[vte/wip/mosaic: 7/8] draw: Improve diagnoals drawing

[Christian Persch <chpe src gnome org>]

commit 2a56b742910ddad2eaea76424b7894168dc1d787
Author: Christian Persch <chpe src gnome org>
Date:   Thu Nov 14 23:09:22 2019 +0100

    draw: Improve diagnoals drawing
    
    Make the diagonals contiguous by allowing them to slightly extend
    outside the cell on the left and right.

 src/vtedraw.cc | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)
---
diff --git a/src/vtedraw.cc b/src/vtedraw.cc
index 9fad9495..2a10c4e9 100644
--- a/src/vtedraw.cc
+++ b/src/vtedraw.cc
@@ -1499,17 +1499,19 @@ _vte_draw_terminal_draw_graphic(struct _vte_draw *draw,
         case 0x2572: /* box drawings light diagonal upper left to lower right */
         case 0x2573: /* box drawings light diagonal cross */
         {
-                cairo_set_line_cap(cr, CAIRO_LINE_CAP_ROUND);
+                auto const dx = (light_line_width + 1) / 2;
+                cairo_rectangle(cr, x - dx, y, width + 2 * dx, height);
+                cairo_clip(cr);
+                cairo_set_line_cap(cr, CAIRO_LINE_CAP_SQUARE);
                 cairo_set_line_width(cr, light_line_width);
-                adjust = light_line_width / 2.;
                 if (c != 0x2571) {
-                        cairo_move_to(cr, x + adjust, y + adjust);
-                        cairo_line_to(cr, xright - adjust, ybottom - adjust);
+                        cairo_move_to(cr, x, y);
+                        cairo_line_to(cr, xright, ybottom);
                         cairo_stroke(cr);
                 }
                 if (c != 0x2572) {
-                        cairo_move_to(cr, xright - adjust, y + adjust);
-                        cairo_line_to(cr, x + adjust, ybottom - adjust);
+                        cairo_move_to(cr, xright, y);
+                        cairo_line_to(cr, x, ybottom);
                         cairo_stroke(cr);
                 }
                 break;