pull in new version of brolib-sml so that we can get bug fixes for LineGap.getLineNumberOfIdx, delete the TextWindow structure (which was previously used to get the start line to draw from), and replace previous usages of TextWindow with TextScroll.getStartLine. This enables us to scroll in a way tailored to the reimplemented TextBuilder (which do not wrap lines or characters)

fcore/text-scroll.sml

@@ -34,12 +34,11 @@ struct
       (* cursorLine > prevLineNumber *)
       let
         val howManyLinesWeCanFit = windowHeight div TC.ySpace
+        val howManyLinesWeCanFit = howManyLinesWeCanFit - 2
       in
-        if prevLineNumber + howManyLinesWeCanFit >= cursorLine then
-          prevLineNumber
+        if cursorLine > prevLineNumber + howManyLinesWeCanFit then
+          cursorLine - howManyLinesWeCanFit
         else
-          let val lineDifference = cursorLine - prevLineNumber
-          in prevLineNumber + lineDifference
-          end
+          prevLineNumber
       end
 end