Clean up antialiasing fixes

Simplify the code by noting that when we have square end-caps, the
results of generic line path give the right pixel-aligned rectangle
for horizontal/vertical lines.

Add comments and remove some extra braces.

https://bugzilla.gnome.org/show_bug.cgi?id=630426

1 files changed, 11 insertions, 24 deletions

diff --git a/src/ui/theme.c b/src/ui/theme.c
index e348f62e..b5b6308e 100644
--- a/src/ui/theme.c
+++ b/src/ui/theme.c
@@ -3758,44 +3758,31 @@ meta_draw_op_draw_with_env (const MetaDrawOp    *op,
               y2 = y1;
 
             /* This is one of the cases where we are matching the exact
-             * pixel aligned rectangle produced by X.
+             * pixel aligned rectangle produced by X; for zero-width lines
+             * the generic algorithm produces the right result so we don't
+             * need to handle them here.
              */
-            if (y1 == y2 || x1 == x2)
+            if ((y1 == y2 || x1 == x2) && op->data.line.width != 0)
               {
-                double offset = (op->data.line.width == 0 ||
-                                 op->data.line.width % 2) ? .5 : 0;
-                /* X includes end points for lines of width 0 */
-                double line_extend = op->data.line.width == 0 ? 1. : 0.;
+                double offset = op->data.line.width % 2 ? .5 : 0;
 
                 if (y1 == y2)
                   {
-                    if (x2 < x1)
-                    {
-                       x1 ^= x2;
-                       x2 ^= x1;
-                       x1 ^= x2;
-                    }
                     cairo_move_to (cr, x1, y1 + offset);
-                    cairo_line_to (cr, x2 + line_extend, y2 + offset);
+                    cairo_line_to (cr, x2, y2 + offset);
                   }
                 else
                   {
-                    if (y2 < y1)
-                    {
-                      y1 ^= y2;
-                      y2 ^= y1;
-                      y1 ^= y2;
-                    }
                     cairo_move_to (cr, x1 + offset, y1);
-                    cairo_line_to (cr, x2 + offset, y2 + line_extend);
+                    cairo_line_to (cr, x2 + offset, y2);
                   }
               }
             else
               {
-                if (op->data.line.width <= 0)
-                  {
-                    cairo_set_line_cap (cr, CAIRO_LINE_CAP_SQUARE);
-                  }
+                /* zero-width lines include both end-points in X, unlike wide lines */
+                if (op->data.line.width == 0)
+                  cairo_set_line_cap (cr, CAIRO_LINE_CAP_SQUARE);
+
                 cairo_move_to (cr, x1 + .5, y1 + .5);
                 cairo_line_to (cr, x2 + .5, y2 + .5);
               }