在Windows下捕获屏幕图像可以有多重方法，比较简单可以调用第三方库，如Qt的屏幕截屏API就很容易调用。 在这里介绍如何用Windows API实现截屏并转换成RGB格式存储。
#include <windows.h>
//最终f的内存布局为BGRA格式，需要保证buf长度足够(>w*h*4)
void ScreenCap(void* buf, int* w, int* h)
{
HWND hDesk = GetDesktopWindow();
HDC hScreen = GetDC(hDesk);
int width = GetDeviceCaps(hScreen, HORZRES);
int height = GetDeviceCaps(hScreen, VERTRES);
if (w != 0)
*w = width;
if (h != 0)
*h = height;
HDC hdcMem = CreateCompatibleDC(hScreen);
HBITMAP hBitmap = CreateCompatibleBitmap(hScreen, width, height);
BITMAPINFOHEADER bmi = { 0 };
bmi.biSize = sizeof(BITMAPINFOHEADER);
bmi.biPlanes = 1;
bmi.biBitCount = 32;
bmi.biWidth = width;
bmi.biHeight = -height;
bmi.biCompression = BI_RGB;
bmi.biSizeImage = width*height;
SelectObject(hdcMem, hBitmap);
BitBlt(hdcMem, 0, 0, width, height, hScreen, 0, 0, SRCCOPY);
GetDIBits(hdcMem, hBitmap, 0, height, buf, (BITMAPINFO*)&bmi, DIB_RGB_COLORS);
DeleteDC(hdcMem);
ReleaseDC(hDesk, hScreen);
CloseWindow(hDesk);
DeleteObject(hBitmap);
}