add ability to select cursor colour

fcore/app-with.sml

@@ -1115,6 +1115,62 @@ struct
       , xClickPoints = xClickPoints
       , yClickPoints = yClickPoints
 
+      , showGraph = showGraph
+      , openFilePath = openFilePath
+      , fileBrowser = fileBrowser
+      , fileBrowserIdx = fileBrowserIdx
+      , r = r
+      , g = g
+      , b = b
+      , a = a
+      , modalNum = 0
+      , undo = undo
+      , redo = redo
+      }
+    end
+
+  fun cursorColour (app, r, g, b, a) =
+    let
+      val
+        { mode
+        , canvasHeight
+        , canvasWidth
+        , squares
+        , arrowX
+        , arrowY
+        , windowWidth
+        , windowHeight
+        , xClickPoints
+        , yClickPoints
+
+        , showGraph
+        , mouseX
+        , mouseY
+        , openFilePath
+        , fileBrowser
+        , fileBrowserIdx
+        , r = _
+        , g = _
+        , b = _
+        , a = _
+        , modalNum
+        , undo
+        , redo
+        } = app
+    in
+      { mode = mode
+      , canvasHeight = canvasHeight
+      , canvasWidth = canvasWidth
+      , arrowX = arrowX
+      , mouseX = mouseX
+      , mouseY = mouseY
+      , squares = squares
+      , arrowY = arrowY
+      , windowWidth = windowWidth
+      , windowHeight = windowHeight
+      , xClickPoints = xClickPoints
+      , yClickPoints = yClickPoints
+
       , showGraph = showGraph
       , openFilePath = openFilePath
       , fileBrowser = fileBrowser

fcore/normal-mode.sml

@@ -263,6 +263,16 @@ struct
   fun updateBlue model = (AppWith.b model, [])
   fun updateAlpha model = (AppWith.a model, [])
 
+  fun selectCursorColour (model: app_type) =
+    let
+      val {squares, arrowX, arrowY, ...} = model
+      val yAxis = Vector.sub (squares, arrowX)
+      val {r, g, b, a} = Vector.sub (yAxis, arrowY)
+      val model = AppWith.cursorColour (model, r, g, b, a)
+    in
+      (model, [])
+    end
+
   fun updateCanvas (model, canvasWidth, canvasHeight) =
     let
       val
@@ -359,6 +369,7 @@ struct
     | KEY_G => updateGreen model
     | KEY_B => updateBlue model
     | KEY_A => updateAlpha model
+    | KEY_C => selectCursorColour model
     | KEY_W => updateCanvasWidth model
     | KEY_H => updateCanvasHeight model
     | KEY_M => enterMoveMode model