Added raycast function (#70)

* Added a raycast function

* Now raycast returns hit points instead of ray parameters.

* Added documentation for raycast function

* Fixed indentention

docs/MainModule.rst

@@ -254,6 +254,25 @@ You can iterate over the shapes using ``pairs`` (see example).
         game.selectUnit(s)
     end
 
+.. function:: HC.raycast(x, y, dx, dy, range)
+
+   :param numbers x,y: Origin point of ray
+   :param numbers dx,dy: Direction vector of ray(normal vector)
+   :param number range: Range of raycast
+   :returns: Table of shapes that got hit and its hit points.
+
+Gets shapes that got hit by a given ray and the points which that shape intersects with the ray.
+The table is a *set*, meaning that the shapes are stored in *keys* of the table. The values are the points of intersection. You can iterate over the shapes using ``pairs`` (see example).
+
+**Example**::
+
+    local hits = HC.raycast(originx, originy, directionx, directiony, range)
+    for shape, points in pairs(hits) do
+      for _, point in ipairs(points) do
+        love.graphics.points(point.x, point.y)
+      end
+    end
+
 
 .. function:: HC.hash()
 

init.lua

@@ -118,6 +118,30 @@ function HC:collisions(shape)
 	return candidates
 end
 
+function HC:raycast(x, y, dx, dy, range)
+	local dxr, dyr = dx * range, dy * range
+	local bbox = { x + dxr , y + dyr, x, y }
+	local candidates = self._hash:inSameCells(unpack(bbox))
+
+	for col in pairs(candidates) do
+		local rparams = col:intersectionsWithRay(x, y, dx, dy)
+		if #rparams > 0 then
+			for i, rparam in pairs(rparams) do
+				if rparam < 0 or rparam > range then
+					rawset(rparams, i, nil)
+				else
+					local hitx, hity = x + (rparam * dx), y + (rparam * dy)
+					rawset(rparams, i, { x = hitx, y = hity })
+				end
+			end
+			rawset(candidates, col, rparams)
+		else
+			rawset(candidates, col, nil)
+		end
+	end
+	return candidates
+end
+
 function HC:shapesAt(x, y)
 	local candidates = {}
 	for c in pairs(self._hash:cellAt(x, y)) do