[glabels] Workaround for pango kerning bug.

[Jim Evins <jimevins src gnome org>]

commit acb8a0c8e4ee4131b059aeb4544c4ef108dd183c
Author: Jim Evins <evins snaught com>
Date:   Sun Jun 16 00:28:45 2013 -0400

    Workaround for pango kerning bug.
    
    Fixes bug #698777.  This is a workaround for pango-cairo bug #700592, which is
    a regression of bug #341481 which was originally fixed back in 2009.  This
    workaround works by rendering the font at device scale rather than world scale.
    To make this work the actual font size is manually scaled appropriately to
    compensate for this.

 src/label-text.c |   23 +++++++++++++++++------
 1 files changed, 17 insertions(+), 6 deletions(-)
---
diff --git a/src/label-text.c b/src/label-text.c
index 3f0305f..287d3cc 100644
--- a/src/label-text.c
+++ b/src/label-text.c
@@ -1115,13 +1115,24 @@ set_text_path (glLabelText      *this,
         PangoLayout          *layout;
         PangoStyle            style;
         PangoFontDescription *desc;
+        gdouble               scale_x, scale_y;
         cairo_font_options_t *font_options;
         PangoContext         *context;
 
 
         gl_debug (DEBUG_LABEL, "START");
 
+        /*
+         * Workaround for pango Bug#700592, which is a regression of Bug#341481.
+         * Render font at device scale and scale font size accordingly.
+         */
+        scale_x = 1.0;
+        scale_y = 1.0;
+        cairo_device_to_user_distance (cr, &scale_x, &scale_y);
+        scale_x = fabs (scale_x);
+        scale_y = fabs (scale_y);
         cairo_save (cr);
+        cairo_scale (cr, scale_x, scale_y);
 
         gl_label_object_get_size (GL_LABEL_OBJECT (this), &object_w, &object_h);
         gl_label_object_get_raw_size (GL_LABEL_OBJECT (this), &raw_w, &raw_h);
@@ -1159,20 +1170,20 @@ set_text_path (glLabelText      *this,
         desc = pango_font_description_new ();
         pango_font_description_set_family (desc, this->priv->font_family);
         pango_font_description_set_weight (desc, this->priv->font_weight);
-        pango_font_description_set_size   (desc, font_size * PANGO_SCALE);
+        pango_font_description_set_size   (desc, font_size * PANGO_SCALE / scale_x);
         pango_font_description_set_style  (desc, style);
         pango_layout_set_font_description (layout, desc);
         pango_font_description_free       (desc);
 
         pango_layout_set_text (layout, text, -1);
-        pango_layout_set_spacing (layout, font_size * (this->priv->line_spacing-1) * PANGO_SCALE);
+        pango_layout_set_spacing (layout, font_size * (this->priv->line_spacing-1) * PANGO_SCALE / scale_x);
         if (raw_w == 0.0)
         {
                 pango_layout_set_width (layout, -1);
         }
         else
         {
-                pango_layout_set_width (layout, object_w * PANGO_SCALE);
+                pango_layout_set_width (layout, object_w * PANGO_SCALE / scale_x);
         }
         pango_layout_set_wrap (layout, PANGO_WRAP_WORD);
         pango_layout_set_alignment (layout, this->priv->align);
@@ -1181,17 +1192,17 @@ set_text_path (glLabelText      *this,
         switch (this->priv->valign)
         {
         case GL_VALIGN_VCENTER:
-                y = (object_h - ih) / 2;
+                y = (object_h/scale_x - ih) / 2;
                 break;
         case GL_VALIGN_BOTTOM:
-                y = object_h - ih;
+                y = object_h/scale_x - ih;
                 break;
         default:
                 y = 0;
                 break;
         }
 
-        cairo_move_to (cr, GL_LABEL_TEXT_MARGIN, y);
+        cairo_move_to (cr, GL_LABEL_TEXT_MARGIN/scale_x, y);
         pango_cairo_layout_path (cr, layout);
 
         g_object_unref (layout);