minor adjustment to vertical TextScroll: we shouldn't need to move the cursor to the very line in the visible area, or the ver first line in the visible area, to scroll. We scroll if the cursorLine is some distance close to either edge instead.

fcore/text-scroll.sml

@@ -26,18 +26,20 @@ struct
     end
 
   fun getStartLine (prevLineNumber, cursorLine, windowHeight) =
-    if cursorLine <= prevLineNumber then
-      (* if cursorLine is prior or same as prevLineNumber, 
-       * then use cursorLine as scroll-line-start *)
-      cursorLine
+    if cursorLine <= (prevLineNumber + 3) then
+      (* cursorLine is prior to or same as prevLineNumber,
+       * so use cursorLine to calculate the start line we want. *)
+      Int.max (cursorLine - 3, 0)
     else
       (* cursorLine > prevLineNumber *)
       let
         val howManyLinesWeCanFit = windowHeight div TC.ySpace
-        val howManyLinesWeCanFit = howManyLinesWeCanFit - 2
+        val howManyLinesWeCanFit = howManyLinesWeCanFit
       in
-        if cursorLine > prevLineNumber + howManyLinesWeCanFit then
-          cursorLine - howManyLinesWeCanFit
+        if cursorLine > prevLineNumber + (howManyLinesWeCanFit - 3) then
+          (* cursorLine is after the visible part of the screen
+           * so return the mimimum line where cursorLine is visible *)
+          cursorLine - howManyLinesWeCanFit + 3
         else
           prevLineNumber
       end