MDI Background image problem

Jayakrishnan,

Did setting DoubleBuffered to true resolve the flickering problem?

Zoran

I think it will not help. You can try this code for instance:

using System.Drawing;
using System.Windows.Forms;

namespace ImageTest
{

    class Program
    {

        private class MyForm: Form
        {

            public MyForm()
            {

                _backgroundImage = new Bitmap(500, 500);

                using (Graphics gr = Graphics.FromImage(_backgroundImage))
                {
                    gr.FillRectangle(new SolidBrush(Color.Gray), new Rectangle(0, 0, 500, 500));
                    gr.FillEllipse(new SolidBrush(Color.DarkRed), new Rectangle(0, 0, 500, 500));
                }

                this.BackgroundImage = _backgroundImage;

            }

            protected override void OnFormClosed(FormClosedEventArgs e)
            {
                base.OnFormClosed(e);
                _backgroundImage.Dispose();
            }

            private Image _backgroundImage;

        }

        static void Main(string[] args)
        {
            MyForm f = new MyForm();
            f.ShowDialog();
        }

    }
}

Wait for it to open the form and then maximize the form. You'll see flickering. It comes from the form acting upon Window message to draw background - instead of drawing the image immediately, it first draws background in solid brush. This is probably done because .NET doesn't know whether the background image contains some transparent parts, etc. so Form tries to be sure that its background will be solidly filled even after the image is applied. Anyway, that kind of worry leads to flickering.

Now, modify MyForm and add this method:
protected override void OnPaintBackground(PaintEventArgs e)
{
    //base.OnPaintBackground(e);
    for (int x = 0; x < ClientSize.Width; x += _backgroundImage.Width)
        for (int y = 0; y < ClientSize.Height; y += _backgroundImage.Height)
            e.Graphics.DrawImage(_backgroundImage, new Point(x, y));
}

And repeat the test - open the form, then maximize it, resize it manually, etc. You'll see that flickering has gone. Off course, if you uncomment the base.OnPaintBackground call, flickering will be back again.

This example shows how to stop flickering in some cases, but in every particular case it is up to the programmer to know what should be done by the form.

Same effect in this case can be obtained by adding this to the constructor:

this.DoubleBuffered = true;

However, you don't have DoubleBuffered property available at all times. If you're coding custom control then your control will be instantiated by a form which might have DoubleBuffered set to false and you can't do anything about it.

Zoran

Welcome to the club...

First try setting form's DoubleBuffered property to true. It is a protected property which is by default set to false. So you have to set it to true in form's constructor.

Zoran

That is probably because form draws its background (in solid color) and only then draws the image. Flickering is an eternal problem in .NET.

Zoran