Transparent controls on painted form

Question

Using C# WinForms I've got a form that I'm painting a gradient background on it from say light blue to dark blue. I've got some buttons and a couple of labels on it which I've already tried setting the backcolor to transparent as I want the background to show through - especially for the labels, but that doesn't seem to work.

But I've noticed that the painting is also paining the labels, even though the code is only on the form_paint event.

How can I make the labels not contain the same grade shading, but to be transparent? e.g. the labels at the top of the form will be light blue, but the ones at the bottom will be dark blue.

private void frmOptions_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
    Rectangle rectangle = e.ClipRectangle;

    using (Brush aBrush = new LinearGradientBrush(rectangle, Color.LightBlue, Color.DarkBlue, LinearGradientMode.Vertical))
    {
        e.Graphics.FillRectangle(aBrush, rectangle);
    }
}

Many thanks for any help on this.

EDIT: I've just been stepping through the lines of code to debug it and noticed that the paint event is being called for EACH object on the form - the labels & buttons, the rectangle on line 2 above has the size of each time. So I'm now really confused why it's getting called for each object on the form.

EDIT 2: Just been stepping through the code of my quick test project (see comment below) and also noticed that the paint event is beening called for each object. the differenece is that the test project doesn't have the line "Rectangle rectangle = e.ClipRectangle;" - it basically uses the width & height of the form. where my code above sets rectangle to ClipRectangle - which is the size of each label & button... Is this Normal behaviour ? If so, then it looks like I need to folow the answer below by Reniuz.

EDIT 3 I've change the cliprectangle line to "Rectangle rectangle = new Rectangle(0, 0, this.Width, this.Height);" This seems to make the transparent look how it should, but the paint event is still being called for every object on the form - good job there is only 7 of the, so it's drawing 8 times :( Think I'll still look at the "TransparentLabel" code to test that.

Answer 1

Take a look at this article.

Edit:

Also you can use this code:

public class TransparentLabel : Control
{
    public TransparentLabel(Label label)
    {
        //setting default properties
        this.Text = label.Text;
        this.Font = label.Font;
        this.Location = label.Location;
        this.Size = label.Size;
        this.Parent = label.Parent;
        this.BringToFront();
        label.Dispose();

        TabStop = false;
    }

    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.ExStyle |= 0x20;
            return cp;
        }
    }

    protected override void OnPaintBackground(PaintEventArgs e)
    {
        // do nothing
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        DrawText();
    }

    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        if(m.Msg == 0x000F)
        {
            DrawText();
        }
    }

    private void DrawText()
    {
        using(Graphics graphics = CreateGraphics())
        using(SolidBrush brush = new SolidBrush(ForeColor))
        {
            SizeF size = graphics.MeasureString(Text, Font);

            // first figure out the top
            float top = 0;
            switch(textAlign)
            {
                case ContentAlignment.MiddleLeft:
                case ContentAlignment.MiddleCenter:
                case ContentAlignment.MiddleRight:
                    top = (Height - size.Height) / 2;
                    break;
                case ContentAlignment.BottomLeft:
                case ContentAlignment.BottomCenter:
                case ContentAlignment.BottomRight:
                    top = Height - size.Height;
                    break;
            }

            float left = -1;
            switch(textAlign)
            {
                case ContentAlignment.TopLeft:
                case ContentAlignment.MiddleLeft:
                case ContentAlignment.BottomLeft:
                    if(RightToLeft == RightToLeft.Yes)
                        left = Width - size.Width;
                    else
                        left = -1;
                    break;
                case ContentAlignment.TopCenter:
                case ContentAlignment.MiddleCenter:
                case ContentAlignment.BottomCenter:
                    left = (Width - size.Width) / 2;
                    break;
                case ContentAlignment.TopRight:
                case ContentAlignment.MiddleRight:
                case ContentAlignment.BottomRight:
                    if(RightToLeft == RightToLeft.Yes)
                        left = -1;
                    else
                        left = Width - size.Width;
                    break;
            }
            graphics.DrawString(Text, Font, brush, left, top);
        }
    }

    public override string Text
    {
        get
        {
            return base.Text;
        }
        set
        {
            base.Text = value;
            RecreateHandle();
        }
    }

    public override RightToLeft RightToLeft
    {
        get
        {
            return base.RightToLeft;
        }
        set
        {
            base.RightToLeft = value;
            RecreateHandle();
        }
    }

    public override Font Font
    {
        get
        {
            return base.Font;
        }
        set
        {
            base.Font = value;
            RecreateHandle();
        }
    }

    private ContentAlignment textAlign = ContentAlignment.TopLeft;
    public ContentAlignment TextAlign
    {
        get { return textAlign; }
        set
        {
            textAlign = value;
            RecreateHandle();
        }
    }
}

Transparent label will replace your existing label so you can use it like this:

TransparentLabel transparentLabel1 = new TransparentLabel(label1);
TransparentLabel transparentLabel2 = new TransparentLabel(label2);

and then you should see the result(design time on left, run time on right):