/* GDI Double buffer sample */

#include <windows.h>

#define SCRW        1280
#define SCRH        720

#define FPS         60

#define TM_COUNT1   101

#define LPCLASSNAME     TEXT("DoubleBufferSample")
#define WINDOW_TITLE    TEXT("Double Buffer Sample")


LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp)
{
  static HBITMAP hBitmap;
  static HBITMAP hBitmap_mask;
  static HBITMAP hBitmap_bg;
  static HBITMAP offScrnBitmap;
  static int wdw_w, wdw_h;
  static int imgw, imgh;
  static int bgw, bgh;
  static int bgx, bgy;
  static float x, y;
  static float dx, dy;

  switch (msg)
    {
    case WM_CREATE:
      // get window size
      {
        RECT rc;
        GetClientRect(hwnd, &rc);
        wdw_w = rc.right - rc.left;
        wdw_h = rc.bottom - rc.top;
      }

      // create off screen bitmap
      {
        HDC hdc;
        hdc = GetDC(hwnd);
        offScrnBitmap = CreateCompatibleBitmap(hdc, wdw_w, wdw_h);
        ReleaseDC(hwnd, hdc);    // GetDC() -> ReleaseDC()
      }

      // load bitmaps from resource
      hBitmap = LoadBitmap(((LPCREATESTRUCT)lp)->hInstance, TEXT("BALL_IMG"));
      hBitmap_mask = LoadBitmap(((LPCREATESTRUCT)lp)->hInstance, TEXT("BALL_MSK"));
      hBitmap_bg = LoadBitmap(((LPCREATESTRUCT)lp)->hInstance, TEXT("BG_IMG"));

      // get images size
      {
        BITMAP bp;

        // get ball image size
        GetObject(hBitmap, sizeof(BITMAP), &bp);
        imgw = bp.bmWidth;
        imgh = bp.bmHeight;

        // get bg image size
        GetObject(hBitmap_bg, sizeof(BITMAP), &bp);
        bgw = bp.bmWidth;
        bgh = bp.bmHeight;
      }

      // init work
      x = wdw_w / 2;
      y = wdw_h / 2;
      dx = (float)wdw_w / (float)FPS;
      dy = dx * 0.2;
      bgx = 0;
      bgy = 0;

      SetTimer(hwnd, TM_COUNT1, (int)(1000 / FPS), NULL);
      return 0;

    case WM_TIMER:
      // main loop
      x += dx;
      y += dy;

      if (x <= 0 || (x + imgw) >= wdw_w) dx *= -1;

      if (y <= 0 || (y + imgh) >= wdw_h) dy *= -1;

      bgx -= 1;
      bgy -= 1;

      if (bgx <= -(bgw)) bgx += bgw;

      if (bgy <= -(bgh)) bgy += bgh;

      if (0)
        {
          // clear background
          InvalidateRect(hwnd, NULL, TRUE);
        }
      else
        {
          // not clear background
          InvalidateRect(hwnd, NULL, FALSE);
        }

      break;

    case WM_PAINT:
      // draw window
      {
        HDC hdc, hBmpDC, hMemDC;
        PAINTSTRUCT ps;

        hdc = BeginPaint(hwnd, &ps);
        // hdc = GetDC(hwnd);

        // set off-screen bitmap
        hMemDC = CreateCompatibleDC(hdc);
        SelectObject(hMemDC, offScrnBitmap);

        // draw bg to off-screen
        hBmpDC = CreateCompatibleDC(hdc);
        SelectObject(hBmpDC, hBitmap_bg);
        {
          int by = bgy;

          while (by <= wdw_h)
            {
              int bx = bgx;

              while (bx <= wdw_w)
                {
                  BitBlt(hMemDC, bx, by, bgw, bgh, hBmpDC, 0, 0, SRCCOPY);
                  bx += bgw;
                }

              by += bgh;
            }
        }
        DeleteDC(hBmpDC);

        // draw mask to off-screen
        hBmpDC = CreateCompatibleDC(hdc);
        SelectObject(hBmpDC, hBitmap_mask);
        BitBlt(hMemDC, (int)x, (int)y, imgw, imgh, hBmpDC, 0, 0, SRCAND);
        DeleteDC(hBmpDC);

        // draw source image to off-screen
        hBmpDC = CreateCompatibleDC(hdc);
        SelectObject(hBmpDC, hBitmap);
        BitBlt(hMemDC, (int)x, (int)y, imgw, imgh, hBmpDC, 0, 0, SRCPAINT);
        DeleteDC(hBmpDC);

        // drawing to off-screen is finished

        // draw off-screen bitmap to window
        BitBlt(hdc, 0, 0, wdw_w, wdw_h, hMemDC, 0, 0, SRCCOPY);

        DeleteDC(hMemDC);     // Create*() -> DeleteDC()

        EndPaint(hwnd, &ps);
      }

      return 0;

    case WM_DESTROY:
      KillTimer(hwnd, TM_COUNT1);  // kill timer

      DeleteObject(offScrnBitmap);
      DeleteObject(hBitmap);
      DeleteObject(hBitmap_mask);
      DeleteObject(hBitmap_bg);
      PostQuitMessage(0);
      return 0;
    }

  return DefWindowProc(hwnd, msg, wp, lp);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   PSTR lpCmdLine, int nCmdShow)
{
  HWND hwnd;
  MSG msg;
  WNDCLASS winc;

  winc.style            = CS_HREDRAW | CS_VREDRAW;
  winc.lpfnWndProc      = WndProc;
  winc.cbClsExtra       = winc.cbWndExtra   = 0;
  winc.hInstance        = hInstance;
  winc.hIcon            = LoadIcon(NULL, IDI_APPLICATION);
  winc.hCursor          = LoadCursor(NULL, IDC_ARROW);
  winc.hbrBackground    = (HBRUSH)GetStockObject(WHITE_BRUSH);
  winc.lpszMenuName     = NULL;
  winc.lpszClassName    = LPCLASSNAME;

  if (!RegisterClass(&winc)) return -1;

  hwnd = CreateWindow(
    LPCLASSNAME, WINDOW_TITLE,
    WS_OVERLAPPEDWINDOW | WS_VISIBLE,
    CW_USEDEFAULT, CW_USEDEFAULT,
    SCRW, SCRH,
    NULL, NULL,
    hInstance, NULL
    );

  if (hwnd == NULL) return -1;

  while (GetMessage(&msg, NULL, 0, 0))
    {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
    }

  return msg.wParam;
}