How Can I Efficiently Draw on a PictureBox Using a Separate Method in C#?

C# PictureBox drawing: efficient techniques using independent methods

In C# forms applications, you can draw custom graphics on the PictureBox control. However, users may encounter problems when trying to do this via a separate method.

Question:

A user may wish to create a method to easily draw a circle on a PictureBox, but find that this method does not produce the expected results. The problem method initializes the bitmap, graphics object, and brush used to draw the circle. However, when called within the PictureBox's Paint event handler, it fails to draw the circle correctly.

Solution:

To effectively use separate methods to draw on a PictureBox, it is important to make it clear whether the goal is to draw within the image displayed by the PictureBox, or directly within the control itself.

Method 1: Draw directly on the control

To draw directly on the control (without affecting the image), use the PictureBox's Paint event handler as follows:

private void pictureBox2_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.DrawEllipse(Pens.Red, new Rectangle(3, 4, 44, 44));
}

In this case, the drawing is persistent and the graphic is bound to the control, following any resizing or movement of the control.

Method 2: Drawing in the image

To draw on the image displayed by the PictureBox, create a separate method and draw using the Graphics object obtained from the PictureBox's Image property.

void drawIntoImage()
{
    using (Graphics G = Graphics.FromImage(pictureBox1.Image))
    {
        G.DrawEllipse(Pens.Orange, new Rectangle(13, 14, 44, 44));
    }
    pictureBox1.Refresh();
}

After drawing is completed, call the PictureBox's Refresh() method to update the display. In this case, the shape is persistent to the image and will be affected by any scaling or transformation of the image.

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