My form is not printing correctly when DPI is 150%

Question

I have a form that prints correctly on my machine but when I deploy the application on another machine, the form does not fit on the page and the desktop background appears on the printed document. The primary differences between the two machines is that one has the DPI setting at 150%. I have changed auto scaling many times but nothing changes. The form looks ok on screen but just does not print correctly. Below is the code I am using.

private void btnPrint_Click(object sender, EventArgs e)
    {
        CaptureScreen();
        printPreviewDialog1.Document = printDocument1;
        printPreviewDialog1.ShowDialog();            
    }

    Bitmap memoryImage;

    private void CaptureScreen()
    {
        Graphics myGraphics = this.CreateGraphics();
        Size s = this.Size;
        memoryImage = new Bitmap(s.Width, s.Height, myGraphics);
        Graphics memoryGraphics = Graphics.FromImage(memoryImage);
        memoryGraphics.CopyFromScreen(this.Location.X, this.Location.Y, 0, 0, s);
    }

    private void printDocument1_PrintPage(System.Object sender,
           System.Drawing.Printing.PrintPageEventArgs e)
    {            
        e.Graphics.DrawImage(memoryImage, 0, 0);
    }

Why are you trying to print a web form? And are you sure the difference is not in the printing settings between the two machines? — Kevin, Mar 29 '16 at 20:53
The user needs to fill out, save, and print the Windows form. The form prints correctly when the DPI is at 100% or 125% but not at 150%. I have one user with vision problems so he runs the highest DPI setting. — wsb, Mar 29 '16 at 20:57
I will try to get one. The best way to describe it is if you started at the top left corner, then moved right and down about 50% of the form's size, zoomed in and then cropped the form, that's what you get. — wsb, Mar 29 '16 at 21:35

score 4 · Accepted Answer · edited May 23 '17 at 10:28

The higher dpi scaling is not (like the old 125% scaling) made by increasing the Windows font size and having the application handle the scaling, but by having the operating system do the scaling for you. In this mode, the operating system lies to the application about the actual dpi settings and does by itself scale the application when drawing its surface.

The result is that inside your application, the pixel positions and sizes are not the real ones used on the screen. But the CopyFromScreen() method requires the actual pixel coordinates and sizes. You need to find out the pixel scaling your application undergoes and then apply this scaling to the coordinates you use.

Here is the working code (The getScalingFactor() method was stolen from this answer).

[DllImport("gdi32.dll")]
static extern int GetDeviceCaps(IntPtr hdc, int nIndex);
public enum DeviceCap
{
    VERTRES = 10,
    DESKTOPVERTRES = 117,
}

private float getScalingFactor()
{
    using (Graphics g = Graphics.FromHwnd(IntPtr.Zero))
    {
        IntPtr desktop = g.GetHdc();
        try
        {
            int LogicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.VERTRES);
            int PhysicalScreenHeight = GetDeviceCaps(desktop, (int)DeviceCap.DESKTOPVERTRES);
            float ScreenScalingFactor = (float)PhysicalScreenHeight / (float)LogicalScreenHeight;
            return ScreenScalingFactor; 
        }
        finally
        {
            g.ReleaseHdc();
        }
    }
}

private void button1_Click(object sender, EventArgs e)
{
    using (Graphics myGraphics = this.CreateGraphics())
    {
        var factor = getScalingFactor();
        Size s = new Size((int)(this.Size.Width * factor), (int)(this.Size.Height * factor));

        using (Bitmap memoryImage = new Bitmap(s.Width, s.Height, myGraphics))
        {
            using (Graphics memoryGraphics = Graphics.FromImage(memoryImage))
            {
                memoryGraphics.CopyFromScreen((int)(Location.X * factor), (int)(Location.Y * factor), 0, 0, s);
                memoryImage.Save(@"D:\x.png", ImageFormat.Png);
            }
        }
    }
}

My form is not printing correctly when DPI is 150%

1 Answers1