LÖVE

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function is_point_in_triangle(p, t)
	local a = {
		 t[2].x*t[3].y,
		-t[2].y*t[3].x,
		 t[1].x*( t[2].y-t[3].y),
		 t[1].y*(-t[2].x+t[3].x)
	}
	local b = {
		 t[1].x*t[2].y,
		-t[1].y*t[2].x,
		p.x*(t[1].y-t[2].y),
		p.y*(t[2].x-t[1].x)
	}
	local c = {
		 t[1].y*t[3].x,
		-t[1].x*t[3].y,
		 p.x*(t[3].y-t[1].y),
		 p.y*(t[1].x-t[3].x)
	}
	local sa = a[1]+a[2]+a[3]+a[4]
	local sb = b[1]+b[2]+b[3]+b[4]
	local sc = c[1]+c[2]+c[3]+c[4]
	local sign = (sa>=0) and 1 or -1
	if (sign*sb>0) and (sign*sc>0) and (sb+sc)<(sign*sa) then
		return true
	else
		return false
	end
end

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if sign*sb<0 then return false end

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function pointInTriangle(p, t)
  local px, py, x1, y1, x2, y2, x3, y3 = p.x, p.y, t[1].x, t[1].y, t[2].x, t[2].y, t[3].x, t[3].y
  local ax, ay = x1 - px, y1 - py
  local bx, by = x2 - px, y2 - py
  local cx, cy = x3 - px, y3 - py
  local sab = ax*by - ay*bx < 0
  if sab ~= (bx*cy - by*cx < 0) then
    return false
  end
  return sab == (cx*ay - cy*ax < 0)
end

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function love.load()
	v1 = {x = 200, y = 200}
	v2 = {x = 400, y = 250}
	v3 = {x = 250, y = 500}
	inside = false
end

local function isPointInTriangle(point, v1, v2, v3)
	local function calculateTriangleArea(v1, v2, v3)
		return 0.5 * math.abs((v1.x - v3.x) * (v2.y - v1.y) - (v1.x - v2.x) * (v3.y - v1.y))
	end
	local totalArea = calculateTriangleArea(v1, v2, v3)
	local area1 = calculateTriangleArea(point, v2, v3)
	local area2 = calculateTriangleArea(v1, point, v3)
	local area3 = calculateTriangleArea(v1, v2, point)
	return math.abs(totalArea - (area1 + area2 + area3)) < 1e-6
end

function love.draw()
	if inside then
		love.graphics.setColor(0,1,1)
	else
		love.graphics.setColor(1,0,0)
	end
	love.graphics.line(v1.x, v1.y, v2.x, v2.y)
	love.graphics.line(v2.x, v2.y, v3.x, v3.y)
	love.graphics.line(v3.x, v3.y, v1.x, v1.y)
	love.graphics.circle ('line', v3.x, v3.y, 5)
end

function love.mousemoved(x, y)
	inside = isPointInTriangle({x=x, y=y}, v1, v2, v3)
end

function love.mousepressed(x, y)
	v2, v3 = v3, v2
	inside = isPointInTriangle({x=x, y=y}, v1, v2, v3)
end

Code: Select all

local function pointInPolygon (px, py, ...)
	local vertices = {...}
	local inside = false
	local j = #vertices-1
	local x2, y2 = vertices[j], vertices[j+1]

	for i = 1, #vertices-1, 2 do
		local x1, y1 = vertices[i], vertices[i+1]
		if (y1 < py and y2 >= py or y2 < py and y1 >= py)
		and (x1 <= px or x2 <= px)
		and (x1 + (py - y1) / (y2-y1)*(x2-x1) < px) then
			inside = not inside
		end
		x2, y2 = x1, y1
	end
	return inside
end

function love.mousemoved(x, y)
	inside = isPointInTriangle({x=x, y=y}, v1, v2, v3)

	local inside2 = pointInPolygon (x, y, v1.x, v1.y, v2.x, v2.y, v3.x, v3.y)
	love.window.setTitle (tostring (inside2))
end