DrawArcs

DrawArcs.lua

-- LOVE2D 0.9.0
-- main.lua

-- Left-click somewhere to add point
-- Left-click and drag green point to move it
-- Right-click green point to remove it
-- Left-click and drag red point to modify starting angle
-- Backspace to remove all points

local Vector2;Vector2 = {
	new = function(x,y)
		return setmetatable({x=tonumber(x) or 0,y=tonumber(y) or 0},Vector2.mt)
	end;
	mt = {
		__index = {
			magnitude = function(v) return math.sqrt(v.x^2 + v.y^2) end;
			unit = function(v) return Vector2.new(v.x/v:magnitude(),v.y/v:magnitude()) end;
			dot = function(a,b) return a.x*b.x + a.y*b.y end;
			perp = function(v) return Vector2.new(v.y,-v.x) end;
		};
		__eq = function(a,b)
			return a.x == b.x and a.y == b.y
		end;
		__add = function(a,b)
			return Vector2.new(a.x + b.x, a.y + b.y)
		end;
		__sub = function(a,b)
			return Vector2.new(a.x - b.x, a.y - b.y)
		end;
		__mul = function(a,b)
			if type(a) == 'number' then
				return Vector2.new(a*b.x, a*b.y)
			elseif type(b) == 'number' then
				return Vector2.new(a.x*b, a.y*b)
			else
				return Vector2.new(a.x*b.x, a.y*b.y)
			end
		end;
		__unm = function(v)
			return Vector2.new(-v.x,-v.y);
		end;
		__div = function(a,b)
			if type(a) == 'number' then
				return Vector2.new(a/b.x, a/b.y)
			elseif type(b) == 'number' then
				return Vector2.new(a.x/b, a.y/b)
			else
				return Vector2.new(a.x/b.x, a.y/b.y)
			end
		end;
		__tostring = function(object)
			return '[' .. object.x .. ', ' .. object.y .. ']'
		end;
	};
}

-----------------------

local gfx = love.graphics

local function normal(n)
	if n == 0 then return 0 end
	return n/math.abs(n)
end

local function drawArc(c,r,a,x,y,s)
	local p = Vector2.new(-1,0)
	local q = (x-c):unit()
	local aq = q:perp():dot(p)
	local o = math.acos(p:dot(q))*-normal(aq)
	if a > 0 then o = o + math.pi end

	for i = 1,s do
		local a0 = (i-1)/s*a + o
		local a1 = i/s*a + o

		gfx.line(
			c.x + (math.cos(a0) * r), c.y - (math.sin(a0) * r),
			c.x + (math.cos(a1) * r), c.y - (math.sin(a1) * r)
		)
	end
end


local pressed = false
local p = 1
local points = {}
local tanAngle = -math.pi/4
local tanPos = Vector2.new()

function love.update()
	if pressed then
		if p == 0 and points[1] and points[2] then
			local t = Vector2.new(love.mouse.getPosition())
			local x = points[1]
			local y = points[2]

			local yx = y-x
			local yxu = yx:unit()
			local txu = (t-x):unit()
			local length = yx:magnitude()
			local aq = txu:perp():dot(yxu)
			local a = math.acos(txu:dot(yxu))*normal(aq)

			tanPos = Vector2.new(
				yxu.x*math.cos(a) - yxu.y*math.sin(a),
				yxu.x*math.sin(a) + yxu.y*math.cos(a)
			)*64 + x
			tanAngle = a
		elseif p > 0 and p <= #points then
			points[p].x,points[p].y = love.mouse.getPosition()
		end
	end
end

function love.draw()
	gfx.reset()
	gfx.setLineWidth(6)
	gfx.setPointSize(12)
	gfx.setBackgroundColor(102,102,102)

	for i = 2,#points do
		local a = points[i-1]
		local b = points[i]

		gfx.setColor(0,128,0)
		gfx.line(a.x,a.y,b.x,b.y)
	end

	if #points > 1 then
		local a = tanAngle
		for i = 1,#points-1 do
			local X = points[i]
			local Y = points[i+1]
			local Z = points[i+2]

			local r = (Y-X):magnitude()/2/math.sin(a)

			local YXu = (Y-X):unit()
			local a90 = a - math.pi/2
			local C = Vector2.new(
				YXu.x*math.cos(a90) - YXu.y*math.sin(a90),
				YXu.x*math.sin(a90) + YXu.y*math.cos(a90)
			)*r + X

			-- draw circle
		--	gfx.setColor(128,128,128,128)
		--	gfx.circle('fill',C.x,C.y,r,100)
		--	gfx.setColor(77,77,77,128)
		--	gfx.circle('line',C.x,C.y,r,100)

			-- draw arc
			gfx.setColor(255,0,0)
			drawArc(C,r,a*2,X,Y,100)

			-- draw radius
		--	gfx.setColor(0,0,128)
		--	gfx.line(X.x,X.y,C.x,C.y)

			-- draw center
		--	gfx.setColor(0,255,255)
		--	gfx.point(C.x,C.y)

			if Z then
				local YCu = (Y-C):unit()*normal(a)
				local YCup = YCu:perp()
				local ZYu = (Z-Y):unit()
				local aq = YCu:dot(ZYu)
				a = math.acos(YCup:dot(ZYu))*-normal(aq)

				-- draw tangent
			--	local p = YCup*64 + Y
			--	local q = -YCup*64 + Y
			--	gfx.setColor(128,0,0)
			--	gfx.line(p.x,p.y,q.x,q.y)
			end
		end
	end

	if #points > 1 then
		local x = points[1]
		local y = points[2]
		local yxu = (y-x):unit()

		tanPos = Vector2.new(
			yxu.x*math.cos(tanAngle) - yxu.y*math.sin(tanAngle),
			yxu.x*math.sin(tanAngle) + yxu.y*math.cos(tanAngle)
		)*64 + x

		gfx.setLineWidth(6)
		gfx.setColor(128,0,0)
		gfx.line(tanPos.x,tanPos.y,x.x,x.y)

		gfx.setLineWidth(1)
		gfx.setColor(128,0,0)
		gfx.circle('fill',tanPos.x,tanPos.y,6)
		gfx.setColor(255,255,255)
		gfx.circle('line',tanPos.x,tanPos.y,6)
	end

	gfx.setLineWidth(1)
	for i = 1,#points do
		local v = points[i]
		gfx.setColor(0,255,0)
		gfx.circle('fill',v.x,v.y,6)
		gfx.setColor(255,255,255)
		gfx.circle('line',v.x,v.y,6)
	end
end

function love.mousepressed(x,y,b)
	if b ~= 'l' and b ~= 'r' then return end

	local c = Vector2.new(x,y)

	if #points > 1 and b == 'l' then
		if (c-tanPos):magnitude() < 8 then
			p = 0
			pressed = true
			return
		end
	end

	local n
	for i = 1,#points do
		if (c-points[i]):magnitude() < 8 then
			n = i
			break
		end
	end

	if b == 'l' then
		if n then
			p = n
		else
			points[#points+1] = c
			p = #points
		end
		pressed = true
	elseif b == 'r' then
		if n and not pressed then
			table.remove(points,n)
		end
	end
end

function love.mousereleased(x,y,b)
	if b == 'l' then
		pressed = false
	end
end

function love.keypressed(k)
	if k == 'backspace' and not pressed then
		points = {}
	end
end