diff -r 06a1aef170aa -r 165777a20dc7 src/basics.h
--- a/src/basics.h	Thu Nov 05 14:29:58 2020 +0200
+++ b/src/basics.h	Sun Jan 10 15:28:44 2021 +0200
@@ -23,6 +23,7 @@
 #include <cstring>
 #include <cmath>
 #include <optional>
+#include <type_traits>
 #include <QMatrix4x4>
 #include <QObject>
 #include <QPointF>
@@ -162,9 +163,26 @@
 	return {point.x(), point.y()};
 }
 
-constexpr float PIf = static_cast<float>(M_PI);
-constexpr double PI = M_PI;
-constexpr long double PIl = M_PIl;
+/*
+ * coalesce(arg1, arg2, ..., argn)
+ * Returns the first of the given arguments that evaluates to true.
+ */
+template<typename T>
+T coalesce(T&& arg)
+{
+	// recursion base: 1 argument
+	return arg;
+}
+
+template<typename T, typename... Rest>
+std::common_type_t<T, Rest...> coalesce(T&& arg, Rest&&... rest)
+{
+	// general case: n arguments
+	return arg ? arg : coalesce(rest...);
+}
+
+template<typename T = double>
+constexpr std::enable_if_t<std::is_floating_point_v<T>, T> PI = static_cast<T>(M_PIl);
 
 Q_DECLARE_METATYPE(glm::vec3)
 Q_DECLARE_METATYPE(glm::mat4)