Allows traversing the spatialhash with a ray

spatialhash.lua

@@ -148,6 +148,43 @@ function Spatialhash:update(obj, old_x1,old_y1, old_x2,old_y2, new_x1,new_y1, ne
     end
 end
 
+function Spatialhash:intersectionsWithSegment(x1, y1, x2, y2)
+    local odx, ody = x2 - x1, y2 - y1
+    local len, cur = vector.len(odx, ody), 0
+    local dx, dy = vector.normalize(odx, ody)
+    local step = self.cell_size / 2
+    local visited = {}
+    local points = {}
+    local mt = math.huge
+
+    while (cur + step < len) do
+        local cx, cy = x1 + dx * cur,  y1 + dy * cur
+        local shapes = self:cellAt(cx, cy)
+        cur = cur + step
+
+        for _, shape in pairs(shapes) do
+            if (not visited[shape]) then
+                local ints = shape:intersectionsWithRay(x1, y1, dx, dy)
+
+                for _, t in ipairs(ints) do
+                    if (t >= 0 and t <= len) then
+                        local px, py = vector.add(x1, y1, vector.mul(t, dx, dy))
+                        table.insert(points, {shape, t, px, py})
+                    end
+                end
+
+                visited[shape] = true
+            end
+        end
+    end
+
+    table.sort(points, function(a, b)
+        return a[2] < b[2]
+    end)
+
+    return points
+end
+
 function Spatialhash:draw(how, show_empty, print_key)
     if show_empty == nil then show_empty = true end
     for k1,v in pairs(self.cells) do