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.

Handle WM_ERASEBKGND (just return true) and change the last param of InvalidateRect to FALSE.

If that does not work, give your graphics object more scope (ie do the drawing BEFORE you call for a paint msg and not while the screen is 'waiting' to be redrawn within the paint msg).