C# Efficent way to get color at point on screen

Question

I do have a working method however it is fairly resource intensive and I am looking for a better way. Running the code below was suggested on a response to a similar question here.

However running said code yields a System.OutOfMemoryException.

The exception happens @ using (Graphics gdest = Graphics.FromImage(screenPixel)) {

Current code:

Bitmap screenPixel = new Bitmap(1, 1, PixelFormat.Format16bppArgb1555);
using (Graphics gdest = Graphics.FromImage(screenPixel)) {
    using (Graphics gsrc = Graphics.FromHwnd(IntPtr.Zero)) {
        IntPtr hSrcDC = gsrc.GetHdc();
        IntPtr hDC = gdest.GetHdc();
        int retval = BitBlt(hDC, 0, 0, 1, 1, hSrcDC, x, y, (int)CopyPixelOperation.SourceCopy);
        gdest.ReleaseHdc();
        gsrc.ReleaseHdc();
        }
   }
    return screenPixel.GetPixel(0, 0);

EDIT:

Okay so I've fixed the issue I was having above with the following code. However now I am only getting the color black (0,0,0) returned.

this.screenPixel = new Bitmap(1, 1, PixelFormat.Format16bppRgb555);
using (Graphics gdest = Graphics.FromImage(this.screenPixel)) {
    using (Graphics gsrc = Graphics.FromHwnd(IntPtr.Zero)) {
        IntPtr hSrcDC = gsrc.GetHdc();
        IntPtr hDC = gdest.GetHdc();
        int retval = BitBlt(hDC, 0, 0, width, height, hSrcDC, x, y, (int)CopyPixelOperation.SourceCopy);
        gdest.ReleaseHdc();
        gsrc.ReleaseHdc();
        }
}
Color result = screenPixel.GetPixel(0, 0);
Console.WriteLine(result.R + " " + result.G + " " + result.B);
GC.SuppressFinalize(this.screenPixel);
this.screenPixel.Dispose();
return result;

Why do you use `Format16bppArgb1555`? which line throws the exception? — TaW, Aug 12 '14 at 18:07
I have tried with and without, I only have it because I only need 8 bit color precision. I'll update the post as to which line throws the exception. — walshie4, Aug 12 '14 at 18:11
Is `screenPixel` a class member or a local variable? In the linked solution it is a class member that is reused (and hopefully disposed of in the Dispose method of the form). — dbc, Aug 12 '14 at 18:11
BTW: `using` already calls `Dispose`, why do you explicitly call it. Try by removing them.... — L.B, Aug 12 '14 at 18:11
I would use the format your screen is displaying or default. - which line throws the exception??? — TaW, Aug 12 '14 at 18:15
Does it throw an exception when you use PixelFormat.Format32bppArgb? — dbc, Aug 12 '14 at 18:15
You have to acutally dispose these objects, they take handles on system resources. — asawyer, Aug 12 '14 at 18:24
Just look for EyeDropper Examples in .NET and alter it to fit your needs: http://bobpowell.net/eyedropper.aspx — LiquaFoo, Aug 12 '14 at 18:41
@walshie4 The GDI+ objects hold references to windows resources that must be disposed. — asawyer, Aug 12 '14 at 19:09
@asawyer I'm releasing them. Which variable in particular are you referring to? — walshie4, Aug 12 '14 at 19:14

score 1 · Answer 1 · edited May 23 '17 at 12:20

This seems to work here:

using System.Runtime.InteropServices;
//... 


[DllImport("gdi32.dll")]
public static extern int BitBlt(IntPtr hObject, int nXDest, int nYDest, 
   int nWidth, int nHeight, IntPtr hObjSource, int nXSrc, int nYSrc, int  dwRop);

//..

    Bitmap screenPixel = new Bitmap(1, 1, PixelFormat.Format32bppRgb);
    using (Graphics gdest = Graphics.FromImage(screenPixel))
    {
        using (Graphics gsrc = Graphics.FromHwnd(IntPtr.Zero))
        {
            IntPtr hSrcDC = gsrc.GetHdc();
            IntPtr hDC = gdest.GetHdc();
            int retval = BitBlt(hDC, 0, 0, 1, 1, hSrcDC, x, y,
                                    (int) CopyPixelOperation.SourceCopy);
            gdest.ReleaseHdc();
            gsrc.ReleaseHdc();
        }
    }
    Color c =  screenPixel.GetPixel(0, 0);
    return c;

Note 1:

I have changed the pixel format to match my screen.
I have fiddled with the BitBlt declaration

Note 2:

According to this post you might as well use Graphics.CopyFromScreen directly as it will use BitBlt anyway. This would be safer and less trouble imo.

Can you tell me where the `(int)0x00CC0020` value comes from? — walshie4, Aug 12 '14 at 18:45
[Here on pinvoke](http://www.pinvoke.net/default.aspx/gdi32.bitblt) is a description of bitBlt and the `enum TernaryRasterOperations`. Since I thought it was missing I copied the value for `SRCCOPY`. Silly me! Note that you may want to use `int bpp = Screen.PrimaryScreen.BitsPerPixel;` to determine the color depth of your screen. — TaW, Aug 12 '14 at 18:49

C# Efficent way to get color at point on screen

1 Answers1