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OpenGL Get Context

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Hey. I have injected dll to 3rd party opengl app. And now i need to get context of the app window.How can i get the context ?? Main goal is to take the screenshot. Im trying to take like fraps does in C#. This code i used to get but some how the screenshot is black. This is the only opengl function in dll. Bitmap b = new Bitmap(s.Width, s.Height, PixelFormat.Format32bppRgb); BitmapData bd = b.LockBits(new Rectangle(0, 0, s.Width, s.Height), ImageLockMode.WriteOnly, PixelFormat.Format32bppRgb); GL.glReadBuffer(GL.GL_BACK); GL.glReadPixels(0, 0, s.Width,s.Height, GL.GL_RGB, GL.GL_UNSIGNED_BYTE,bd.Scan0); //b.RotateFlip(); b.Save(@"D:\screen67023.Jpeg", ImageFormat.Jpeg); b.UnlockBits(bd); What Am i missing? Any help is good. Regards, KJ.

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Hi,
I'm not an expert of C# and how it is interfaced with OpenGL, so I cannot help you with the context... but seeing your code I've noticed that you are trying to read pixels from the Back Buffer:

GL.glReadBuffer(GL.GL_BACK);

Try read the front Buffer instead. Back buffer is often cleared immediately after the swap or immediately before begin a new frame so you cannot rely on its content.


I hope this can help

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Quote:
Original post by LordOrion
Hi,
I'm not an expert of C# and how it is interfaced with OpenGL, so I cannot help you with the context... but seeing your code I've noticed that you are trying to read pixels from the Back Buffer:

GL.glReadBuffer(GL.GL_BACK);

Try read the front Buffer instead. Back buffer is often cleared immediately after the swap or immediately before begin a new frame so you cannot rely on its content.


I hope this can help


Thanks for your help but GL_FRONT Same Black Screen.
But im buidling it in C# but C++ ways help allsow.

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Here is a bit of code I use to capture screen shots using C#

public static bool SaveGLBackbufferToBMP (string fullFilename)
{
string file = System.IO.Path.GetFileNameWithoutExtension(fullFilename);
byte [] buffer;
int size = 0;
int [] video = new int[4];
int video_width;
int video_height;
// --------------------------------------------------------------------
// Query for current Video Size
// --------------------------------------------------------------------
Gl.glGetIntegerv (Gl.GL_VIEWPORT,video);

// --------------------------------------------------------------------
// Allocate storage room
// --------------------------------------------------------------------
video_width = video[2];
video_height = video[3];
size = 3 * video_width * video_height;
buffer = new byte [size];
//Gl.glReadPixels (0, 0, video_width, video_height, Gl.GL_RGB, Gl.GL_UNSIGNED_BYTE, buffer);
// Note: BGR order to swap bytes because Microsoft always saves BITMAPs BGR
Gl.glReadPixels (0, 0, video_width, video_height, Gl.GL_BGR, Gl.GL_UNSIGNED_BYTE, buffer);


// --------------------------------------------------------------------
System.Drawing.Imaging.PixelFormat pixelFormat = System.Drawing.Imaging.PixelFormat.Format24bppRgb;
int stride = 3 * video_width;
// 3 - since RGB is 24-bit which equals 3 bytes

unsafe {
fixed (byte * ptr = &buffer[0])
{
System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(video_width,video_height,stride,pixelFormat,(IntPtr)ptr);

System.Drawing.Imaging.ImageFormat iformat = System.Drawing.Imaging.ImageFormat.Bmp;
bmp.Save (file+".bmp",iformat);
}
}
// --------------------------------------------------------------------
// Restore original viewport
// --------------------------------------------------------------------
Gl.glViewport (0,0,video[2],video[3]);
return true;
}

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Omg tnx ill see and give it a try.

Okay tested it and im getting Index was outside the bounds of the array Exeption on line
System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(video_width, video_height, stride, pixelFormat, (IntPtr)buffer[0]); //made some changes here


I looked thoruh with steps and video_width = video[2];
video_height = video[3];
size = 3 * video_width * video_height; // both video width and height are 0 why is that ...

[Edited by - jast112 on April 22, 2008 9:51:34 AM]

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It would seem that you do not have a valid glViewPort() values. ... which may imply an invalid context. Can you be sure that when you call this method you really do have a valid gl context?

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Quote:
Original post by BionicBytes
It would seem that you do not have a valid glViewPort() values. ... which may imply an invalid context. Can you be sure that when you call this method you really do have a valid gl context?


1st Thanks for the replay.

So how to check that its valid or not?

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