Draw a Fill Rectangle with low opacity

问题

I a have a PictureBox with a picture in a Windows Form application in C# language.I want draw a FillRectangle in some location of picturebox.but i also need to see picture of picture box.how can i draw this rectangle with low opacity to see image of picturebox?

回答1:

Do you mean:

using (Graphics g = Graphics.FromImage(pb.Image))
{
    using(Brush brush = new SolidBrush(your_color))
    {
        g.FillRectangle(brush , x, y, width, height);
    }
}

or you can use

Brush brush = new SolidBrush(Color.FromArgb(alpha, red, green, blue))

where alpha goes from 0 to 255, so a value of 128 for your alpha will give you 50% opactity.

回答2:

You need to create a Graphics object based on your PictureBox image and draw what you want on it:

Graphics g = Graphics.FromImage(pictureBox1.Image);
g.FillRectangle(Brushes.Red, new Rectangle(10, 10, 200, 200))
pictureBox1.Refresh()

Or as suggested by @Davide Parias you can use Paint event handler:

private void pictureBox_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.FillRectangle(Brushes.Red, new Rectangle(10, 10, 200, 200));
}

来源：https://stackoverflow.com/questions/7580145/draw-a-fill-rectangle-with-low-opacity