triangle plane intersection tests

typed-geometry @ f98a78e6

-Subproject commit f0136489a98723376f10be4ab1ff8e9bae146b6a
+Subproject commit f98a78e690b49be701eb4dd6f6415e8c697130fd

tests/feature/intersections/plane-intersect.cc

@@ -197,4 +197,67 @@ TG_FUZZ_TEST(Plane, Intersect)
             CHECK(intersects(c, p));
         }
     }
+
+    // plane3 - triangle3
+    {
+        auto const box = tg::aabb3(tg::pos3(-10.0f), tg::pos3(10.0f));
+        auto const center = uniform(rng, box);
+        auto const n = tg::uniform<tg::dir3>(rng);
+        auto plane = tg::plane3(n, center);
+
+        auto const t = any_normal(n);
+        auto const bi = normalize(cross(n, t));
+
+        // coplanar triangle
+        auto triangle = tg::triangle3(center, center + t, center + bi);
+        CHECK(intersects(triangle, plane));
+
+        // one point of triangle in plane
+        tg::array<tg::pos3, 3> c = {center, center + n, center + n + t};
+        // check all possible orders
+        for (auto i = 0; i < 3; i++)
+        {
+            triangle = tg::triangle(c[(i + 0) % 3], c[(i + 1) % 3], c[(i + 2) % 3]);
+            CHECK(intersects(plane, triangle));
+
+            triangle = tg::triangle(c[(i + 1) % 3], c[(i + 0) % 3], c[(i + 2) % 3]);
+            CHECK(intersects(plane, triangle));
+        }
+
+        // all above triangle in plane
+        c = {center + n + bi, center + n, center + n + t};
+        // check all possible orders
+        for (auto i = 0; i < 3; i++)
+        {
+            triangle = tg::triangle(c[(i + 0) % 3], c[(i + 1) % 3], c[(i + 2) % 3]);
+            CHECK(!intersects(plane, triangle));
+
+            triangle = tg::triangle(c[(i + 1) % 3], c[(i + 0) % 3], c[(i + 2) % 3]);
+            CHECK(!intersects(plane, triangle));
+        }
+
+        // all below triangle in plane
+        c = {center - n + bi, center - n, center - n + t};
+        // check all possible orders
+        for (auto i = 0; i < 3; i++)
+        {
+            triangle = tg::triangle(c[(i + 0) % 3], c[(i + 1) % 3], c[(i + 2) % 3]);
+            CHECK(!intersects(plane, triangle));
+
+            triangle = tg::triangle(c[(i + 1) % 3], c[(i + 0) % 3], c[(i + 2) % 3]);
+            CHECK(!intersects(plane, triangle));
+        }
+
+        // 2 on 1 side
+        c = {center - n + bi, center + n, center - n + t};
+        // check all possible orders
+        for (auto i = 0; i < 3; i++)
+        {
+            triangle = tg::triangle(c[(i + 0) % 3], c[(i + 1) % 3], c[(i + 2) % 3]);
+            CHECK(intersects(plane, triangle));
+
+            triangle = tg::triangle(c[(i + 1) % 3], c[(i + 0) % 3], c[(i + 2) % 3]);
+            CHECK(intersects(plane, triangle));
+        }
+    }
 }