How can I get a screenshot of control? DrawToBitmap not working

问题

I have a pictureBox that's being painted to externally via a dll call.

private void myPictureBox_Paint(object sender, PaintEventArgs e)
{
     dllClass.RefreshEx(LWHANDLE, 0, 0);
}

This is working and all, but I now need to get a screenshot of that picturebox, and it's not working.

Here's what I've tried:

        Control ctrlToDraw = myPictureBox;

        System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(ctrlToDraw.Width, ctrlToDraw.Height);
        ctrlToDraw.DrawToBitmap(bmp, ctrlToDraw.ClientRectangle);

I've also attempted to do it via Windows API, but it's resulting in exactly the same result as the above code: a blank (not null) image.

Could anyone name some suggestions apart from taking a screenshot of the whole screen?

回答1:

I don't know how much control you have over the external program, or how it draws to your picture box, but if you are using createGraphics it wont work.

private void button1_Click(object sender, EventArgs e)
    {
        //here I am calling the graphics object of the Picture Box, this will draw to the picture box
        //But the DrawToBitmap, will not reflect this change, and once the Picturebox needs to be updated, this will disappear.
        Graphics g = pictureBox1.CreateGraphics();
        g.DrawRectangle(Pens.Blue, 10, 10, 20, 20);

        System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(pictureBox1.Width, pictureBox1.Height);
        Rectangle bounds = new Rectangle(Left, Top, Width, Height);
        pictureBox1.DrawToBitmap(bmp, pictureBox1.ClientRectangle);
        //Draws whatever is in the PictureBox to the Forms BackgroundImage
        this.BackgroundImage = bmp;
        //It will not draw the Blue rectangle

    }

If your external program was to draw to a bitmap, then you could set that bitmap to the picturebox background

    Bitmap buffer;
    public Form1()
    {
        InitializeComponent();
        buffer = new Bitmap(pictureBox1.Width, pictureBox1.Height);
    }


    private void button1_Click(object sender, EventArgs e)
    {
        //draw to the bitmap named buffer
        using (Graphics g = Graphics.FromImage(buffer))
        {
            g.DrawRectangle(Pens.Blue, 10, 10, 20, 20);
        }
        //assign the picturebox image to buffer
        pictureBox1.Image = buffer;

        //Now this will show the blue rectangle
        System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(pictureBox1.Width, pictureBox1.Height);
        Rectangle bounds = new Rectangle(Left, Top, Width, Height);
        pictureBox1.DrawToBitmap(bmp, pictureBox1.ClientRectangle);

        this.BackgroundImage = bmp;
    }

EDIT Third Times the Charm right

This will take a screen shot, cut the picturebox out, and then I changed the Forms Background, just to prove it worked.

You will need to add

using System.Drawing.Imaging;

it is for the Pixel format.

 private void button1_Click(object sender, EventArgs e)
    {
        using (Graphics G = pictureBox1.CreateGraphics())
        {
            G.DrawRectangle(Pens.Blue, 10, 10, 10, 10);
        }
        Bitmap BMP = new Bitmap(Screen.PrimaryScreen.Bounds.Width,
                                        Screen.PrimaryScreen.Bounds.Height,
                                        PixelFormat.Format32bppArgb);
        using (Graphics GFX = Graphics.FromImage(BMP))
        {
            GFX.CopyFromScreen(Screen.PrimaryScreen.Bounds.X,
                                Screen.PrimaryScreen.Bounds.Y,
                                0, 0,
                                Screen.PrimaryScreen.Bounds.Size,
                                CopyPixelOperation.SourceCopy);
        }
        Bitmap YourPictureBoxImage = new Bitmap(pictureBox1.Width,pictureBox1.Height);
        using (Graphics g = Graphics.FromImage(YourPictureBoxImage))
        {
            Point np = pictureBox1.PointToScreen(new Point(0, 0));
            g.DrawImage(BMP,new Rectangle(0,0,100,100),new Rectangle(np,pictureBox1.Size),GraphicsUnit.Pixel);
        }

        this.BackgroundImage = YourPictureBoxImage;
    }

回答2:

You can take a screenshot of just the active window by using ALT+PRINTSCREEN. That will capture the current active window as a bitmap to the clipboard. Paste that into a bitmap editing tool, crop to just the area you want.

Or use a screen capture utility that allows for cropping of the target area while on screen such as Evernote version 2's old screen clipper.

来源：https://stackoverflow.com/questions/10741384/how-can-i-get-a-screenshot-of-control-drawtobitmap-not-working

标签

.net

winforms

drawtobitmap