[gnome-builder/wip/libide] libide: add helper to get visible rect w/ scroll offset

[Christian Hergert <chergert src gnome org>]

commit 5069fa906b1d68bcd911cf7eb653ba6c225b2bd1
Author: Christian Hergert <christian hergert me>
Date:   Mon Mar 9 01:13:32 2015 -0700

    libide: add helper to get visible rect w/ scroll offset

 libide/ide-source-view.c |   71 ++++++++++++++++++++++++++++++++++++++++++++++
 libide/ide-source-view.h |    2 +
 2 files changed, 73 insertions(+), 0 deletions(-)
---
diff --git a/libide/ide-source-view.c b/libide/ide-source-view.c
index 2cfad5b..aea4da9 100644
--- a/libide/ide-source-view.c
+++ b/libide/ide-source-view.c
@@ -93,7 +93,9 @@ typedef struct
 
   gint                         target_line_offset;
   guint                        count;
+
   guint                        scroll_offset;
+  guint                        cached_line_height;
 
   guint                        saved_line;
   guint                        saved_line_offset;
@@ -1669,6 +1671,28 @@ ide_source_view_query_tooltip (GtkWidget  *widget,
 }
 
 static void
+ide_source_view_real_style_updated (GtkWidget *widget)
+{
+  IdeSourceView *self = (IdeSourceView *)widget;
+  IdeSourceViewPrivate *priv = ide_source_view_get_instance_private (self);
+  PangoContext *context;
+  PangoLayout *layout;
+  int width;
+  int height;
+
+  g_assert (IDE_IS_SOURCE_VIEW (self));
+
+  GTK_WIDGET_CLASS (ide_source_view_parent_class)->style_updated (widget);
+
+  context = gtk_widget_get_pango_context (widget);
+  layout = pango_layout_new (context);
+  pango_layout_set_text (layout, "X", 1);
+  pango_layout_get_pixel_size (layout, &width, &height);
+  priv->cached_line_height = height;
+  g_object_unref (layout);
+}
+
+static void
 ide_source_view_real_action (IdeSourceView *self,
                              const gchar   *prefix,
                              const gchar   *action_name,
@@ -2743,6 +2767,7 @@ ide_source_view_class_init (IdeSourceViewClass *klass)
 
   widget_class->key_press_event = ide_source_view_key_press_event;
   widget_class->query_tooltip = ide_source_view_query_tooltip;
+  widget_class->style_updated = ide_source_view_real_style_updated;
 
   text_view_class->insert_at_cursor = ide_source_view_real_insert_at_cursor;
 
@@ -3569,3 +3594,49 @@ ide_source_view_set_scroll_offset (IdeSourceView *self,
       g_object_notify_by_pspec (G_OBJECT (self), gParamSpecs [PROP_SCROLL_OFFSET]);
     }
 }
+
+/**
+ * ide_source_view_get_visible_rect:
+ * @self: An #IdeSourceView.
+ * @visible_rect: (out): A #GdkRectangle.
+ *
+ * Gets the visible region in buffer coordinates that is the visible area of the buffer. This
+ * is similar to gtk_text_view_get_visible_area() except that it takes into account the
+ * #IdeSourceView:scroll-offset property to ensure there is space above and below the
+ * visible_rect.
+ */
+void
+ide_source_view_get_visible_rect (IdeSourceView *self,
+                                  GdkRectangle  *visible_rect)
+{
+  IdeSourceViewPrivate *priv = ide_source_view_get_instance_private (self);
+  GtkTextView *text_view = (GtkTextView *)self;
+  GdkRectangle area;
+
+  g_return_if_fail (IDE_IS_SOURCE_VIEW (self));
+  g_return_if_fail (visible_rect);
+
+  gtk_text_view_get_visible_rect (text_view, &area);
+
+  /*
+   * If we don't have valid line height, not much we can do now. We can just adjust things
+   * later once it becomes available.
+   */
+  if (priv->cached_line_height)
+    {
+      gint max_scroll_offset;
+      gint scroll_offset;
+      gint visible_lines;
+      gint scroll_offset_height;
+
+      visible_lines = area.height / priv->cached_line_height;
+      max_scroll_offset = (visible_lines - 1) / 2;
+      scroll_offset = MIN (priv->scroll_offset, max_scroll_offset);
+      scroll_offset_height = priv->cached_line_height * scroll_offset;
+
+      area.y += scroll_offset_height;
+      area.height -= (2 * scroll_offset_height);
+    }
+
+  *visible_rect = area;
+}
diff --git a/libide/ide-source-view.h b/libide/ide-source-view.h
index fda3d42..f91eda5 100644
--- a/libide/ide-source-view.h
+++ b/libide/ide-source-view.h
@@ -280,6 +280,8 @@ void                        ide_source_view_set_snippet_completion    (IdeSource
                                                                        gboolean                    
snippet_completion);
 void                        ide_source_view_set_back_forward_list     (IdeSourceView              *self,
                                                                        IdeBackForwardList         
*back_forward_list);
+void                        ide_source_view_get_visible_rect          (IdeSourceView              *self,
+                                                                       GdkRectangle               
*visible_rect);
 
 G_END_DECLS