Draw a single pixel on Windows Forms

Question

I'm stuck trying to turn on a single pixel on a Windows Form.

graphics.DrawLine(Pens.Black, 50, 50, 51, 50); // draws two pixels

graphics.DrawLine(Pens.Black, 50, 50, 50, 50); // draws no pixels

The API really should have a method to set the color of one pixel, but I don't see one.

I am using C#.

Answer 1

This will set a single pixel:

e.Graphics.FillRectangle(aBrush, x, y, 1, 1);

Answer 2

The Graphics object doesn't have this, since it's an abstraction and could be used to cover a vector graphics format. In that context, setting a single pixel wouldn't make sense. The Bitmap image format does have GetPixel() and SetPixel(), but not a graphics object built on one. For your scenario, your option really seems like the only one because there's no one-size-fits-all way to set a single pixel for a general graphics object (and you don't know EXACTLY what it is, as your control/form could be double-buffered, etc.)

Why do you need to set a single pixel?

Answer 3

Just to show complete code for Henk Holterman answer:

Brush aBrush = (Brush)Brushes.Black;
Graphics g = this.CreateGraphics();

g.FillRectangle(aBrush, x, y, 1, 1);

Answer 4

Where I'm drawing lots of single pixels (for various customised data displays), I tend to draw them to a bitmap and then blit that onto the screen.

The Bitmap GetPixel and SetPixel operations are not particularly fast because they do an awful lot of boundschecking, but it's quite easy to make a 'fast bitmap' class which has quick access to a bitmap.

Answer 5

Apparently DrawLine draws a line that is one pixel short of the actual specified length. There doesn't seem to be a DrawPoint/DrawPixel/whatnot, but instead you can use DrawRectangle with width and height set to 1 to draw a single pixel.

Answer 6

MSDN Page on GetHdc

I think this is what you are looking for. You will need to get the HDC and then use the GDI calls to use SetPixel. Note, that a COLORREF in GDI is a DWORD storing a BGR color. There is no alpha channel, and it is not RGB like the Color structure of GDI+.

This is a small section of code that I wrote to accomplish the same task:

public class GDI
{
    [System.Runtime.InteropServices.DllImport("gdi32.dll")]
    internal static extern bool SetPixel(IntPtr hdc, int X, int Y, uint crColor);
}

{
    ...
    private void OnPanel_Paint(object sender, PaintEventArgs e)
    {
        int renderWidth = GetRenderWidth();
        int renderHeight = GetRenderHeight();
        IntPtr hdc = e.Graphics.GetHdc();

        for (int y = 0; y < renderHeight; y++)
        {
            for (int x = 0; x < renderWidth; x++)
            {
                Color pixelColor = GetPixelColor(x, y);

                // NOTE: GDI colors are BGR, not ARGB.
                uint colorRef = (uint)((pixelColor.B << 16) | (pixelColor.G << 8) | (pixelColor.R));
                GDI.SetPixel(hdc, x, y, colorRef);
            }
        }

        e.Graphics.ReleaseHdc(hdc);
    }
    ...
}

Answer 7

Drawing a Line 2px using a Pen with DashStyle.DashStyle.Dot draws a single Pixel.

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        using (Pen p = new Pen(Brushes.Black))
        {
            p.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
            e.Graphics.DrawLine(p, 10, 10, 11, 10);
        }
    }