nasty bug in scroll update i couldn't wrap my head around

ogui.ml

@@ -5,6 +5,7 @@ module Str = Re.Str
 
 type stroke = { width : float; color : Gv.Color.t }
 
+let debugsec = ref false
 let stroke_none = { width = 0.; color = Gv.Color.transparent }
 
 let pp_text_row : Gv.Text.text_row F.t =
@@ -456,7 +457,7 @@ module TextLayout = struct
           field "byte_range"
             (fun s -> s.byte_range)
             (pair ~sep:(any ",") int int);
-          field "format" (fun s -> s.format) pp_format;
+          (* field "format" (fun s -> s.format) pp_format; *)
         ])
 
   let section_default =
@@ -536,6 +537,9 @@ module TextLayout = struct
         List.fold_left
           (fun (l : section list) sec ->
             let s, e = sec.byte_range in
+            if !debugsec then
+              F.epr "with_range section cs=%d ce=%d s=%d e=%d@." cs ce
+                s e;
 
             l
             @ (if
@@ -570,6 +574,10 @@ module TextLayout = struct
   let with_cursor (cur : cursor) ?(format = default_cursor_formatter)
       layout : layout =
     let c = with_range (cur.index, cur.index + 1) ~format layout in
+    if !debugsec then
+      F.epr "with_cursor %a@."
+        F.(brackets @@ list ~sep:cut pp_section)
+        c.sections;
     c
 
   let with_mark (mark : int option) (cur : int)
@@ -776,27 +784,49 @@ module TextEdit = struct
     | Some start' ->
         if rows - 1 > 0 then index_rows_from s (start' + 1) (rows - 1)
         else Some (start' + 1)
-    | None -> None
+    | None -> None (* eof *)
+
+  let rec rindex_rows_from (s : string) (start : int) (rows : int) :
+      int option =
+    match String.rindex_from_opt s start '\n' with
+    | Some start' ->
+        if start' - 1 <= 0 then None
+        else if rows - 1 > 0 then
+          rindex_rows_from s (start' - 1) (rows - 1)
+        else Some (start' + 1)
+    | None -> None (* eof *)
 
   let scroll_update ({ text; cursor; scroll; rows; _ } as t : t) :
       unit Lwt.t =
-    F.epr "scroll_update cursor=%d scroll=%d rows=%d" cursor.index
-      scroll rows;
     TextBuffer.fold_string text (fun s ->
+        let slen = String.length s in
         (if cursor.index < scroll then
-           match String.rindex_from_opt s cursor.index '\n' with
+           match
+             String.rindex_from_opt s
+               (min (slen - 1) (cursor.index - 1))
+               '\n'
+           with
            | Some i' -> t.scroll <- i' + 1
            | None -> t.scroll <- 0
          else
            match index_rows_from s scroll rows with
-           | None -> (* eof *) ()
+           | None -> ()
            | Some eow -> (
-               F.epr " eow=%d" eow;
+               F.epr "eow=%d@." eow;
-               if cursor.index > eow then
+               if cursor.index >= eow then
-                 match String.index_from_opt s cursor.index '\n' with
+                 match
+                   rindex_rows_from s
+                     (min (slen - 1) cursor.index)
+                     rows
+                 with
                  | None -> ()
-                 | Some i' -> t.scroll <- i' + 1));
+                 | Some i' -> t.scroll <- i'));
-        F.epr "@.")
+        F.epr
+          "scroll_update slen=%d cursor=%d scroll=%d c-s=%d rows=%d@."
+          (String.length s) t.cursor.index t.scroll
+          (cursor.index - t.scroll)
+          rows;
+        debugsec := true)
 
   let cursor_update (t : t) (f : int -> int) : unit Lwt.t =
     col t >>= fun last_col ->
@@ -877,19 +907,19 @@ module TextEdit = struct
                          Str.search_backward (Str.regexp "^") s
                        in
                        let bol = sbol t.cursor.index in
-                       if bol > 0 then (
+                       if bol > 0 then
                          let prev_bol = sbol (max 0 (bol - 1)) in
                          let prev_line_len = bol - 1 - prev_bol in
-                         F.epr
+
+                         (*F.epr
                            "up: index=%d bol=%d prev_bol=%d \
                             prev_line_len=%d @."
-                           t.cursor.index bol prev_bol prev_line_len;
+                           t.cursor.index bol prev_bol prev_line_len; *)
-
                          prev_bol
                          +
                          if t.cursor.last_col > prev_line_len then
                            prev_line_len
-                         else min prev_line_len t.cursor.last_col)
+                         else min prev_line_len t.cursor.last_col
                        else t.cursor.index)
                    >>= cursor_set t);
              ]
@@ -1149,22 +1179,26 @@ module Painter = struct
     let contents_len = String.length contents in
     let row_count =
       Gv.Text.break_lines t ~break_width:(Box2.w rect) ~max_rows
-        ~lines contents
+        ~lines ~start:te.scroll contents
     in
     Seq.fold_left
-      (fun ((cur, next) : p2 * int) (row : Gv.Text.text_row) ->
+      (fun ((cur, start) : p2 * int) (row : Gv.Text.text_row) ->
-        F.epr "text_layout row=%a@." pp_text_row row;
+        if !debugsec then
+          F.epr "start=%d row=%a %a @." start pp_text_row row
+            F.(brackets @@ list TextLayout.pp_section)
+            g.sections;
+        debugsec := false;
         let sections =
           List.filter
             (fun (r : TextLayout.section) ->
               fst r.byte_range <= row.end_index
-              && snd r.byte_range > next)
+              && snd r.byte_range > start)
             g.sections
         in
         List.fold_left
           (fun (cur' : p2) (sec : TextLayout.section) ->
             let start, end_ =
-              ( next |> max (fst sec.byte_range) |> min contents_len,
+              ( start |> max (fst sec.byte_range) |> min contents_len,
                 row.end_index |> min contents_len
                 |> min (snd sec.byte_range) )
             in
@@ -1199,7 +1233,7 @@ module Painter = struct
           sections
         |> fun cur'' ->
         (V2.(v (max (x cur) (x cur'')) (y cur'')), row.next))
-      (Box2.o rect, 0)
+      (Box2.o rect, te.scroll)
       (Seq.take row_count (Array.to_seq lines))
     |> fst
     |> Box2.(of_pts (o rect))

oplevel.ml

@@ -109,9 +109,9 @@ let () =
                  (TextBuffer.of_repo
                     ~path:[ ".config"; "init.ml" ]
                     ~repo:rootrepo));
-            textedit
+            (*textedit
               (TextEdit.multiline ui
-                 (TextBuffer.of_repo ~path:[ "README" ] ~repo:rootrepo));
+                 (TextBuffer.of_repo ~path:[ "README" ] ~repo:rootrepo)); *)
           ])
   in
 
@@ -153,7 +153,11 @@ let () =
          Gl.enable Gl.cull_face_enum;
          Gl.disable Gl.depth_test;
 
-         let width, height = (float win_w, float win_h) in
+         let width, height =
+           ( float win_w,
+             float (win_h - 50)
+             (* TKTK might be an artifact of exwm or something *) )
+         in
          let box = Gg.(Box2.v V2.zero Size2.(v width height)) in
          Gv.begin_frame ctx ~width ~height ~device_ratio:1.;
          Perfgraph.render graph ctx (width -. 205.) 5.;