[gnome-builder] Disable 'scroll-on-output' in build log panel

[Sébastien Lafargue <slafargue src gnome org>]

commit 60b5efe466d2dea347f41d53738068a6823ba11a
Author: kritarth <kritarth 3010 gmail com>
Date:   Mon Dec 12 23:59:35 2016 +0530

    Disable 'scroll-on-output' in build log panel
    
    Currently, the build log panel is bound to scroll to end whenever new output
    is added to the buffer using gtk_text_view_scroll_to_mark. In order to disable
    this auto-scrolling I added horizontal and vertical GtkAdjustments. These
    adjustments are initialised in gbp_build_log_panel_init(). They point to
    the adjustments of GtkScrolledWindow scroller. With these adjustments I check
    if the user has scrolled back or right manually.
    
    expression1: value >= upper - page_size - offset
    This expression returns true if the user has not scrolled vertically back.
    The 'offset' is defined as VERTICAL_AUTOSCROLL_TOLERENCE - this means the
    limit upto which scroll-on-output will still work even if the user has
    manually scrolled.
    
    Similarly HORIZONTAL_AUTOSCROLL_TOLERENCE is defined.
    Detection of horizontal scrolling is done by
    expression2: value <= HORIZONTAL_AUTOSCROLL_TOLERENCE
    HORIZONTAL_AUTOSCROLL_TOLERENCE is set to 3 because the left-margin of text_view is also set at 3.
    
    if (expression1 && expression2) then
            set the vertical adjustment to upper - page_size
            apply this adjustment to the container
    
    https://bugzilla.gnome.org/show_bug.cgi?id=775642

 plugins/build-tools/gbp-build-log-panel.c |   25 ++++++++++++++++++++++---
 1 files changed, 22 insertions(+), 3 deletions(-)
---
diff --git a/plugins/build-tools/gbp-build-log-panel.c b/plugins/build-tools/gbp-build-log-panel.c
index 59d02e0..a6a015c 100644
--- a/plugins/build-tools/gbp-build-log-panel.c
+++ b/plugins/build-tools/gbp-build-log-panel.c
@@ -25,6 +25,9 @@
 
 #include "gbp-build-log-panel.h"
 
+#define HORIZONTAL_AUTOSCROLL_TOLERENCE   3.0
+#define VERTICAL_AUTOSCROLL_TOLERENCE     30.0
+
 struct _GbpBuildLogPanel
 {
   PnlDockWidget      parent_instance;
@@ -38,6 +41,9 @@ struct _GbpBuildLogPanel
   GtkScrolledWindow *scroller;
   GtkTextView       *text_view;
   GtkTextTag        *stderr_tag;
+
+  GtkAdjustment     *hadjustment;
+  GtkAdjustment     *vadjustment;
 };
 
 enum {
@@ -92,13 +98,23 @@ gbp_build_log_panel_log (GbpBuildLogPanel  *self,
                          const gchar       *message,
                          IdeBuildResult    *result)
 {
-  GtkTextMark *insert;
   GtkTextIter iter;
+  gboolean h_scroll_left;
+  gboolean v_scroll_bottom;
+  gdouble last_page_pos;
 
   g_assert (GBP_IS_BUILD_LOG_PANEL (self));
   g_assert (message != NULL);
   g_assert (IDE_IS_BUILD_RESULT (result));
 
+  last_page_pos = gtk_adjustment_get_upper (self->vadjustment) -
+                  gtk_adjustment_get_page_size (self->vadjustment);
+  h_scroll_left =
+    gtk_adjustment_get_value (self->hadjustment) <= HORIZONTAL_AUTOSCROLL_TOLERENCE;
+  v_scroll_bottom =
+    gtk_adjustment_get_value (self->vadjustment) >= last_page_pos -
+                                                    VERTICAL_AUTOSCROLL_TOLERENCE;
+
   gtk_text_buffer_get_end_iter (self->buffer, &iter);
 
   if (G_LIKELY (log == IDE_BUILD_RESULT_LOG_STDOUT))
@@ -116,8 +132,8 @@ gbp_build_log_panel_log (GbpBuildLogPanel  *self,
       gtk_text_buffer_apply_tag (self->buffer, self->stderr_tag, &begin, &iter);
     }
 
-  insert = gtk_text_buffer_get_insert (self->buffer);
-  gtk_text_view_scroll_to_mark (self->text_view, insert, 0.0, TRUE, 0.0, 0.0);
+  if (v_scroll_bottom && h_scroll_left)
+    gtk_adjustment_set_value (self->vadjustment, last_page_pos);
 }
 
 void
@@ -270,4 +286,7 @@ gbp_build_log_panel_init (GbpBuildLogPanel *self)
                            self,
                            G_CONNECT_SWAPPED);
   gbp_build_log_panel_changed_font_name (self, "font-name", self->settings);
+
+  self->hadjustment = gtk_scrolled_window_get_hadjustment (self->scroller);
+  self->vadjustment = gtk_scrolled_window_get_vadjustment (self->scroller);
 }