[gnome-builder] editor: add grid design to Builder style scheme

[Christian Hergert <chergert src gnome org>]

commit 2922a92466f8cf01cad3e0615d5c9b05558cdd7b
Author: Christian Hergert <christian hergert me>
Date:   Mon Nov 17 20:58:20 2014 -0800

    editor: add grid design to Builder style scheme
    
    Since we can't do this from the style scheme, we just add support for it
    in the GbSourceView. It means that other style schemes can't get support
    for it, but we'll fix that when we reach that. We can push the feature
    into GtkSourceView potentially. Might as well test it here first.

 src/editor/gb-source-view.c |   51 +++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)
---
diff --git a/src/editor/gb-source-view.c b/src/editor/gb-source-view.c
index 13849c9..ee1d651 100644
--- a/src/editor/gb-source-view.c
+++ b/src/editor/gb-source-view.c
@@ -1347,11 +1347,62 @@ gb_source_view_real_draw_layer (GbSourceView     *view,
                                 GtkTextViewLayer  layer,
                                 cairo_t          *cr)
 {
+  static GdkRGBA lines = { 0 };
   GbSourceViewPrivate *priv = view->priv;
+  GtkSourceStyleScheme *scheme;
   GtkTextView *text_view = GTK_TEXT_VIEW (view);
+  GtkTextBuffer *buffer;
 
   GTK_TEXT_VIEW_CLASS (gb_source_view_parent_class)->draw_layer (text_view, layer, cr);
 
+  if ((layer == GTK_TEXT_VIEW_LAYER_BELOW) &&
+      (buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view))) &&
+      GTK_SOURCE_IS_BUFFER (buffer) &&
+      (scheme = gtk_source_buffer_get_style_scheme (GTK_SOURCE_BUFFER (buffer))) &&
+      g_strcmp0 ("builder", gtk_source_style_scheme_get_id (scheme)) == 0)
+    {
+      GdkRectangle clip;
+      GdkRectangle vis;
+      gdouble x;
+      gdouble y;
+
+#define GRID_SIZE 16
+
+      if (lines.alpha == 0.0)
+        gdk_rgba_parse (&lines, "#eeefee");
+
+      cairo_save (cr);
+      cairo_set_line_width (cr, 1.0);
+      gdk_cairo_set_source_rgba (cr, &lines);
+      gdk_cairo_get_clip_rectangle (cr, &clip);
+      gtk_text_view_get_visible_rect (text_view, &vis);
+
+      /*
+       * The following constants come from gtktextview.c pixel cache
+       * settings. Sadly, I didn't expose those in public API so we have to
+       * just keep them in sync here. 64 for X, height/2 for Y.
+       */
+      x = (GRID_SIZE - (vis.x % GRID_SIZE)) - 64;
+      y = (GRID_SIZE - (vis.y % GRID_SIZE)) - (vis.height / 2 / GRID_SIZE * GRID_SIZE) - GRID_SIZE;
+
+      for (; x <= clip.x + clip.width; x += GRID_SIZE)
+        {
+          cairo_move_to (cr, x + .5, clip.y + .5);
+          cairo_line_to (cr, x + .5, clip.y + clip.height + .5);
+        }
+
+      for (; y <= clip.y + clip.height; y += GRID_SIZE)
+        {
+          cairo_move_to (cr, clip.x + .5, y + .5);
+          cairo_line_to (cr, clip.x + clip.width + .5, y + .5);
+        }
+
+      cairo_stroke (cr);
+      cairo_restore (cr);
+
+#undef GRID_SIZE
+    }
+
   if (layer == GTK_TEXT_VIEW_LAYER_BELOW)
     {
       if (priv->snippets->length)