From bd71eb8681529ab70ff892b12128f8b7a5faa4c7 Mon Sep 17 00:00:00 2001
From: "Thiago Marcos P. Santos" <thiago@mapbox.com>
Date: Mon, 16 Jan 2017 17:43:33 +0200
Subject: [PATCH] [core] Fix ambiguous condition on the sort criteria

The previous sorting criteria would sometimes allow

C > B, B > A but A > C, making the internal std::sort
code sometimes point to an invalid reference.

Fixes #7737
---
 src/mbgl/style/style.cpp | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/mbgl/style/style.cpp b/src/mbgl/style/style.cpp
index 2d11d16b1..0b516f7b9 100644
--- a/src/mbgl/style/style.cpp
+++ b/src/mbgl/style/style.cpp
@@ -26,8 +26,10 @@
 #include <mbgl/renderer/render_item.hpp>
 #include <mbgl/renderer/render_tile.hpp>
 #include <mbgl/util/constants.hpp>
+#include <mbgl/util/geometry.hpp>
 #include <mbgl/util/string.hpp>
 #include <mbgl/util/logging.hpp>
+#include <mbgl/util/math.hpp>
 #include <mbgl/math/minmax.hpp>
 
 #include <algorithm>
@@ -409,9 +411,6 @@ RenderData Style::getRenderData(MapDebugOptions debugOptions, float angle) const
         }
     }
 
-    const bool isLeft = std::abs(angle) > M_PI_2;
-    const bool isBottom = angle < 0;
-
     for (const auto& layer : layers) {
         if (!layer->baseImpl->needsRendering(zoomHistory.lastZoom)) {
             continue;
@@ -456,13 +455,14 @@ RenderData Style::getRenderData(MapDebugOptions debugOptions, float angle) const
                 [](auto& pair) { return std::ref(pair.second); });
         if (symbolLayer) {
             std::sort(sortedTiles.begin(), sortedTiles.end(),
-                      [isLeft, isBottom](const RenderTile& a, const RenderTile& b) {
-                bool sortX = a.id.canonical.x > b.id.canonical.x;
-                bool sortW = a.id.wrap > b.id.wrap;
-                bool sortY = a.id.canonical.y > b.id.canonical.y;
-                return
-                    a.id.canonical.y != b.id.canonical.y ? (isLeft ? sortY : !sortY) :
-                    a.id.wrap != b.id.wrap ? (isBottom ? sortW : !sortW) : (isBottom ? sortX : !sortX);
+                      [angle](const RenderTile& a, const RenderTile& b) {
+                Point<float> pa(a.id.canonical.x, a.id.canonical.y);
+                Point<float> pb(b.id.canonical.x, b.id.canonical.y);
+
+                auto par = util::rotate(pa, angle);
+                auto pbr = util::rotate(pb, angle);
+
+                return std::tie(par.y, par.x) < std::tie(pbr.y, pbr.x);
             });
         }