address one regression, where triangles were no longer being displayed (because calculation changed) after the previous refactoring. I know of only one more regression, which is that the clicked dots do not persist after moving the mouse.

functional-core/app/app-update.sml

@@ -18,7 +18,7 @@ struct
       val drawVec =
         case ClickPoints.getClickPositionFromMouse model of
           SOME (xpos, ypos) =>
-            ClickPoints.getDrawVec (xpos, ypos, 1.0, 0.0, 0.0, model)
+            ClickPoints.getDrawDot (xpos, ypos, 1.0, 0.0, 0.0, model)
         | NONE => Vector.fromList []
       val drawMsg = DRAW_DOT drawVec
     in
@@ -29,14 +29,16 @@ struct
     case ClickPoints.getClickPositionFromMouse model of
       SOME (xpos, ypos) =>
         let
-          val dotVec = ClickPoints.getDrawVec (xpos, ypos, 0.0, 0.0, 1.0, model)
+          val dotVec = ClickPoints.getDrawDot (xpos, ypos, 0.0, 0.0, 1.0, model)
+          
           val {windowWidth, windowHeight, ...} = model
           val halfWidth = Real32.fromInt (windowWidth div 2)
           val halfHeight = Real32.fromInt (windowHeight div 2)
           val hpos =
-            Ndc.centreAlignX (xpos, windowWidth, windowHeight, halfWidth)
+            ClickPoints.xposToNdc (xpos, windowWidth, windowHeight, halfWidth)
           val vpos =
-            Ndc.centreAlignY (ypos, windowWidth, windowHeight, halfHeight)
+            ClickPoints.yposToNdc (ypos, windowWidth, windowHeight, halfHeight)
+
           val newUndoTuple = (hpos, vpos)
         in
           (case #triangleStage model of
@@ -70,7 +72,6 @@ struct
                let
                  val model = AppWith.addTriangle
                    (model, x1, y1, x2, y2, hpos, vpos, newUndoTuple)
-
                  val drawVec = Triangles.toVector model
                  val drawMsg = DRAW_TRIANGLES_AND_RESET_DOTS drawVec
                in

functional-core/app/click-points.sml

@@ -3,7 +3,7 @@ sig
   val generate: int * int -> Real32.real vector
   val getClickPositionFromMouse: AppType.app_type
                                  -> (Real32.real * Real32.real) option
-  val getDrawVec:
+  val getDrawDot:
     Real32.real
     * Real32.real
     * Real32.real
@@ -11,6 +11,10 @@ sig
     * Real32.real
     * AppType.app_type
     -> Real32.real vector
+
+  (* two below functions convert pixel coordinates to normalised device coordinates *)
+  val xposToNdc: Real32.real * int * int * Real32.real -> Real32.real
+  val yposToNdc: Real32.real * int * int * Real32.real -> Real32.real
 end
 
 structure ClickPoints :> CLICK_POINTS =
@@ -53,7 +57,7 @@ struct
          | NONE => NONE)
     | NONE => NONE
 
-  fun getDrawVec (xpos, ypos, r, g, b, app: AppType.app_type) =
+  fun getDrawDot (xpos, ypos, r, g, b, app: AppType.app_type) =
     let
       val {windowWidth, windowHeight, ...} = app
 
@@ -71,4 +75,37 @@ struct
     in
       Ndc.ltrbToVertex (left, top, right, bottom, r, g, b)
     end
+
+  fun xposToNdc (xpos, windowWidth, windowHeight, halfWidth) =
+
+    let
+      val xpos = xpos - halfWidth
+
+    in
+      if windowWidth > windowHeight then
+        let
+          val difference = windowWidth - windowHeight
+          val offset = Real32.fromInt (difference div 2)
+        in
+          xpos / (halfWidth - offset)
+        end
+      else
+        xpos / halfWidth
+
+    end
+
+  fun yposToNdc (ypos, windowWidth, windowHeight, halfHeight) =
+    let
+      val ypos = ~(ypos - halfHeight)
+    in
+      if windowHeight > windowWidth then
+        let
+          val difference = windowHeight - windowWidth
+          val offset = Real32.fromInt (difference div 2)
+        in
+          ypos / (halfHeight - offset)
+        end
+      else
+        ypos / halfHeight
+    end
 end