LibDraw: Add beginnings of a triangle class

Currently the points of a triangle do not need to be initialised in a
certain orientation. Currently, the only real method in the class is
`contains`. However we can continue extending the class if and when we
need more functionality.

1 files changed, 77 insertions, 0 deletions

diff --git a/Libraries/LibDraw/Triangle.h b/Libraries/LibDraw/Triangle.h
new file mode 100644
index 0000000000..9afb7da1f6
--- /dev/null
+++ b/Libraries/LibDraw/Triangle.h
@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2020, Shannon Booth <shannon.ml.booth@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibDraw/Point.h>
+
+class Triangle {
+public:
+    Triangle(Point a, Point b, Point c)
+        : m_a(a)
+        , m_b(b)
+        , m_c(c)
+    {
+        m_det = (m_b.x() - m_a.x()) * (m_c.y() - m_a.y()) - (m_b.y() - m_a.y()) * (m_c.x() - m_a.x());
+    }
+
+    Point a() const { return m_a; }
+    Point b() const { return m_b; }
+    Point c() const { return m_c; }
+
+    bool contains(Point p) const
+    {
+        int x = p.x();
+        int y = p.y();
+
+        int ax = m_a.x();
+        int bx = m_b.x();
+        int cx = m_c.x();
+
+        int ay = m_a.y();
+        int by = m_b.y();
+        int cy = m_c.y();
+
+        if (m_det * ((bx - ax) * (y - ay) - (by - ay) * (x - ax)) <= 0)
+            return false;
+        if (m_det * ((cx - bx) * (y - by) - (cy - by) * (x - bx)) <= 0)
+            return false;
+        if (m_det * ((ax - cx) * (y - cy) - (ay - cy) * (x - cx)) <= 0)
+            return false;
+        return true;
+    }
+
+    String to_string() const { return String::format("(%s,%s,%s)", m_a.to_string().characters(), m_b.to_string().characters(), m_c.to_string().characters()); }
+
+private:
+    int m_det;
+    Point m_a;
+    Point m_b;
+    Point m_c;
+};
+
+inline const LogStream& operator<<(const LogStream& stream, const Triangle& value)
+{
+    return stream << value.to_string();
+}