Merge pull request #31 from Ragzouken/intersectionsRay

method to return all intersections, not just the first

polygon.lua

@@ -462,6 +462,50 @@ function Polygon:intersectsRay(x,y, dx,dy)
 	return tmin ~= math.huge, tmin
 end
 
+function Polygon:intersectionsRay(x,y, dx,dy)
+	--local p = vector(x,y)
+	--local v = vector(dx,dy)
+	local nx,ny = vector.perpendicular(dx,dy)
+	local wx,xy,det
+
+	local ts = {}
+	local q1,q2 = nil, self.vertices[#self.vertices]
+	for i = 1, #self.vertices do
+		q1,q2 = q2,self.vertices[i]
+		wx,wy = q2.x - q1.x, q2.y - q1.y
+		det = vector.det(dx,dy, wx,wy)
+
+		if det ~= 0 then
+			-- there is an intersection point. check if it lies on both
+			-- the ray and the segment.
+			local rx,ry = q2.x - x, q2.y - y
+			local l = vector.det(rx,ry, wx,wy) / det
+			local m = vector.det(dx,dy, rx,ry) / det
+			if m >= 0 and m <= 1 then
+				-- we cannot jump out early here (i.e. when l > tmin) because
+				-- the polygon might be concave
+				table.insert(ts, l)
+			end
+		else
+			-- lines parralel or incident. get distance of line to
+			-- anchor point. if they are incident, check if an endpoint
+			-- lies on the ray
+			local dist = vector.dot(q1.x-x,q1.y-y, nx,ny)
+			if dist == 0 then
+				local l = vector.dot(dx,dy, q1.x-x,q1.y-y)
+				local m = vector.dot(dx,dy, q2.x-x,q2.y-y)
+				if l >= m then
+					table.insert(ts, l)
+				else
+					table.insert(ts, m)
+				end
+			end
+		end
+	end
+
+	return ts
+end
+
 Polygon = common_local.class('Polygon', Polygon)
 newPolygon = function(...) return common_local.instance(Polygon, ...) end
 return Polygon

shapes.lua

@@ -213,6 +213,14 @@ function ConvexPolygonShape:intersectsRay(x,y, dx,dy)
 	return self._polygon:intersectsRay(x,y, dx,dy)
 end
 
+function ConcavePolygonShape:intersectionsRay(x,y, dx,dy)
+	return self._polygon:intersectionsRay(x,y, dx,dy)
+end
+
+function ConvexPolygonShape:intersectionsRay(x,y, dx,dy)
+	return self._polygon:intersectionsRay(x,y, dx,dy)
+end
+
 -- circle intersection if distance of ray/center is smaller
 -- than radius.
 -- with r(s) = p + d*s = (x,y) + (dx,dy) * s defining the ray and
@@ -240,13 +248,35 @@ function CircleShape:intersectsRay(x,y, dx,dy)
 	return true, math_min(s1,s2)/(2*a)
 end
 
+function CircleShape:intersectionsRay(x,y, dx,dy)
+	local pcx,pcy = x-self._center.x, y-self._center.y
+
+	local a = vector.len2(dx,dy)
+	local b = 2 * vector.dot(dx,dy, pcx,pcy)
+	local c = vector.len2(pcx,pcy) - self._radius * self._radius
+	local discr = b*b - 4*a*c
+
+	if discr < 0 then return {} end
+
+	discr = math_sqrt(discr)
+	local s1, s2 = (discr-b)/(2*a), (-discr-b)/(2*a)
+
+	return {math.min(s1, s2), math.max(s1, s2)}
+end
+
 -- point shape intersects ray if it lies on the ray
-function PointShape:intersectsRay(x,y,dx,dy)
+function PointShape:intersectsRay(x,y, dx,dy)
 	local px,py = self._pos.x-x, self._pos.y-y
 	local t = vector.dot(px,py, dx,dy) / vector.len2(dx,dy)
 	return t >= 0, t
 end
 
+function PointShape:intersectionsRay(x,y, dx,dy)
+	local px,py = self._pos.x-x, self._pos.y-y
+	local t = vector.dot(px,py, dx,dy) / vector.len2(dx,dy)
+	return {t}
+end
+
 --
 -- auxiliary
 --