[pango/visible-things] cairo: Render tabs

[Matthias Clasen <matthiasc src gnome org>]

commit 653f1018b866d44d976683fb2631b68352aeb703
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Jul 7 16:45:23 2019 -0400

    cairo: Render tabs
    
    When we meet an unknown glyph for 0x09, render
    an arrow to indicate a tab.

 pango/pangocairo-render.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
---
diff --git a/pango/pangocairo-render.c b/pango/pangocairo-render.c
index e87ad4f4..c18556c8 100644
--- a/pango/pangocairo-render.c
+++ b/pango/pangocairo-render.c
@@ -405,6 +405,31 @@ _pango_cairo_renderer_draw_unknown_glyph (PangoCairoRenderer *crenderer,
       cairo_fill (crenderer->cr);
       goto done;
     }
+  else if (ch == '\t')
+    {
+      double y = cy + hbi->box_descent - 0.5 * hbi->box_height;
+      double width = (double)gi->geometry.width / PANGO_SCALE;
+      double arrow_offset = 0.2 * width;
+      double x = cx + arrow_offset;
+      double arrow_length = width - 2 * arrow_offset;
+      double tip_length = MIN (hbi->digit_width, 0.75 * arrow_length);
+      double tip_width = 3 * hbi->line_width;
+
+      cairo_move_to (crenderer->cr, x - 0.5 * hbi->line_width, y - 0.5 * tip_width);
+      cairo_line_to (crenderer->cr, x + 0.5 * hbi->line_width, y - 0.5 * tip_width);
+      cairo_line_to (crenderer->cr, x + 0.5 * hbi->line_width, y - 0.5 * hbi->line_width);
+      cairo_line_to (crenderer->cr, x + arrow_length - tip_length, y - 0.5 * hbi->line_width);
+      cairo_line_to (crenderer->cr, x + arrow_length - tip_length, y - 0.5 * tip_width); 
+      cairo_line_to (crenderer->cr, x + arrow_length,  y);
+      cairo_line_to (crenderer->cr, x + arrow_length - tip_length, y + 0.5 * tip_width); 
+      cairo_line_to (crenderer->cr, x + arrow_length - tip_length, y + 0.5 * hbi->line_width);
+      cairo_line_to (crenderer->cr, x + 0.5 * hbi->line_width, y + 0.5 * hbi->line_width);
+      cairo_line_to (crenderer->cr, x + 0.5 * hbi->line_width, y + 0.5 * tip_width);
+      cairo_line_to (crenderer->cr, x - 0.5 * hbi->line_width, y + 0.5 * tip_width);
+      cairo_close_path (crenderer->cr);
+      cairo_fill (crenderer->cr);
+      goto done;
+    }
   else if ((name = pango_get_ignorable_size (ch, &rows, &cols)))
     {
       /* nothing else to do */