Transparent Overlapping Circular Progress Bars (Custom Control)

Question

I am having some trouble with a custom circular progress bar control. I am trying to overlap the two of them at the lower right corner. It has a transparent background, whic

Answer 1

I'm going to give you just a couple of suggestions on how to proceed.

Start off with this bare-bones transparent control (TransparentPanel).
This class is derived from Panel. That's the first choice to make: is Panel the right control to inherit from/extend for this task? Maybe it is, maybe not.
For example, a Panel is a container. Do you need the features of a container, here? Container means a lot. It inherits ScrollableControl and has ContainerControl among its Window styles. It comes with a baggage already.

You could opt for a Label instead, it's light-weight. Or build a UserControl.
I don't think there's an absolute best choice. It depends of what this custom control is used for. You need to try it out.

class TransparentPanel : Panel
{
    internal const int WS_EX_TRANSPARENT = 0x00000020;

    public TransparentPanel() => InitializeComponent();

    protected void InitializeComponent()
    {
        this.SetStyle(ControlStyles.AllPaintingInWmPaint |
                      ControlStyles.Opaque |
                      ControlStyles.ResizeRedraw |
                      ControlStyles.SupportsTransparentBackColor |
                      ControlStyles.UserPaint, true);
        this.SetStyle(ControlStyles.OptimizedDoubleBuffer, false);
    }

    protected override CreateParams CreateParams
    {
        get {
            CreateParams parameters = base.CreateParams;
            parameters.ExStyle |= WS_EX_TRANSPARENT;
            return parameters;
        }
    }
}

---

Notes:
Here, ControlStyles.SupportsTransparentBackColor is set explicitly. The Panel class already supports this. It's specified anyway because it gives the idea of what this custom control is for just reading at its constructor.

Also, ControlStyles.OptimizedDoubleBuffer is set to false.
This prevents the System to interfere in any way with the painting of the control. There's not caching, the Custom Control is painted new when it's Invalidated. The container Form should preferably have its DoubleBuffer property set to true, but you might want test it without, to see if there's a difference.

---

This Custom Control (not to be confused with a UserControl) is completely transparent. It doesn't draw its background. But you can paint anything on its surface.

Take the links posted before:

• This Translucent Label (no BackGround painting, disabled DoubleDuffering)
• Reza Aghaei's transparent Panel (using Opacity in a different way)
• TaW's Grid Panel (Color.Transparent and DoubleBuffer)
• These notes: Reasons for why a WinForms label does not want to be transparent?

4 different ways to get to the same result. Which one to choose depends on the context/destination.

A design-time advice: when you are testing a custom control functionalities, remember to always rebuild the project. It can happen that a CustomControl, droppen on a Form from the Toolbox, is not updated with the new changes when the project is run.
Also, if you add or remove properties, you need to delete the control, rebuild and drop a new one on the Form.
If you don't, there's a really good chance that your modification/addition are completely ignored and you keep on testing features that never get into play.

An example, using 2 overlapping custom controls.
(using the bare-bones custom TransparentPanel)

This is the test code used to generate these drawings:

• Create a new Custom Control using the TransparentPanel class shown before:
• Drop two TransparentPanel objects on a test Form
• Assign to TransparentPanel1 and TransparentPanel2 the transparentPanel1_Paint and transparentPanel2_Paint event handlers.
• Overlap the two transparent Panels, making sure you don't nest them by mistake.
• Adapt the rest of the code (you need just a Button, here named btnRotate, assign the btnRotate_Click handler)

private System.Windows.Forms.Timer RotateTimer = null;
private float RotationAngle1 = 90F;
private float RotationAngle2 = 0F;
public bool RotateFigures = false;

public form1()
{
    InitializeComponent();
    RotateTimer = new Timer();
    RotateTimer.Interval = 50;
    RotateTimer.Enabled = false;
    RotateTimer.Tick += new EventHandler(this.RotateTick);
}

protected void RotateTick(object sender, EventArgs e)
{
    RotationAngle1 += 10F;
    RotationAngle2 += 10F;
    transparentPanel1.Invalidate();
    transparentPanel2.Invalidate();
}

private void btnRotate_Click(object sender, EventArgs e)
{
    RotateTimer.Enabled = !RotateTimer.Enabled;
    if (RotateTimer.Enabled == false)
    {
        RotateFigures = false;
        RotationAngle1 = 90F;
        RotationAngle2 = 0F;
    }
    else
    {
        RotateFigures = true;
    }
}


private void transparentPanel1_Paint(object sender, PaintEventArgs e)
{
    if (!RotateFigures) return;
    e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
    e.Graphics.CompositingQuality = CompositingQuality.HighQuality;
    e.Graphics.CompositingMode = CompositingMode.SourceOver;
    Rectangle rect = transparentPanel1.ClientRectangle;
    Rectangle rectInner = rect;

    using (Pen transpPen = new Pen(transparentPanel1.Parent.BackColor, 10))
    using (Pen penOuter = new Pen(Color.SteelBlue, 8))
    using (Pen penInner = new Pen(Color.Teal, 8))
    using (Matrix m1 = new Matrix())
    using (Matrix m2 = new Matrix())
    {
        m1.RotateAt(-RotationAngle1, new PointF(rect.Width / 2, rect.Height / 2));
        m2.RotateAt(RotationAngle1, new PointF(rect.Width / 2, rect.Height / 2));
        rect.Inflate(-(int)penOuter.Width, -(int)penOuter.Width);
        rectInner.Inflate(-(int)penOuter.Width * 3, -(int)penOuter.Width * 3);

        e.Graphics.Transform = m1;
        e.Graphics.DrawArc(transpPen, rect, -4, 94);
        e.Graphics.DrawArc(penOuter, rect, -90, 90);
        e.Graphics.ResetTransform();
        e.Graphics.Transform = m2;
        e.Graphics.DrawArc(transpPen, rectInner, 190, 100);
        e.Graphics.DrawArc(penInner, rectInner, 180, 90);
    }
}

private void transparentPanel2_Paint(object sender, PaintEventArgs e)
{
    if (!RotateFigures) return;
    e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
    e.Graphics.CompositingQuality = CompositingQuality.HighQuality;
    e.Graphics.CompositingMode = CompositingMode.SourceOver;
    Rectangle rect = transparentPanel2.ClientRectangle;
    Rectangle rectInner = rect;

    using (Pen transpPen = new Pen(transparentPanel2.Parent.BackColor, 10))
    using (Pen penOuter = new Pen(Color.Orange, 8))
    using (Pen penInner = new Pen(Color.DarkRed, 8))
    using (Matrix m1 = new Matrix())
    using (Matrix m2 = new Matrix())
    {
        m1.RotateAt(RotationAngle2, new PointF(rect.Width / 2, rect.Height / 2));
        m2.RotateAt(-RotationAngle2, new PointF(rect.Width / 2, rect.Height / 2));
        rect.Inflate(-(int)penOuter.Width, -(int)penOuter.Width);
        rectInner.Inflate(-(int)penOuter.Width * 3, -(int)penOuter.Width * 3);

        e.Graphics.Transform = m1;
        e.Graphics.DrawArc(transpPen, rect, -4, 94);
        e.Graphics.DrawArc(penOuter, rect, 0, 90);
        e.Graphics.ResetTransform();
        e.Graphics.Transform = m2;
        e.Graphics.DrawArc(transpPen, rectInner, 190, 100);
        e.Graphics.DrawArc(penInner, rectInner, 180, 90);
    }
}

Note: To create the rotation effect with this code, you need the TransparentPanel Control shown above, it won't work the same way drawing on the surface of a standard Control.