From 8a09bc4ae714d47bf539072b62724729f657c869 Mon Sep 17 00:00:00 2001
From: Bruno de Oliveira Abinader <bruno@mapbox.com>
Date: Thu, 19 Jul 2018 17:54:13 +0300
Subject: [core] Added mbgl::util::fuzzy{Compare,IsNull}

---
 cmake/core-files.cmake        |  1 +
 include/mbgl/math/compare.hpp | 36 ++++++++++++++++++++++++++++++++++++
 src/mbgl/util/tile_cover.cpp  |  7 +++++--
 3 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 include/mbgl/math/compare.hpp

diff --git a/cmake/core-files.cmake b/cmake/core-files.cmake
index 204bb78bce..e5ad757301 100644
--- a/cmake/core-files.cmake
+++ b/cmake/core-files.cmake
@@ -124,6 +124,7 @@ set(MBGL_CORE_FILES
     include/mbgl/math/log2.hpp
     include/mbgl/math/minmax.hpp
     include/mbgl/math/wrap.hpp
+    include/mbgl/math/compare.hpp
     src/mbgl/math/log2.cpp
 
     # parsedate
diff --git a/include/mbgl/math/compare.hpp b/include/mbgl/math/compare.hpp
new file mode 100644
index 0000000000..1a4c09c80a
--- /dev/null
+++ b/include/mbgl/math/compare.hpp
@@ -0,0 +1,36 @@
+#pragma once
+
+#include <cfloat>
+#include <cmath>
+
+namespace mbgl {
+namespace util {
+
+//template <typename T,
+//          typename = std::enable_if<std::is_floating_point<T>::value>>
+bool fuzzyEqual(double a, double b) {
+    double diff = ::fabs(a - b);
+    a = ::fabs(a);
+    b = ::fabs(b);
+    double min = b > a ? a : b;
+    return diff * 1e12 <= min;
+}
+
+bool fuzzyEqual(float a, float b) {
+    float diff = ::fabs(a - b);
+    a = ::fabs(a);
+    b = ::fabs(b);
+    float min = b > a ? a : b;
+    return diff * 1e5 <= min;
+}
+
+bool fuzzyIsNull(double a) {
+    return ::fabs(a) <= 1e-12;
+}
+
+bool fuzzyIsNull(float a) {
+    return ::fabs(a) <= 1e-5;
+}
+
+} // namespace util
+} // namespace mbgl
diff --git a/src/mbgl/util/tile_cover.cpp b/src/mbgl/util/tile_cover.cpp
index 00a261e083..dacd289d3a 100644
--- a/src/mbgl/util/tile_cover.cpp
+++ b/src/mbgl/util/tile_cover.cpp
@@ -4,6 +4,7 @@
 #include <mbgl/map/transform_state.hpp>
 #include <mbgl/util/tile_cover_impl.hpp>
 #include <mbgl/util/tile_coordinate.hpp>
+#include <mbgl/math/compare.hpp>
 
 #include <functional>
 #include <list>
@@ -34,7 +35,8 @@ struct edge {
 
 // scan-line conversion
 static void scanSpans(edge e0, edge e1, int32_t ymin, int32_t ymax, ScanLine scanLine) {
-    double y0 = util::max(double(ymin), std::floor(e1.y0));
+    bool fuzzyIsNull = util::fuzzyIsNull(e1.y0);
+    double y0 = util::max(double(ymin), fuzzyIsNull ? 0.0 : std::floor(e1.y0));
     double y1 = util::min(double(ymax), std::ceil(e1.y1));
 
     // sort edges by x-coordinate
@@ -52,7 +54,8 @@ static void scanSpans(edge e0, edge e1, int32_t ymin, int32_t ymax, ScanLine sca
     for (int32_t y = y0; y < y1; y++) {
         double x0 = m0 * util::max(0.0, util::min(e0.dy, y + d0 - e0.y0)) + e0.x0;
         double x1 = m1 * util::max(0.0, util::min(e1.dy, y + d1 - e1.y0)) + e1.x0;
-        scanLine(std::floor(x1), std::ceil(x0), y);
+        fuzzyIsNull = util::fuzzyIsNull(x1);
+        scanLine(fuzzyIsNull ? 0.0 : std::floor(x1), std::ceil(x0), y);
     }
 }
 
-- 
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