fix division by zero mapbox#48

.travis.yml

@@ -19,7 +19,7 @@ addons:
     packages:
      - g++-4.9
      - gcc-4.9
-     - clang-3.7
+     - clang-3.8
      - cmake
      - cmake-data
      - xorg-dev
@@ -30,7 +30,7 @@ cache: apt
 
 before_script:
  - if [[ ${CXX} == "g++" ]]; then export CXX="g++-4.9" CC="gcc-4.9" ; fi
- - if [[ ${CXX} == "clang++" ]]; then export CXX="clang++-3.7" CC="clang-3.7" ; fi
+ - if [[ ${CXX} == "clang++" ]]; then export CXX="clang++-3.8" CC="clang-3.8" ; fi
 
 script:
  - mkdir ./build && cd ./build

CMakeLists.txt

@@ -7,7 +7,7 @@ option(EARCUT_BUILD_VIZ "Build the earcut visualizer program" ON)
 
 # configure optimization
 if (CMAKE_BUILD_TYPE STREQUAL "Debug")
-    set(OPTIMIZATION_FLAGS "-O0") # optional: -fsanitize=signed-integer-overflow,undefined
+    set(OPTIMIZATION_FLAGS "-O0 -fsanitize=undefined")
     set(IS_DEBUG true)
     message("-- Configuring debug build")
 else()

include/mapbox/earcut.hpp

@@ -464,7 +464,7 @@ Earcut<N>::findHoleBridge(Node* hole, Node* outerNode) {
     // find a segment intersected by a ray from the hole's leftmost Vertex to the left;
     // segment's endpoint with lesser x will be potential connection Vertex
     do {
-        if (hy <= p->y && hy >= p->next->y) {
+        if (hy <= p->y && hy >= p->next->y && p->next->y != p->y) {
           double x = p->x + (hy - p->y) * (p->next->x - p->x) / (p->next->y - p->y);
           if (x <= hx && x > qx) {
             qx = x;
@@ -495,7 +495,7 @@ Earcut<N>::findHoleBridge(Node* hole, Node* outerNode) {
     double my = m->y;
 
     while (p != stop) {
-        if (hx >= p->x && p->x >= mx &&
+        if (hx >= p->x && p->x >= mx && hx != p->x &&
             pointInTriangle(hy < my ? hx : qx, hy, mx, my, hy < my ? qx : hx, hy, p->x, p->y)) {
 
             tanCur = std::abs(hy - p->y) / (hx - p->x); // tangential
@@ -699,7 +699,8 @@ bool Earcut<N>::middleInside(const Node* a, const Node* b) {
     double px = (a->x + b->x) / 2;
     double py = (a->y + b->y) / 2;
     do {
-        if (((p->y > py) != (p->next->y > py)) && (px < (p->next->x - p->x) * (py - p->y) / (p->next->y - p->y) + p->x))
+        if (((p->y > py) != (p->next->y > py)) && p->next->y != p->y &&
+                (px < (p->next->x - p->x) * (py - p->y) / (p->next->y - p->y) + p->x))
             inside = !inside;
         p = p->next;
     } while (p != a);

test/test.cpp

@@ -70,8 +70,9 @@ void areaTest(const char *name, const Polygon &polygon, int expectedTriangles =
         const auto &indices = tesselator.indices();
 
         const auto area = trianglesArea(vertices, indices);
-        const double deviation =
-            (expectedArea == 0 && area == 0) ? 0 : std::abs(area - expectedArea) / expectedArea;
+        const double deviation = (expectedArea == area) ? 0 :
+                expectedArea == 0 ? std::numeric_limits<double>::infinity() :
+                std::abs(area - expectedArea) / expectedArea;
 
         t.ok(deviation <= earcutDeviation, std::string{ "earcut deviation " } + formatPercent(deviation) +
                                                 " is less than " +
@@ -91,8 +92,9 @@ void areaTest(const char *name, const Polygon &polygon, int expectedTriangles =
         const auto &indices = tesselator.indices();
 
         const auto area = trianglesArea(vertices, indices);
-        const double deviation =
-            (expectedArea == 0 && area == 0) ? 0 : std::abs(area - expectedArea) / expectedArea;
+        const double deviation = (expectedArea == area) ? 0 :
+                                 expectedArea == 0 ? std::numeric_limits<double>::infinity() :
+                                 std::abs(area - expectedArea) / expectedArea;
 
         t.ok(deviation <= libtess2Deviation, std::string{ "libtess2 deviation " } + formatPercent(deviation) +
                                                 " is less than " +