Thread: GDI+ and double buffering

Hi everyone! I've just started using GDI+, and I've got a program which updates the graphics whenever a timer ticks. It works fine, but it flickers annoyingly. I managed to use double buffering to solve this with GDI, but I don't know how to do this in GDI+.

Here's the structure of my program:

Code:

void update (HDC hdc)
{
   Graphics graphics(hdc);
   Pen black(Color(255, 0, 0, 0), 4);
   SolidBrush red(Color(255, 255, 0, 0));
   SolidBrush blue(Color(255, 0, 0, 255));
   SolidBrush orange(Color(255, 200, 200, 0));
   graphics.DrawLine(&black, 0, 530, GetSystemMetrics(SM_CXSCREEN), 530);
   graphics.DrawLine(&black, orangex+170, 530, orangex+170, 450);
   graphics.FillEllipse(&red, x, y, 50, 50);
   graphics.FillEllipse(&blue, bluex, bluey, 10, 150);
   graphics.FillEllipse(&orange, orangex, orangey, 150, 10);
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

	HDC hdc;
    PAINTSTRUCT ps;

    switch(msg)
    {

		case WM_TIMER:
			    //calculate new coordinates for the GDI objects.
				InvalidateRect(hwnd, NULL, TRUE);
				UpdateWindow(hwnd);
			break;

		case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
	        update(hdc);
            EndPaint(hwnd, &ps);
        break;

Any help with getting rid of the flicker would be nice I appreciate it!

You do it the same way, but instead of creating HDC's and HBITMAP's you create Graphics() & Bitmap(). To double-buffer, create a Bitmap the same size as the client area, create a Graphics based on that bitmap and do your drawing to that graphics object. When you've finished drawing, DrawImage() the bitmap to the main Graphics that's wrapping the dc.

Thanks - I've changed it to this:

Code:

void update (HWND hwnd, HDC hdc)
{
   RECT rc;
   GetClientRect(hwnd, &rc);
   Bitmap buffer(rc.right, rc.bottom);
   Graphics graphicsbuf(&buffer);
   Graphics graphics(hdc);

   Pen black(Color(255, 0, 0, 0), 4);
   SolidBrush red(Color(255, 255, 0, 0));
   SolidBrush blue(Color(255, 0, 0, 255));
   SolidBrush orange(Color(255, 200, 200, 0));
   graphicsbuf.DrawLine(&black, 0, 530, GetSystemMetrics(SM_CXSCREEN), 530);
   graphicsbuf.DrawLine(&black, orangex+170, 530, orangex+170, 450);
   graphicsbuf.FillEllipse(&red, x, y, 50, 50);
   graphicsbuf.FillEllipse(&blue, bluex, bluey, 10, 150);
   graphicsbuf.FillEllipse(&orange, orangex, orangey, 150, 10);

   graphics.DrawImage(&buffer, 0, 0);
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

	HDC hdc;
    PAINTSTRUCT ps;

    switch(msg)
    {

	    case WM_COMMAND:
			switch(LOWORD(wParam))
			{
                                          //buttons which change some of the coordinates, drawn using CreateWindowEx with hwnd.
			case IDC_RIGHT:
				orangex = orangex + 20;
				break;

			case IDC_LEFT:
				orangex = orangex - 20;
				break;

			}
			break;


		case WM_TIMER:
			    //Update coordinates here
				InvalidateRect(hwnd, NULL, TRUE);
				UpdateWindow(hwnd);
			break;

		case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
	        update(hwnd, hdc);
            EndPaint(hwnd, &ps);
        break;

... but now, the flickering is even worse and it runs slower too - have I got it right (I'm guessing not!!). Thanks for your help yet again.