win32之bitmap篇

先讲一下LoadBitmap的用法，代码如下：

    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(hwnd,&ps);
    HDC hMemDC = CreateCompatibleDC(hdc);
    HBITMAP hBitmap = LoadBitmap(g_hIntance,MAKEINTRESOURCE(IDB_BITMAP1));
    HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemDC,hBitmap);

    //把HBITMAP转换成BITMAP，从而获取位图的宽高。
    BITMAP bmp;
    GetObject(hBitmap, sizeof(BITMAP), &bmp);
    BitBlt(hdc,,,bmp.bmWidth,bmp.bmHeight,hMemDC,,,SRCCOPY);

    SelectObject(hMemDC,hOldBitmap);
    DeleteObject(hBitmap);
    DeleteDC(hMemDC);
    EndPaint(hwnd,&ps);    

BitBlt的作用是把hMemDC上的内容拷贝到hdc上，不进行缩放，但是可以位移。

如果想要缩放，可以使用StretchBlt,以下这个例子比较有趣，是把整个屏幕绘制到窗口中。

    PAINTSTRUCT ps;
    HDC hdcClient = BeginPaint(hwnd, &ps);
    HDC hdcScreen = CreateDC(TEXT("DISPLAY"), NULL, NULL, NULL);
    RECT rtClient;
    int scrWidth = GetSystemMetrics(SM_CXSCREEN);
    int scrHeight = GetSystemMetrics(SM_CYSCREEN);
    GetClientRect(hwnd,&rtClient);
    StretchBlt(hdcClient,,,rtClient.right,rtClient.bottom,
        hdcScreen,,,scrWidth,scrHeight,SRCCOPY);

    DeleteDC(hdcScreen);
    EndPaint(hwnd, &ps);