From 8cfbdf2f02ba01d5638a91c9f3f7fc228b402caa Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 8 Feb 2013 13:10:25 +0000
Subject: [PATCH] polygon: Only rely on the computed boundary intersections for
 crossing edges

If we need to extrapolate the edge to the boundary, then we run the risk
of an overflow for an immaterial result. So if the edge does not cross
the boundary, we can simply use the corresponding end-point and not emit
the boundary segment.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=60489
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 src/cairo-polygon.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/src/cairo-polygon.c b/src/cairo-polygon.c
index c714b32ad..4c5861df4 100644
--- a/src/cairo-polygon.c
+++ b/src/cairo-polygon.c
@@ -420,11 +420,14 @@ _add_clipped_edge (cairo_polygon_t *polygon,
 	     * inside the box if it is clipped to this vertical range.
 	     */
 
-	    top_left_to_bottom_right = (p1->x < p2->x) == (p1->y < p2->y);
-
+	    top_left_to_bottom_right = (p1->x <= p2->x) == (p1->y <= p2->y);
 	    if (top_left_to_bottom_right) {
-		if (_cairo_edge_compute_intersection_x_for_y (p1, p2, left_y) < limits->p1.x)
-		    left_y++;
+		if (pleft >= limits->p1.x) {
+		    left_y = top_y;
+		} else {
+		    if (_cairo_edge_compute_intersection_x_for_y (p1, p2, left_y) < limits->p1.x)
+			left_y++;
+		}
 
 		left_y = MIN (left_y, bot_y);
 		if (top_y < left_y) {
@@ -434,8 +437,12 @@ _add_clipped_edge (cairo_polygon_t *polygon,
 		    top_y = left_y;
 		}
 
-		if (_cairo_edge_compute_intersection_x_for_y (p1, p2, right_y) > limits->p1.y)
-		    right_y--;
+		if (pright <= limits->p2.x) {
+		    right_y = bot_y;
+		} else {
+		    if (_cairo_edge_compute_intersection_x_for_y (p1, p2, right_y) > limits->p2.x)
+			right_y--;
+		}
 
 		right_y = MAX (right_y, top_y);
 		if (bot_y > right_y) {
@@ -445,8 +452,12 @@ _add_clipped_edge (cairo_polygon_t *polygon,
 		    bot_y = right_y;
 		}
 	    } else {
-		if (_cairo_edge_compute_intersection_x_for_y (p1, p2, right_y) > limits->p2.x)
-		    right_y++;
+		if (pright <= limits->p2.x) {
+		    right_y = top_y;
+		} else {
+		    if (_cairo_edge_compute_intersection_x_for_y (p1, p2, right_y) > limits->p2.x)
+			right_y++;
+		}
 
 		right_y = MIN (right_y, bot_y);
 		if (top_y < right_y) {
@@ -456,8 +467,12 @@ _add_clipped_edge (cairo_polygon_t *polygon,
 		    top_y = right_y;
 		}
 
-		if (_cairo_edge_compute_intersection_x_for_y (p1, p2, left_y) < limits->p1.x)
-		    left_y--;
+		if (pleft >= limits->p1.x) {
+		    left_y = bot_y;
+		} else {
+		    if (_cairo_edge_compute_intersection_x_for_y (p1, p2, left_y) < limits->p1.x)
+			left_y--;
+		}
 
 		left_y = MAX (left_y, top_y);
 		if (bot_y > left_y) {