geom/segment: add trivial segment representation

CMakeLists.txt

@@ -244,6 +244,8 @@ list (
     geom/rect.hpp
     geom/sample.cpp
     geom/sample.hpp
+    geom/segment.cpp
+    geom/segment.hpp
     geom/sphere.cpp
     geom/sphere.hpp
     geom/tri.cpp
@@ -501,6 +503,7 @@ if (TESTS)
         geom/line
         geom/plane
         geom/ray
+        geom/segment
         geom/sphere
         hash/checksum
         hash/crc

geom/segment.cpp

@@ -0,0 +1,20 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "segment.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////

geom/segment.hpp

@@ -0,0 +1,58 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+#include "../point.hpp"
+
+
+namespace util::geom {
+    template <size_t S, typename T>
+    struct segment {
+        util::point<S,T> a;
+        util::point<S,T> b;
+    };
+
+
+    using segment2f = segment<2,float>;
+    using segment3f = segment<3,float>;
+
+
+    template <size_t S, typename T>
+    T
+    distance2 (segment<S,T> s, point<S,T> p)
+    {
+        const auto dir = s.b - s.a;
+        const auto t1 = dot (p - s.a, dir);
+        if (t1 < 0)
+            return distance2 (p, s.a);
+
+        const auto t2 = dot (dir, dir);
+        if (t2 < t1)
+            return distance2 (p, s.b);
+
+        auto t = t1 / t2;
+        return distance2 (p, s.a + t * dir);
+    }
+
+
+    template <size_t S, typename T>
+    T
+    distance (segment<S,T> s, point<S,T> p)
+    {
+        return std::sqrt (distance2 (s, p));
+    }
+};

test/geom/segment.cpp

@@ -0,0 +1,28 @@
+#include "tap.hpp"
+
+#include "geom/segment.hpp"
+
+int
+main (int, char**)
+{
+    util::TAP::logger tap;
+
+    static struct {
+        util::point3f a, b;
+        util::point3f q;
+        float distance;
+        const char *message;
+    } const TESTS[] = {
+        { { 0, 0, 0 }, { 1, 1, 1 }, { 0, 0, 0 }, 0, "origin line, origin point" },
+        { { 0, 0, 0 }, { 1, 1, 1 }, { 1, 1, 1 }, 0, "origin line, point on line" },
+        { { 0, 1, 0 }, { 1, 1, 0 }, { 0, 0, 0 }, 1, "+x line, unit distance" },
+    };
+
+    for (auto const& t: TESTS) {
+        util::geom::segment3f s {t.a, t.b};
+        auto d = distance (s, t.q);
+        tap.expect_eq (d, t.distance, "%!", t.message);
+    }
+
+    return tap.status ();
+}