core: enable sin in time_function model

Re-introduce the sin_time_function in kernel and GUI.
(closes: #39).
Co-authored-by: Yves Nedelec <yves.nedelec@cerema.fr>

app/gui/node-editor.cpp

@@ -2298,12 +2298,17 @@ show_dynamics_inputs(editor& /*ed*/, flow& /*dyn*/)
 static void
 show_dynamics_inputs(editor& /*ed*/, time_func& dyn)
 {
-    const char* items[] = { "time", "square" };
+    static const char* items[] = { "time", "square", "sin" };
+
     ImGui::PushItemWidth(120.0f);
-    int item_current = dyn.default_f == &time_function ? 0 : 1;
+    int item_current = dyn.default_f == &time_function          ? 0
+                       : dyn.default_f == &square_time_function ? 1
+                                                                : 2;
+
     if (ImGui::Combo("function", &item_current, items, IM_ARRAYSIZE(items))) {
-        dyn.default_f =
-          item_current == 0 ? &time_function : square_time_function;
+        dyn.default_f = item_current == 0   ? &time_function
+                        : item_current == 1 ? &square_time_function
+                                            : sin_time_function;
     }
     ImGui::PopItemWidth();
 }

lib/include/irritator/core.hpp

@@ -5643,9 +5643,18 @@ using qss3_cross = abstract_cross<3>;
 inline double
 sin_time_function(double t) noexcept
 {
-    const double f0 = 0.1;
-    const double pi = std::acos(-1);
-    return std::sin(2 * pi * f0 * t);
+    constexpr double f0 = 0.1;
+
+#if irt_have_numbers == 1
+    constexpr double pi = std::numbers::pi_v<double>;
+#else
+    // std::acos(-1) is not a constexpr in MVSC 2019
+    constexpr double pi = 3.141592653589793238462643383279502884;
+#endif
+
+    constexpr const double mult = 2.0 * pi * f0;
+
+    return std::sin(mult * t);
 }
 
 inline double

lib/include/irritator/io.hpp

@@ -1471,7 +1471,9 @@ private:
         if (!(is >> temp_1))
             return false;
 
-        if (std::strcmp(temp_1, "square") == 0)
+        if (std::strcmp(temp_1, "sin") == 0)
+            dyn.default_f = &sin_time_function;
+        else if (std::strcmp(temp_1, "square") == 0)
             dyn.default_f = &square_time_function;
         else
             dyn.default_f = &time_function;