slight refactoring (move pure parsing functions to functional core in a separate file)

functional-core/app/ndc.sml

@@ -0,0 +1,41 @@
+structure Ndc = 
+struct
+  (* ndc = normalised device coordinates *)
+
+  fun ltrbToVertex (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
+     ]
+
+  (* This function adjusts the x position to be centre-aligned to the grid
+   * if windowWidth is greater than height 
+   * (where screen size does not have 1:1 aspect ratio). *)
+  fun centreAlignX (x, windowWidth, windowHeight, halfWidth) =
+    if windowWidth > windowHeight then
+      let
+        val difference = windowWidth - windowHeight
+        val offset = Real32.fromInt (difference div 2)
+      in
+        x * (halfWidth - offset)
+      end
+    else
+      x * halfWidth
+
+  (* Similar to centreAlignX, except it centre-aligns the y-point
+   * when windowHeight is greater than windowWidth. *)
+  fun centreAlignY (y, windowWidth, windowHeight, halfHeight) =
+    if windowHeight > windowWidth then
+      let
+        val difference = windowHeight - windowWidth
+        val offset = Real32.fromInt (difference div 2)
+      in
+        y * (halfHeight - offset)
+      end
+    else
+      y * halfHeight
+end