Writing a CDC to a jpeg file

[robbiegregg]

Hi all
I've been trying all day to sort this out so I was hoping someone could help!!

Basically, I am trying to write the contents of a CDC to a JPEG file and I am trying to use libjpeg.lib. Below is a simplified snippet of the code I am using at present. What I am intending the code to do is to create a picture with a square and a circle and then write this to a JPEG file. It manages to create a JPEG file with the right size however it is completely black so obviously I am doing something wrong! Any help would be greatly appreciated.

Thanks very much for reading,

Robbie

(ps. I am using Visual C++ v6 and am trying to do this within a MFC dialog based project)

void CNucPlot::SaveFile()
{
	CDC myDC;
	HBITMAP myBMP;
	myDC.CreateCompatibleDC(NULL);

	//  Set pictures size;
	int Width = 500;
	int Height = 500;

	// Draw rectangle and an ellipse to myDC ..
	CBrush newColour(RGB(10,10,10));
	myDC.SelectObject(newColour);
	CPen lColourPen (PS_SOLID, 1,RGB(50,100,150));
	myDC.SelectObject(&lColourPen); // 100

	myDC.SetBkColor(RGB(255,255,255));
	myDC.Rectangle(10,20,100,90);
	CRect Rect;
	Rect.left   = 10;
	Rect.top    = 20;
	Rect.right  = 100;
	Rect.bottom = 90;
	myDC.Ellipse(Rect);

	myBMP = CreateCompatibleBitmap(myDC,Width,Height);
	SelectObject(myDC,myBMP);

	struct jpeg_compress_struct cinfo;
	struct jpeg_error_mgr jerr;
	FILE * outfile;
	JSAMPLE* scanline;
	COLORREF pixel;

	cinfo.err = jpeg_std_error(&jerr);
	jpeg_create_compress(&cinfo);

	outfile = fopen("robbie.jpg", "wb");
	if(outfile == NULL) return;

	jpeg_stdio_dest(&cinfo, outfile);
	cinfo.image_width = Width;
	cinfo.image_height = Height;
	cinfo.input_components = 3;
	cinfo.in_color_space = JCS_RGB;	
	jpeg_set_defaults(&cinfo);

	int quality = 90;
	if(quality < 0) quality = 0;
	if(quality > 100) quality = 100;

	jpeg_set_quality(&cinfo, quality, FALSE);
	jpeg_start_compress(&cinfo, TRUE);
	scanline = new JSAMPLE[Width*3];

	for(int posy = 0; posy < Height; posy++) 
	{
		for(int posx = 0; posx < Width; posx++)
		{
			pixel = GetPixel(myDC, posx, posy);
			scanline[posx*3+0] = GetRValue(pixel);
			scanline[posx*3+1] = GetGValue(pixel);
			scanline[posx*3+2] = GetBValue(pixel);

		}
		jpeg_write_scanlines(&cinfo, &scanline, 1);
	}
	jpeg_finish_compress(&cinfo);
	jpeg_destroy_compress(&cinfo);

	delete scanline;
	fclose(outfile);
}