eight of the circle
if !fill
SDL2.RenderDrawPoint(s.renderer, centreX + x, centreY - y);
SDL2.RenderDrawPoint(s.renderer, centreX + x, centreY + y);
SDL2.RenderDrawPoint(s.renderer, centreX - x, centreY - y);
SDL2.RenderDrawPoint(s.renderer, centreX - x, centreY + y);
SDL2.RenderDrawPoint(s.renderer, centreX + y, centreY - x);
SDL2.RenderDrawPoint(s.renderer, centreX + y, centreY + x);
SDL2.RenderDrawPoint(s.renderer, centreX - y, centreY - x);
SDL2.RenderDrawPoint(s.renderer, centreX - y, centreY + x);
else
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX + x, centreY - y);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX + x, centreY + y);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX - x, centreY - y);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX - x, centreY + y);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX + y, centreY - x);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX + y, centreY + x);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX - y, centreY - x);
SDL2.RenderDrawLine(s.renderer, centreX, centreY, centreX - y, centreY + x);
end

if (error <= 0)
y += Cint(1)
error += ty
ty += Cint(2)
end
# we consider a grid with sides equal to the circle's diameter
for x in left:centerX
for y in top:centerY

# for each pixel in the top left quadrant of the grid we measure the distance from the center.
dist = sqrt( (centerX - x)^2 + (centerY - y)^2 )

# if it is close to the circle's radius it and all associated points in the other quadrants are colored in.
if (dist <= circle.r + 0.5 && dist >= circle.r - 0.5)
rel_x = centerX - x
rel_y = centerY - y

quad1 = (x , y )
quad2 = (centerX + rel_x, y )
quad3 = (x , centerY + rel_y)
quad4 = (quad2[1] , quad3[2] )

SDL2.RenderDrawPoint(s.renderer, quad1[1], quad1[2])
SDL2.RenderDrawPoint(s.renderer, quad2[1], quad2[2])
SDL2.RenderDrawPoint(s.renderer, quad3[1], quad3[2])
SDL2.RenderDrawPoint(s.renderer, quad4[1], quad4[2])

# if we are told to fill in the circle we draw lines between all of the quadrants to completely fill the circle
if (fill == true)
SDL2.RenderDrawLine(s.renderer, quad1[1], quad1[2], quad2[1], quad2[2])
SDL2.RenderDrawLine(s.renderer, quad2[1], quad2[2], quad4[1], quad4[2])
SDL2.RenderDrawLine(s.renderer, quad4[1], quad4[2], quad3[1], quad3[2])
SDL2.RenderDrawLine(s.renderer, quad3[1], quad3[2], quad1[1], quad1[2])
end
end

if (error > 0)
x -= Cint(1)
tx += Cint(2)
error += (tx - diameter)
end
end
end

end

rect(x::Rect) = x
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