Plot 3D surfaces

public partial class Plot3DMainForm : Form
{
    Surface3DRenderer sr;

    double x, y, z; // observer coordinates

    public Plot3DMainForm()
    {
        InitializeComponent();
        sr = new Surface3DRenderer(x, y, z, 0, 0, ClientRectangle.Width, ClientRectangle.Height- groupBox1.Height, 0.5, 0, 0);
        sr.ColorSchema = new ColorSchema(tbHue.Value);
        sr.SetFunction("sin(x1)*cos(x2)/(sqrt(sqrt(x1*x1+x2*x2))+1)*10");
        Form1_Resize(null, null);
        ResizeRedraw = true;
        DoubleBuffered = true;
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        e.Graphics.Clear(BackColor);
        sr.RenderSurface(e.Graphics);
    }

    private void Form1_Resize(object sender, EventArgs e)
    {
        refresh();
    }

    private void tbHue_Scroll(object sender, EventArgs e)
    {
        sr.ColorSchema = new ColorSchema(tbHue.Value);
        this.Invalidate();
    }

    private void trackBar1_Scroll(object sender, EventArgs e)
    {
        refresh();
    }

    private void trackBar2_Scroll(object sender, EventArgs e)
    {
        refresh();
    }

    private void trackBar3_Scroll(object sender, EventArgs e)
    {
        refresh();
    }

    private void refresh()
    {
        // three sliders are inputs in spherical coordinats
        double rho = (double)trackBar1.Value; // range 10..500, default 200
        double theta = (double)trackBar2.Value * Math.PI / 180.0; // range 0..360
        double phi = (double)trackBar3.Value * Math.PI / 180.0; // range 0..360

        // convert those coordinates to a rectangular form
        x = rho * Math.Sin(theta) * Math.Cos(phi);
        y = rho * Math.Sin(theta) * Math.Sin(phi);
        z = rho * Math.Cos(theta);

        sr.ReCalculateTransformationsCoeficients(x, y, z, 0, 0, ClientRectangle.Width, ClientRectangle.Height - groupBox1.Height, 0.5, 0, 0);
        this.Invalidate();
    }
}

public partial class Plot3DMainForm : Form {
    Surface3DRenderer sr;

    Boolean isMouseLeftButtonDown = false;
    Boolean isMouseRightButtonDown = false;
    Boolean isShiftDown = false;

    double zoom = 0.5;
    Point mouseLocation;
    Point screenXY = new Point(0, 0);
    Point3D observableXYZ = new Point3D(70, 35, 40);
        
    public Plot3DMainForm() {
        InitializeComponent();
        sr = new Surface3DRenderer(observableXYZ.x, observableXYZ.y, observableXYZ.z, screenXY.X, screenXY.Y, ClientRectangle.Width, ClientRectangle.Height, zoom, 0, 0);
        sr.ColorSchema = new ColorSchema(tbHue.Value);
        sr.SetFunction("sin(x1)*cos(x2)/(sqrt(sqrt(x1*x1+x2*x2))+1)*10");
        ResizeRedraw = true;
        DoubleBuffered = true;

        this.KeyPreview=true;

        ReCalculateTransformations();

        this.Resize += (s, e) => { ReCalculateTransformations(); };
        this.Paint += (s, e) => {
            e.Graphics.Clear(BackColor);
            sr.RenderSurface(e.Graphics);
        };

        this.KeyDown += (s, e) => { isShiftDown = e.Shift; this.Text = isShiftDown.ToString(); };
        this.KeyUp += (s, e) => { isShiftDown = e.Shift; this.Text = isShiftDown.ToString(); };

        this.MouseDown += (s, e) => {
            mouseLocation = e.Location;

            if(e.Button == MouseButtons.Left) isMouseLeftButtonDown = true;
            if(e.Button == MouseButtons.Right) isMouseRightButtonDown = true;
        };

        this.MouseUp += (s, e) => {
            if(isMouseLeftButtonDown && (e.Button == MouseButtons.Left)) isMouseLeftButtonDown = false;
            if(isMouseRightButtonDown && (e.Button == MouseButtons.Right)) isMouseRightButtonDown = false;
        };

        tbHue.MouseWheel += (s, e) => {
            if(isShiftDown) {
                zoom += (e.Delta > 0 ? 1 : -1) * 0.04;
                ReCalculateTransformations();
            }
        };

        tbHue.Scroll += (s, e) => {
            sr.ColorSchema = new ColorSchema(tbHue.Value);
            this.Invalidate();
        };
        
        this.MouseMove += (s, e) => {
            if(isMouseLeftButtonDown) {
                screenXY.X += e.Location.X - mouseLocation.X;
                screenXY.Y += e.Location.Y - mouseLocation.Y;
            }

            if(isMouseRightButtonDown) {
                double xDelta = e.Location.X - mouseLocation.X;
                double yDelta = e.Location.Y - mouseLocation.Y;

                observableXYZ.y -= xDelta;
                observableXYZ.z += yDelta;
            }

            mouseLocation = e.Location;

            if(isMouseLeftButtonDown || isMouseRightButtonDown) ReCalculateTransformations();
        };
    }

    private void ReCalculateTransformations() {
        sr.ReCalculateTransformationsCoeficients(observableXYZ.x, observableXYZ.y, observableXYZ.z, screenXY.X, screenXY.Y, ClientRectangle.Width, ClientRectangle.Height, zoom, 0, 0);
        this.Invalidate();
    }
}