add function to get the appropriate scroll column

fcore/normal-mode/normal-finish.sml

@@ -14,6 +14,10 @@ struct
     let
       val {windowWidth, windowHeight, startLine, searchString, ...} = app
 
+      (* calculate scroll column *)
+      val buffer = LineGap.goToIdx (cursorIdx, buffer)
+      val visualScrollColumn = TextScroll.getScrollColumn (buffer, cursorIdx, windowWidth)
+
       (* move LineGap to first line displayed on screen *)
       val buffer = LineGap.goToLine (startLine, buffer)
 

fcore/text-constants.sml

@@ -4,5 +4,7 @@ struct
   val xSpace3 = xSpace * 3
   val ySpace = 25
   val scale: Real32.real = 2.0
-  val textLineWidth = xSpace * 80
+
+  val textLineCount = 80
+  val textLineWidth = xSpace * textLineCount
 end

fcore/text-scroll.sml

@@ -0,0 +1,22 @@
+structure TextScroll =
+struct
+  structure TC = TextConstants
+
+  (* Preqreuisite: move buffer to cursorIdx *)
+  fun getScrollColumn (buffer, cursorIdx, windowWidth) =
+    let
+      val startOfLine = Cursor.vi0 (buffer, cursorIdx)
+      val columnDifference = cursorIdx - startOfLine
+    in
+      if columnDifference = 0 then
+        0
+      else
+        let
+          val howManyColumnsCanWeFit =
+            if windowWidth >= TC.textLineWidth then TC.textLineCount
+            else windowWidth div TC.xSpace
+        in
+          columnDifference mod howManyColumnsCanWeFit
+        end
+    end
+end

shf.mlb

@@ -40,6 +40,7 @@ in
 end
 fcore/cursor.sml
 fcore/text-window.sml
+fcore/text-scroll.sml
 
 fcore/normal-mode/normal-finish.sml
 fcore/normal-mode/normal-search-finish.sml