progress with refactoring

temp-squares/fcore/ndc.sml

@@ -1,6 +1,7 @@
 structure Ndc = 
 struct
   (* ndc = normalised device coordinates *)
+
   fun ltrbToVertex (left, top, right, bottom) =
     #[ left, bottom
      , right, bottom
@@ -20,4 +21,36 @@ struct
      , right, bottom, r, g, b
      , right, top, r, g, b
      ]
+
+  fun fromPixelX (xpos, windowWidth, windowHeight) =
+    let
+      val halfWidth = (Real32.fromInt windowWidth) / 2.0
+      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 fromPixelY (ypos, windowWidth, windowHeight) =
+    let
+      val halfHeight = (Real32.fromInt windowHeight) / 2.0
+      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