[gnome-builder/wip/vim] vim: try to clone VIM page up/down semantics more closely

[Christian Hergert <chergert src gnome org>]

commit 4e012b1c21986e86397a5eee662d76d5c8efdaf1
Author: Christian Hergert <christian hergert me>
Date:   Thu Oct 2 02:43:52 2014 -0700

    vim: try to clone VIM page up/down semantics more closely
    
    Gtk does it's own thing. VIM tries to place the bottom visible region
    right near the top on page down, and opposite on page up.
    
    This still gives us nice scrolling since it uses built in scrolling.
    
    Selections are also preseved.

 src/editor/gb-editor-vim.c |   72 +++++++++++++++++++++++++++++++++++++------
 1 files changed, 62 insertions(+), 10 deletions(-)
---
diff --git a/src/editor/gb-editor-vim.c b/src/editor/gb-editor-vim.c
index e5c32f6..6ef6155 100644
--- a/src/editor/gb-editor-vim.c
+++ b/src/editor/gb-editor-vim.c
@@ -1694,27 +1694,79 @@ gb_editor_vim_move_to_line_n (GbEditorVim *vim,
 }
 
 static void
+gb_editor_vim_move_to_iter (GbEditorVim *vim,
+                            GtkTextIter *iter,
+                            gdouble      yalign)
+{
+  GtkTextBuffer *buffer;
+  GtkTextMark *insert;
+
+  g_assert (GB_IS_EDITOR_VIM (vim));
+  g_assert (iter);
+  g_assert (yalign >= 0.0);
+  g_assert (yalign <= 1.0);
+
+  buffer = gtk_text_view_get_buffer (vim->priv->text_view);
+  insert = gtk_text_buffer_get_insert (buffer);
+
+  if (gtk_text_buffer_get_has_selection (buffer))
+    {
+      gtk_text_buffer_move_mark (buffer, insert, iter);
+      gb_editor_vim_ensure_anchor_selected (vim);
+    }
+  else
+    gtk_text_buffer_select_range (buffer, iter, iter);
+
+  gtk_text_view_scroll_to_iter (vim->priv->text_view, iter, 0.0,
+                                TRUE, 0.0, yalign);
+}
+
+static void
 gb_editor_vim_page_up (GbEditorVim *vim)
 {
+  GdkRectangle rect;
+  GtkTextIter iter;
+  guint offset;
+  gint line;
+
   g_assert (GB_IS_EDITOR_VIM (vim));
 
-  g_signal_emit_by_name (vim->priv->text_view,
-                         "move-cursor",
-                         GTK_MOVEMENT_PAGES,
-                         -1,
-                         FALSE);
+  gtk_text_view_get_visible_rect (vim->priv->text_view, &rect);
+  gtk_text_view_get_iter_at_location (vim->priv->text_view, &iter,
+                                      rect.x, rect.y);
+
+  line = MAX (0, gtk_text_iter_get_line (&iter) + 3);
+  gtk_text_iter_set_line (&iter, line);
+
+  for (offset = vim->priv->target_line_offset; offset; offset--)
+    if (gtk_text_iter_ends_line (&iter) || !gtk_text_iter_forward_char (&iter))
+      break;
+
+  gb_editor_vim_move_to_iter (vim, &iter, 1.0);
 }
 
 static void
 gb_editor_vim_page_down (GbEditorVim *vim)
 {
+  GdkRectangle rect;
+  GtkTextIter iter;
+  guint offset;
+  gint line;
+
   g_assert (GB_IS_EDITOR_VIM (vim));
 
-  g_signal_emit_by_name (vim->priv->text_view,
-                         "move-cursor",
-                         GTK_MOVEMENT_PAGES,
-                         1,
-                         FALSE);
+  gtk_text_view_get_visible_rect (vim->priv->text_view, &rect);
+  gtk_text_view_get_iter_at_location (vim->priv->text_view, &iter,
+                                      rect.x, rect.y + rect.height);
+
+  line = MAX (0, gtk_text_iter_get_line (&iter) - 3);
+  gtk_text_iter_set_line (&iter, line);
+
+  for (offset = vim->priv->target_line_offset; offset; offset--)
+    if (gtk_text_iter_ends_line (&iter) || !gtk_text_iter_forward_char (&iter))
+      break;
+
+  gb_editor_vim_move_to_iter (vim, &iter, 0.0);
 }
 
 static gboolean