How can I stop flickering when I have a large number of dynamically created rectangles to display on screen.

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C#

graphics

Bitmap

2D

I have a large number of dynamically created rectangles to display on screen. Through trial and error I now draw only the rectangles that have changed to a bitmap and the bitmap in a OnPaint event, but i still get flickering. Any suggestions on where I might be going wrong.

I'm using VS 2015 .Net 4.5. I create a new Windows Forms project. Set with height and width of the form to 550 and add one button and name it bRunTask. I create an instance of PathAViewModel (class lib based on path find A star) 50 columns x 50 rows. Then subscribe to the OnUpdate event. OnUpdate passes an int that corresponds to any rectangle that state has changed. I get the state and redraw the rectangle with its new color and Invalidate about 30 times a sec. Then make a call to PathAViewmodel.RunTask in the button click event.

I'v included the relevant code below will attached two project files. One for this project and one for the class Lib.if requested.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using PathAStarlib;
using System.Diagnostics;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;

namespace wfBitmapDisplay
{
    public partial class Form1 : Form
    {
        PathAViewModel MyView;
        

        Rectangle[] MyRecArry;
        Stopwatch MyWatch = new Stopwatch();

        Graphics gDisplay;
        Bitmap bitmap;
        Graphics gBitmap;
        Brush MyBrush;

        public Form1()
        {
            InitializeComponent();

            bitmap = new Bitmap(this.Width, this.Height, PixelFormat.Format32bppArgb);
            gBitmap = Graphics.FromImage(bitmap);
            gBitmap.CompositingMode = CompositingMode.SourceCopy;

            MyView = new PathAViewModel(50,50);
            MyView.OnUpdate += new PathAViewModel.UpdateDisplayHandler(RunOnUpdate);

            this.Paint += Form1_Paint;
            this.DoubleBuffered = true;
            SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

            InitMyComponents();

            gDisplay = this.CreateGraphics();

            gBitmap.DrawRectangles(Pens.Black, MyRecArry);
        }
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            gDisplay.DrawImage(bitmap, new Point(0, 0));
        }
        private void bRunTask_Click(object sender, EventArgs e)
        {
            MyView.RunTask();
        }
        private void RunOnUpdate(int x)
        {
            
            foreach (Node n in MyView.MyModel.lNodes.Where(u => u.Id == x))
            {
                switch (n.ToString())
                {
                    case "1":
                        MyBrush = Brushes.Aqua;
                        break;
                    case "2":
                        MyBrush = Brushes.Blue;
                        break;
                    case "3":
                        MyBrush = Brushes.Red;
                        break;
                    case "4":
                        MyBrush = Brushes.Green;
                        break;
                    case "5":
                        MyBrush = Brushes.Black;
                        break;
                    case "6":
                        MyBrush = Brushes.Yellow;
                        break;
                    default:
                        MyBrush = Brushes.White;
                        break;

                }
                gBitmap.FillRectangle(MyBrush, MyRecArry[n.Id - 1]);
            }
            if (MyWatch.ElapsedMilliseconds % 35 == 0)
                Invalidate();
        }
        
        private void InitMyComponents()
        {
            bRunTask.Top = this.Bottom - 60;
            bRunTask.Text = "Find Path";

            MyRecArry = new Rectangle[MyView.Columns * MyView.Rows];
            int x = 0;
            for (int r = 1; r <= MyView.Rows; r++)
            {
                for (int c = 1; c <= MyView.Columns; c++)
                {
                    MyRecArry[x].Width = ((bitmap.Width - 10) / MyView.Columns);
                    MyRecArry[x].Height = ((bitmap.Height - 50) / MyView.Rows);
                    MyRecArry[x].X = (c - 1) * MyRecArry[x].Width;
                    MyRecArry[x].Y = (r - 1) * MyRecArry[x].Height;
                    x++;
                }

            }

            foreach (Node n in MyView.MyModel.lNodes.Where(u => u.Id == MyView.MyModel.StartId))
                gBitmap.FillRectangle(Brushes.Green, MyRecArry[n.Id - 1]);
            foreach (Node n in MyView.MyModel.lNodes.Where(u => u.Id == MyView.MyModel.FinishId))
                gBitmap.FillRectangle(Brushes.Red, MyRecArry[n.Id - 1]);
            foreach (Node n in MyView.MyModel.lNodes.Where(u => u.IsPassable == false))
                gBitmap.FillRectangle(Brushes.Black, MyRecArry[n.Id - 1]);
        }

       
    }
}