begin parameterising level so that it fits into larger type (with different modes like TITLE, LEVEL, SETTINGS, etc.)

fcore/level/chain-edge.sml

@@ -0,0 +1,49 @@
+structure ChainEdgeRight =
+struct
+  fun lerp (startX, startY, drawWidth, drawHeight, windowWidth, windowHeight, r, g, b) : Real32.real vector =
+    let
+       val endY = windowHeight - startY
+       val startY = windowHeight - (startY + drawHeight)
+       val endX = startX + drawWidth
+       val windowHeight = windowHeight / 2.0
+       val windowWidth = windowWidth / 2.0
+    in
+       #[      (((startX * (1.0 - 0.0)) + (endX * 0.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.799999952316)) + (endY * 0.799999952316)) / windowHeight) - 1.0, 
+      r, g, b,
+
+      (((startX * (1.0 - 0.0)) + (endX * 0.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.200000017881)) + (endY * 0.200000017881)) / windowHeight) - 1.0,
+      r, g, b,
+
+      (((startX * (1.0 - 1.0)) + (endX * 1.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.485714316368)) + (endY * 0.485714316368)) / windowHeight) - 1.0, 
+      r, g, b
+    ]
+  end
+end
+
+structure ChainEdgeLeft =
+struct
+  fun lerp (startX, startY, drawWidth, drawHeight, windowWidth, windowHeight, r, g, b) : Real32.real vector =
+    let
+       val endY = windowHeight - startY
+       val startY = windowHeight - (startY + drawHeight)
+       val endX = startX + drawWidth
+       val windowHeight = windowHeight / 2.0
+       val windowWidth = windowWidth / 2.0
+    in
+       #[      (((startX * (1.0 - 1.0)) + (endX * 1.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.799999952316)) + (endY * 0.799999952316)) / windowHeight) - 1.0, 
+      r, g, b,
+
+      (((startX * (1.0 - 1.0)) + (endX * 1.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.200000017881)) + (endY * 0.200000017881)) / windowHeight) - 1.0, 
+      r, g, b,
+
+      (((startX * (1.0 - 0.0)) + (endX * 0.0)) / windowWidth) - 1.0,
+      (((startY * (1.0 - 0.485714316368)) + (endY * 0.485714316368)) / windowHeight) - 1.0, 
+      r, g, b
+    ]
+  end
+end