C＃同时绘制多个圆圈

Question

I tried to build my own Polar Chart . I use a function to draw points as follows:

private void drawPoints()
{
    this.SuspendLayout();
    Graphics g = this.CreateGraphics();

    int i = 0;
    foreach (Point Pointaktuell in PointList)
    {
        int radius = 15;

        Brush b = new SolidBrush(Color.Red);

        g.FillEllipse(b, (int)(Pointaktuell.X - radius / 2.0), (int)(Pointaktuell.Y - radius / 2.0), radius, radius);
        i++;
    }
    PointList.Clear();
    this.ResumeLayout();
}

The problem is that the points are draw one after one, and need a lot of time. How can I draw them all at once?

Answer 1

To optimize the drawing procedure, try put as more code as you can outside the loop. Do not forget to close IDisposable

private void drawPoints() 
{
    SuspendLayout();

    try 
    {
        using (Graphics g = CreateGraphics()) 
        {
            int i = 0; 
            int radius = 15;

            using (b = new SolidBrush(Color.Red)) 
            {
                foreach (Point Pointaktuell in PointList) 
                {
                    g.FillEllipse(b, (int)(Pointaktuell.X - radius / 2.0), (int)(Pointaktuell.Y - radius / 2.0), radius, radius);
                    i += 1;
                }
            }
        }
   }
   finally { ResumeLayout(); }
}

Answer 2

A new SolidBrush instantiated in each loop step. And radius is redefined every time again and again. Dispose() routine is not called for Instantiated objects (which comes to be important for Graphics )

You might try the following;

private void drawPoints()
{
    this.SuspendLayout();

    const int radius = 15;
    using (Graphics g = this.CreateGraphics())
    {
        //if (g == null) { this.ResumeLayout(); return; } // # Uncomment this line if you want defensive checks
        using (Brush b = new SolidBrush(Color.Red))
        {
            for (int i = 0; i < PointList.Count; i++)
            {
                g.FillEllipse(b, (int)(PointList[i].X - radius / 2.0), (int)(PointList[i].Y - radius / 2.0), radius, radius);
            }
        }
    }

    PointList.Clear();
    this.ResumeLayout();
}

This is only if you'r going to do all drawing stuff in drawPoints() and call it once in a time. If you'r going to call drawPoints() periodically or have more drawing routines in other parts of the flow; i suggest you keep that Graphics g and Brush b referances globally and Dispose() when they are no longer needed (no more drawing in this case)