improve creation of click points, so that we can have a pixel be a perfect square, even if the canvas isn't

fcore/click-points.sml

@@ -1,12 +1,23 @@
 structure ClickPoints =
 struct
-  fun generate (start, finish, numPoints) =
+  fun generate (windowWidth, windowHeight, canvasWidth, canvasHeight) =
     let
-      val difference = finish - start
-      val increment = Real32.fromInt difference / Real32.fromInt numPoints
+      val realWindowWidth = Real32.fromInt windowWidth
+      val realCanvasWidth = Real32.fromInt canvasWidth
+      val realWindowHeight = Real32.fromInt windowHeight
+      val realCanvasHeight = Real32.fromInt canvasHeight
+
+      val xPixelSize = realWindowWidth / realCanvasWidth
+      val yPixelSize = realWindowHeight / realCanvasHeight
+
+      val pixelSize = Real32.min (xPixelSize, yPixelSize)
+
+      val xClickPoints = Vector.tabulate (canvasWidth + 1, fn i =>
+        Real32.fromInt i * pixelSize)
+      val yClickPoints = Vector.tabulate (canvasHeight + 1, fn i =>
+        Real32.fromInt i * pixelSize)
     in
-      Vector.tabulate (numPoints + 1, fn idx =>
-        (Real32.fromInt idx * increment))
+      (xClickPoints, yClickPoints)
     end
 
   fun getClickPos (clickPoints, mousePos, idx) =