From patchwork Thu Apr 16 12:04:21 2015
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Subject: [RFC] mi: reduce missing segments on large ellipse
From: Olivier Fourdan <ofourdan@redhat.com>
X-Patchwork-Id: 47327
Message-Id: <1429185861-4411-2-git-send-email-ofourdan@redhat.com>
To: xorg-devel@lists.x.org
Cc: Olivier Fourdan <ofourdan@redhat.com>
Date: Thu, 16 Apr 2015 14:04:21 +0200

With larger ellipses, rounding will cause some spans close to vertical
tangent to be of zero length, leading to sometimes rather large missing
portion of the arc.

Try to detect this case and work around it.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1166989
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91858
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
---
 mi/miarc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mi/miarc.c b/mi/miarc.c
index e8bc87e..be9c94c 100644
--- a/mi/miarc.c
+++ b/mi/miarc.c
@@ -563,6 +563,16 @@ miComputeEllipseSpans(int lw, xArc * parc, miArcSpanData * spdata)
                     outx = x + t;
             }
         }
+        if (ICEIL(xorg + outx) - ICEIL(xorg + inx) < lw ) {
+            if (inx <= 0.0) {
+                outx = outx + ICEIL(-r);
+                inx = inx + ICEIL(r);
+	    }
+	    else {
+                outx = outx + ICEIL(r);
+                inx = inx + ICEIL(-r);
+	    }
+        }
         span->lx = ICEIL(xorg - outx);
         if (inx <= 0.0) {
             spdata->count1++;