diff --git a/src/main.lua b/src/main.lua
index 6fe3453..ec49305 100644
--- a/src/main.lua
+++ b/src/main.lua
@@ -74,6 +74,32 @@ local function load(name)
     content = textutils.unserialiseJSON(content)
     return content["buf"],content["dimensions"]
 end
+local function bufistype(buf, x,y,z, targettype)
+    return buf[posasstring(x,y,z)] == targettype or (targettype == 0 and not buf[posasstring(x,y,z)])
+end
+local function fill_getneighbors(x,y,z, sx,sz, seltype,buf)
+    local out = {}
+    if x ~= sx and bufistype(buf, x+1,y,z, seltype) then table.insert(out, {x+1,z}) end
+    if x ~= 1 and bufistype(buf, x-1,y,z, seltype) then table.insert(out, {x-1,z}) end
+    if z ~= sz and bufistype(buf, x,y,z+1, seltype) then table.insert(out, {x,z+1}) end
+    if z ~= 1 and bufistype(buf, x,y,z-1, seltype) then table.insert(out, {x,z-1}) end
+    return out
+end
+local function fill(ntype, x,y,z, buf, sx,sz)
+    local inittype = buf[posasstring(x,y,z)]
+
+    local neighbors = fill_getneighbors(x,y,z, sx,sz, inittype,buf)
+    buf[posasstring(x,y,z)] = ntype
+    while #neighbors > 0 do
+        local cn = table.remove(neighbors, 1)
+        local cx,cz = cn[1],cn[2]
+        local newneigh = fill_getneighbors(cx,y,cz, sx,sz, inittype,buf)
+        for _,v in pairs(newneigh) do
+            table.insert(neighbors, newneigh)
+        end
+        buf[posasstring(x,y,z)] = ntype
+    end
+end
 local function newdesign()
     local buf = {}
     local dimensions = {
@@ -102,6 +128,9 @@ local function newdesign()
             term.blit("W", colors.toBlit(colors.black), colors.toBlit(colors.white))
         end
     end
+    local shift = false
+
+    fill()
 
     while true do
         -- render buf
@@ -142,12 +171,21 @@ local function newdesign()
             event[4] = event[4]-camy
             if event[3] <= dimensions["x"] and event[4] <= dimensions["z"] then
                 if event[2] == 1 then -- left button, set
+                    if shift then
+                        fill(1, event[3],currentfloor,event[4], buf,dimensions["x"],dimensions["z"])
+                    end
                     buf[posasstring(event[3], currentfloor, event[4])] = 1
                 end
                 if event[2] == 3 then -- middle button, set special block
+                    if shift then
+                        fill(currentblock, event[3],currentfloor,event[4], buf,dimensions["x"],dimensions["z"])
+                    end
                     buf[posasstring(event[3], currentfloor, event[4])] = currentblock
                 end
                 if event[2] == 2 then -- right button, erase
+                    if shift then
+                        fill(0, event[3],currentfloor,event[4], buf,dimensions["x"],dimensions["z"])
+                    end
                     buf[posasstring(event[3], currentfloor, event[4])] = 0
                 end
             end
@@ -162,6 +200,9 @@ local function newdesign()
             currentblock = blocks[blockindex]
         end
         if event[1] == "key" then
+            if keys.getName(event[2]) == "leftShift" then
+                shift = true
+            end
             if keys.getName(event[2]) == "leftCtrl" then -- menu
                 local action = selopt({
                     "Save",
@@ -240,6 +281,9 @@ local function newdesign()
                 camx = camx - 1
             end
         end
+        if event[1] == "key_up" then
+            if keys.getName(event[2]) == "leftShift" then shift = false end
+        end
     end
 end
 local function move(direction)