Use premove rather than start of moverect to implement scrollback pus…

…h in screen layer

src/screen.c

@@ -214,18 +214,25 @@ static void sb_pushline_from_row(VTermScreen *screen, int row)
   (screen->callbacks->sb_pushline)(screen->cols, screen->sb_buffer, screen->cbdata);
 }
 
-static int moverect_internal(VTermRect dest, VTermRect src, void *user)
+static int premove(VTermRect rect, void *user)
 {
   VTermScreen *screen = user;
 
   if(screen->callbacks && screen->callbacks->sb_pushline &&
-     dest.start_row == 0 && dest.start_col == 0 &&        // starts top-left corner
-     dest.end_col == screen->cols &&                      // full width
+     rect.start_row == 0 && rect.start_col == 0 &&        // starts top-left corner
+     rect.end_col == screen->cols &&                      // full width
      screen->buffer == screen->buffers[BUFIDX_PRIMARY]) { // not altscreen
-    for(int row = 0; row < src.start_row; row++)
+    for(int row = 0; row < rect.end_row; row++)
       sb_pushline_from_row(screen, row);
   }
 
+  return 1;
+}
+
+static int moverect_internal(VTermRect dest, VTermRect src, void *user)
+{
+  VTermScreen *screen = user;
+
   int cols = src.end_col - src.start_col;
   int downward = src.start_row - dest.start_row;
 
@@ -840,6 +847,7 @@ static int sb_clear(void *user) {
 static VTermStateCallbacks state_cbs = {
   .putglyph    = &putglyph,
   .movecursor  = &movecursor,
+  .premove     = &premove,
   .scrollrect  = &scrollrect,
   .erase       = &erase,
   .setpenattr  = &setpenattr,
@@ -884,6 +892,7 @@ static VTermScreen *screen_new(VTerm *vt)
   screen->sb_buffer = vterm_allocator_malloc(screen->vt, sizeof(VTermScreenCell) * cols);
 
   vterm_state_set_callbacks(screen->state, &state_cbs, screen);
+  vterm_state_callbacks_has_premove(screen->state);
 
   return screen;
 }

t/62screen_damage.test

@@ -146,9 +146,9 @@ PUSH "\e[25H\r\nABCDE\b\b\b\e[2P\r\n"
   sb_pushline 80 =
   moverect 1..25,0..80 -> 0..24,0..80
   damage 24..25,0..80 = 24<41 42 43 44 45>
+  sb_pushline 80 =
   moverect 24..25,4..80 -> 24..25,2..78
   damage 24..25,78..80
-  sb_pushline 80 =
 DAMAGEFLUSH
   moverect 1..25,0..80 -> 0..24,0..80
   damage 24..25,0..80