Plot3D

# include <Siv3D.hpp>

void Plot3D(const ParsedExpression& f, MeshData& meshData)
{
    for (auto& v : meshData.vertices)
    {
        v.position.y = static_cast<float>(f.evaluateOpt({
                { L"x", v.position.x }, { L"y", v.position.z } }).value_or(0.0));
    }

    meshData.computeNormals();
}

void Main()
{
    Graphics::SetBackground(Color(120, 180, 160));

    const String defaultExpression = L"5 * sin(sqrt(x^2+y^2)+0.0001) / (sqrt(x^2+y^2)+0.0001)";
    MeshData meshData = MeshData::Grid(25, 100);
    Plot3D(ParsedExpression(defaultExpression), meshData);
    DynamicMesh mesh(meshData);

    GUI gui(GUIStyle::Default);
    gui.addln(L"exp", GUITextArea::Create(2, 32));
    gui.add(L"grid", GUIToggleSwitch::Create(L"グリッド非表示", L"グリッド表示", false));
    gui.textArea(L"exp").setText(defaultExpression);

    while (System::Update())
    {
        if (!gui.textArea(L"exp").active)
        {
            Graphics3D::FreeCamera();
        }

        if (gui.textArea(L"exp").hasChanged)
        {
            if (const ParsedExpression exp{ gui.textArea(L"exp").text })
            {
                gui.textArea(L"exp").style.color = Palette::Black;
                Plot3D(exp, meshData);
                mesh.fillVertices(meshData.vertices);
            }
            else
            {
                gui.textArea(L"exp").style.color = Palette::Red;
            }
        }

        if (mesh)
        {
            if (gui.toggleSwitch(L"grid").isRight)
            {
                RasterizerState raster = RasterizerState::WireframeCullBack;
                raster.depthBias = 10000;
                Graphics3D::SetRasterizerState(raster);

                mesh.draw(Palette::Black);

                Graphics3D::SetRasterizerState(RasterizerState::Default3D);
            }

            mesh.draw();
        }
    }
}