diff --git a/message-types/update-msg.sml b/message-types/update-msg.sml
index 74e4d9c..2b832b0 100644
--- a/message-types/update-msg.sml
+++ b/message-types/update-msg.sml
@@ -1,7 +1,2 @@
-signature UPDATE_MESSAGE =
-sig
-  datatype t = DRAW of DrawMessage.t | FILE of FileMessage.t
-end
-
-structure UpdateMessage :> UPDATE_MESSAGE =
+structure UpdateMessage =
 struct datatype t = DRAW of DrawMessage.t | FILE of FileMessage.t end
diff --git a/temp-squares/fcore/app-update.sml b/temp-squares/fcore/app-update.sml
new file mode 100644
index 0000000..c0005c8
--- /dev/null
+++ b/temp-squares/fcore/app-update.sml
@@ -0,0 +1,44 @@
+structure AppUpdate =
+struct
+  open AppType
+
+  open DrawMessage
+  open FileMessage
+  open InputMessage
+  open UpdateMessage
+
+  fun getDotVecFromIndices (model: app_type, hIdx, vIdx) =
+    let
+      val {windowWidth, windowHeight, xClickPoints, yClickPoints, ...} = model
+      val xpos = Vector.sub (xClickPoints, hIdx)
+      val ypos = Vector.sub (yClickPoints, vIdx)
+
+      val endXpos =
+        if hIdx + 1 = Vector.length xClickPoints then
+          xpos
+        else
+          Vector.sub (xClickPoints, hIdx + 1)
+
+      val endYpos =
+        if vIdx + 1 = Vector.length yClickPoints then
+          ypos
+        else
+          Vector.sub (yClickPoints, vIdx + 1)
+
+      val tl =
+        ClickPoints.getDrawDotRgb
+          (xpos, ypos, 1.0, 0.0, 0.0, windowWidth, windowHeight)
+      val tr =
+        ClickPoints.getDrawDotRgb
+          (endXpos, ypos, 1.0, 0.0, 0.0, windowWidth, windowHeight)
+      val bl =
+        ClickPoints.getDrawDotRgb
+          (xpos, endYpos, 1.0, 0.0, 0.0, windowWidth, windowHeight)
+      val br =
+        ClickPoints.getDrawDotRgb
+          (endXpos, endYpos, 1.0, 0.0, 0.0, windowWidth, windowHeight)
+    in
+      Vector.concat [tl, tr, bl, br]
+    end
+
+end
diff --git a/temp-squares/fcore/click-points.sml b/temp-squares/fcore/click-points.sml
index 16df628..d0922de 100644
--- a/temp-squares/fcore/click-points.sml
+++ b/temp-squares/fcore/click-points.sml
@@ -9,4 +9,38 @@ struct
       Vector.tabulate (numPoints + 1, fn idx =>
         (Real32.fromInt idx * increment) + start)
     end
+
+  fun getDrawDot (xpos, ypos, windowWidth, windowHeight) =
+    let
+      (* calculate normalised device coordinates *)
+      val halfWidth = Real32.fromInt (windowWidth div 2)
+      val halfHeight = Real32.fromInt (windowHeight div 2)
+      val hpos = xpos - halfWidth
+      val vpos = ~(ypos - halfHeight)
+
+      (* coordinates to form small box around clicked area *)
+      val left = (hpos - 5.0) / halfWidth
+      val right = (hpos + 5.0) / halfWidth
+      val bottom = (vpos - 5.0) / halfHeight
+      val top = (vpos + 5.0) / halfHeight
+    in
+      Ndc.ltrbToVertex (left, top, right, bottom)
+    end
+
+  fun getDrawDotRgb (xpos, ypos, r, g, b, windowWidth, windowHeight) =
+    let
+      (* calculate normalised device coordinates *)
+      val halfWidth = Real32.fromInt (windowWidth div 2)
+      val halfHeight = Real32.fromInt (windowHeight div 2)
+      val hpos = xpos - halfWidth
+      val vpos = ~(ypos - halfHeight)
+
+      (* coordinates to form small box around clicked area *)
+      val left = (hpos - 5.0) / halfWidth
+      val right = (hpos + 5.0) / halfWidth
+      val bottom = (vpos - 5.0) / halfHeight
+      val top = (vpos + 5.0) / halfHeight
+    in
+      Ndc.ltrbToVertexRgb (left, top, right, bottom, r, g, b)
+    end
 end
diff --git a/temp-squares/fcore/ndc.sml b/temp-squares/fcore/ndc.sml
new file mode 100644
index 0000000..79926cd
--- /dev/null
+++ b/temp-squares/fcore/ndc.sml
@@ -0,0 +1,23 @@
+structure Ndc = 
+struct
+  (* ndc = normalised device coordinates *)
+  fun ltrbToVertex (left, top, right, bottom) =
+    #[ left, bottom
+     , right, bottom
+     , left, top
+
+     , left, top
+     , right, bottom
+     , right, top
+     ]
+
+  fun ltrbToVertexRgb (left, top, right, bottom, r, g, b) =
+    #[ left, bottom, r, g, b
+     , right, bottom, r, g, b
+     , left, top, r, g, b
+
+     , left, top, r, g, b
+     , right, bottom, r, g, b
+     , right, top, r, g, b
+     ]
+end
diff --git a/temp-squares/message-types/update-msg.sml b/temp-squares/message-types/update-msg.sml
new file mode 100644
index 0000000..2b832b0
--- /dev/null
+++ b/temp-squares/message-types/update-msg.sml
@@ -0,0 +1,2 @@
+structure UpdateMessage =
+struct datatype t = DRAW of DrawMessage.t | FILE of FileMessage.t end
diff --git a/temp-squares/temp.mlb b/temp-squares/temp.mlb
index 0616129..9e9149d 100644
--- a/temp-squares/temp.mlb
+++ b/temp-squares/temp.mlb
@@ -2,16 +2,22 @@ $(SML_LIB)/basis/basis.mlb
 
 (* FUNCTIONAL CORE *)
 fcore/app-type.sml
-fcore/click-points.sml
-fcore/app-init.sml
-fcore/app-with.sml
 
 ann
   "allowVectorExps true"
 in
+  fcore/ndc.sml
   fcore/graph-lines.sml
 end
 
+fcore/click-points.sml
+fcore/app-init.sml
+fcore/app-with.sml
+
 message-types/draw-msg.sml
 message-types/file-msg.sml
 message-types/input-msg.sml
+message-types/update-msg.sml
+
+fcore/app-update.sml
+