Allow a theme to specify ellipsize width for a title

It's nice to indicate when a title is truncated with an ellipsis.
Because themes may draw a title multiple times to draw a shadow, or
may include the window icon within the title area, we can't determine
the proper ellipsization width automatically, so add an optional
attribute to the <title/> element "ellipsize_width" which, if set,
is the width to ellipsize at.

This is only enabled if a theme version of 3.1 is required.

When it's not set, we keep the old behavior of just letting the
title be clipped with a hard edge.

https://bugzilla.gnome.org/show_bug.cgi?id=591842

NOTE: Patch copied from mutter and adapted for metacity.

doc/theme-format.txt

@@ -32,6 +32,10 @@ Additional predefined variables are added for positioning expressions:
   frame_y_center: the Y center of the entire frame, with respect to the
       piece currently being drawn.
 
+The <title/> element now supports an "ellipsize_width" attribute. When
+specified, this gives a width at which to ellipsize the title. If not
+specified, the title will simply be clipped to the title area.
+
 New Features in Theme Format Version 3
 ======================================
 

src/ui/frames.c

@@ -482,6 +482,7 @@ meta_frames_ensure_layout (MetaFrames  *frames,
 
       frame->layout = gtk_widget_create_pango_layout (widget, frame->title);
 
+      pango_layout_set_ellipsize (frame->layout, PANGO_ELLIPSIZE_END);
       pango_layout_set_auto_dir (frame->layout, FALSE);
 
       pango_layout_set_single_paragraph_mode (frame->layout, TRUE);

src/ui/theme-parser.c

@@ -2615,12 +2615,14 @@ parse_draw_op_element (GMarkupParseContext  *context,
       const char *color;
       const char *x;
       const char *y;
+      const char *ellipsize_width;
       MetaColorSpec *color_spec;
 
       if (!locate_attributes (context, element_name, attribute_names, attribute_values,
                               error,
                               "!color", &color,
                               "!x", &x, "!y", &y,
+                              "ellipsize_width", &ellipsize_width,
                               NULL))
         return;
 
@@ -2630,8 +2632,18 @@ parse_draw_op_element (GMarkupParseContext  *context,
 
       if (!check_expression (y, FALSE, info->theme, context, error))
         return;
+
+      if (!check_expression (ellipsize_width, FALSE, info->theme, context, error))
+        return;
 #endif
 
+      if (ellipsize_width && peek_required_version (info) < 3001)
+        {
+          set_error (error, context, G_MARKUP_ERROR, G_MARKUP_ERROR_PARSE,
+                     ATTRIBUTE_NOT_FOUND, "ellipsize_width", element_name);
+          return;
+        }
+
       /* Check last so we don't have to free it when other
        * stuff fails
        */
@@ -2648,6 +2660,8 @@ parse_draw_op_element (GMarkupParseContext  *context,
 
       op->data.title.x = meta_draw_spec_new (info->theme, x, NULL);
       op->data.title.y = meta_draw_spec_new (info->theme, y, NULL);
+      if (ellipsize_width)
+        op->data.title.ellipsize_width = meta_draw_spec_new (info->theme, ellipsize_width, NULL);
 
       g_assert (info->op_list);
 

src/ui/theme.c

@@ -3010,6 +3010,8 @@ meta_draw_op_free (MetaDrawOp *op)
 
       meta_draw_spec_free (op->data.title.x);
       meta_draw_spec_free (op->data.title.y);
+      if (op->data.title.ellipsize_width)
+        meta_draw_spec_free (op->data.title.ellipsize_width);
       break;
 
     case META_DRAW_OP_LIST:
@@ -3875,14 +3877,47 @@ meta_draw_op_draw_with_env (const MetaDrawOp    *op,
       if (info->title_layout)
         {
           int rx, ry;
+          PangoRectangle ink_rect, logical_rect;
 
           meta_color_spec_render (op->data.title.color_spec, style_gtk, &color);
           gdk_cairo_set_source_rgba (cr, &color);
 
           rx = parse_x_position_unchecked (op->data.title.x, env);
           ry = parse_y_position_unchecked (op->data.title.y, env);
 
-          if (rx - env->rect.x + env->title_width >= env->rect.width)
+          if (op->data.title.ellipsize_width)
+            {
+              int ellipsize_width;
+              int right_bearing;
+
+              ellipsize_width = parse_x_position_unchecked (op->data.title.ellipsize_width, env);
+              /* HACK: parse_x_position_unchecked adds in env->rect.x, subtract out again */
+              ellipsize_width -= env->rect.x;
+
+              pango_layout_set_width (info->title_layout, -1);
+              pango_layout_get_pixel_extents (info->title_layout,
+                                              &ink_rect, &logical_rect);
+
+              /* Pango's idea of ellipsization is with respect to the logical rect.
+               * correct for this, by reducing the ellipsization width by the overflow
+               * of the un-ellipsized text on the right... it's always the visual
+               * right we want regardless of bidi, since since the X we pass in to
+               * cairo_move_to() is always the left edge of the line.
+               */
+              right_bearing = (ink_rect.x + ink_rect.width) - (logical_rect.x + logical_rect.width);
+              right_bearing = MAX (right_bearing, 0);
+
+              ellipsize_width -= right_bearing;
+              ellipsize_width = MAX (ellipsize_width, 0);
+
+              /* Only ellipsizing when necessary is a performance optimization -
+               * pango_layout_set_width() will force a relayout if it isn't the
+               * same as the current width of -1.
+               */
+              if (ellipsize_width < logical_rect.width)
+                pango_layout_set_width (info->title_layout, PANGO_SCALE * ellipsize_width);
+            }
+          else if (rx - env->rect.x + env->title_width >= env->rect.width)
           {
             const double alpha_margin = 30.0;
             int text_space = env->rect.x + env->rect.width -
@@ -3907,12 +3942,14 @@ meta_draw_op_draw_with_env (const MetaDrawOp    *op,
                                                           color.blue, 0);
             cairo_set_source(cr, linpat);
             cairo_pattern_destroy(linpat);
-          } else {
-            gdk_cairo_set_source_rgba (cr, &color);
           }
 
           cairo_move_to (cr, rx, ry);
           pango_cairo_show_layout (cr, info->title_layout);
+
+          /* Remove any ellipsization we might have set; will short-circuit
+           * if the width is already -1 */
+          pango_layout_set_width (info->title_layout, -1);
         }
       break;
 

src/ui/theme.h

@@ -539,6 +539,7 @@ struct _MetaDrawOp
       MetaColorSpec *color_spec;
       MetaDrawSpec *x;
       MetaDrawSpec *y;
+      MetaDrawSpec *ellipsize_width;
     } title;
 
     struct {