Dynamically drawing and displaying pixel by pixel with some delay

Question

Suppose I need to draw pixel by pixel with some delay so that the points are displayed one by one. I wrote the following code:

            for (int i = 0; i < 300; ++i)
        {
            Random random = new Random();
            Point point = new Point(random.Next(0, bmp.Width), random.Next(0, bmp.Height));
            bmp.SetPixel(point.X, point.Y, Color.Black);
            pictureBox1.Image = bmp;
            Thread.Sleep(10);
        }

But it doesn't work! The program freezes until 300 points are set on the bitmap, and then displays them all at the same time on the pictureBox

What am I doing wrong ? I didn't find anything about that.

I would be grateful for any advice, why this is happening and how to fix it. Sorry for my bad english.

Speed in obviously not of concern here. Lockbits has nothing to do with it. The UI updates only happen when there is time. The only thing missing was a Refresh to enforce the update.. — TaW, Dec 15 '18 at 14:16
As a matter of principle you should use only one and the same Random object, not always create new ones. — TaW, Dec 15 '18 at 14:18

score 0 · Accepted Answer · answered Dec 15 '18 at 13:47

I managed to make a working solution for you:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private Bitmap bmp = new Bitmap(100,100);

    private void Form1_Load(object sender, EventArgs e)
    {
        pictureBox1.Image = bmp; //only assign it once!
    }

    private async void button1_Click(object sender, EventArgs e)
    { // method that starts the picturebox filling. You can declare it anywhere else.
        for (int i = 0; i < 300; ++i)
        {
            Random random = new Random();
            Point point = new Point(random.Next(0, bmp.Width), random.Next(0, bmp.Height));
            bmp.SetPixel(point.X, point.Y, Color.Black); //we are updating the reference of 'bmp', which the pictureBox already contains
            pictureBox1.Refresh(); //force the picturebox to redraw its bitmap
            await Task.Delay(100); // async delay, to prevent the UI from locking
        }
    }
}

Because of `Thread.Sleep`. You should avoid using it if you're not working with separate `Threads`. Always use TPL `Task` for doing multithreading, if you can. Also check this out https://stackoverflow.com/questions/20082221/when-to-use-task-delay-when-to-use-thread-sleep — garry man, Dec 15 '18 at 14:13
PS> Other changes I've made to your code are for performance reasons. — garry man, Dec 15 '18 at 14:18

Dynamically drawing and displaying pixel by pixel with some delay

1 Answers1