Making a circle with lua?

Hi,
So today I was trying to make a circle in CC.
I googled a bit and understood, I had to use math.cos and math.sin.
Well I'm still lost :P/>
If someone could explain me, that would be awsome!

Thanks!

I'm not sure how it's done, but I know it has something to do with the pythagorean thereom, so yes you will need math.cos and math.sin probably somewhere in there.

I'm not entirely sure…

--# sX = x position, sY = y position, sR = radius
function circle(sX,sY,sR)

  local radius = math.pi * sR
  for i = 1, 360 do
    local x = math.sin(radius*i)
    local y = math.cos(radius*i)
    term.setCursorPos(sX+x,sY+y)
    term.write(" ")
  end

end

Maybe it's wrong, idk

Do you mean "draw a circle on the screen" or "make a turtle move around in a circle"? Are you talking about a basic circle, or a filled in circle?

basic, filled or not filled.

I'd be interested in seeing how this is done.. might make some sort of API if i can figure it out… Still a bit of a Lua noob though.

What you are looking for is the Midpoint circle algorithm, making voxel circles requires a bit of math. I might give it a try tho, since I have been slacking on my math usage lately.

Here's a very simple hollow circle function i just made for my own program, with the program specific parts stripped and some comments added. This can draw ellipsoids aswell.

function circleRender(x1,x2,y1,y2,color)
  if not (x1 and x2 and y1 and y2) then
    return
  end
  local x = {
    max = math.max(x1,x2), --right most x
    min = math.min(x1,x2) --left most x
  }
  x.rad = math.floor(x.max-x.min)/2 --radius
  x.center = x.rad+x.min --circle x-axis center
  local y = {
    max = math.max(y1,y2), --bottom y
    min = math.min(y1,y2) --top y
  }
  y.rad = (y.max-y.min)/2
  y.center = y.rad+y.min --circle y-axis center
  local thetha = 0
  local tPoints = {}
  while thetha <= 360 do
    local xP = math.floor(x.center+x.rad*math.cos(thetha)) --calculate x point
    local yP = math.floor(y.center+y.rad*math.sin(thetha)) --calculate y point
    tPoints[xP] = tPoints[xP] or {} --countine existing x-axis or create new one
    tPoints[xP][yP] = true -- mark point on y axis along x axis
    thetha = thetha+1
  end
  for x,yT in pairs(tPoints) do
    for y in pairs(yT) do
	  if y <= canvasEdge then
	    paintutils.drawPixel(x,y,color)
	  end
    end
  end
end

here's one I've thrown together in the past (slightly different version is also in my thread)

function drawCircle( centerX, centerY, radius, color )
	local isAdvanced = term.isColor and term.isColor()
	local char = isAdvanced and " " or "|"
	if isAdvanced then term.setBackgroundColor( color ) end
	local radStep = 1/(1.5*radius)
	for angle = 1, math.pi+radStep, radStep do
		local pX = math.cos( angle ) * radius * 1.5
		local pY = math.sin( angle ) * radius

		for i=-1,1,2 do
			for j=-1,1,2 do
				term.setCursorPos( centerX + i*pX, centerY + j*pY )
				write( char )
			end
		end
	end
end

it also supports non-advanced computers by having a char that it can print instead of colours.

theoriginalbit, on 09 March 2014 - 01:03 AM said:

here's one I've thrown together in the past (slightly different version is also in my thread)

function drawCircle( centerX, centerY, radius, color )
	local isAdvanced = term.isColor and term.isColor()
	local char = isAdvanced and " " or "|"
	if isAdvanced then term.setBackgroundColor( color ) end
	local radStep = 1/(1.5*radius)
	for angle = 1, math.pi+radStep, radStep do
		local pX = math.cos( angle ) * radius * 1.5
		local pY = math.sin( angle ) * radius

		for i=-1,1,2 do
			for j=-1,1,2 do
				term.setCursorPos( centerX + i*pX, centerY + j*pY )
				write( char )
			end
		end
	end
end

it also supports non-advanced computers by having a char that it can print instead of colours.

do you mind if I use this in my engine?

Hint: Search for "how to rasterize a circle" to get more useful hints on writing a program on how to do this. This is an 2D rasterizing problem that's well explored.

If you are drawing a hollow circle, the methods given above will work. If you want a filled circle, then it's best to think of this problem as drawing a series of horizontal lines instead of individual pixels.

If you are drawing circles and not ellipses, you can mirror the top and bottom halves of the circle.