HDC和Memory DC是否不同？

Question

我正在学习windows winapi中的双缓冲。当我直接使用DrawText函数在HDC上绘制文本时，它就像在代码下一样工作得很好。

case WM_PAINT:
hDC = BeginPaint(hwnd,&ps);
DrawText(hDC,"test",4,&rt,DT_CENTER | DT_WORDBREAK);
DeleteDC(hMemDC);
ReleaseDC(hwnd,hDC);
EndPaint(hwnd,&ps);
break;

但是，我想使用双缓冲，所以我做了内存dc和bitblt函数。在代码下面，它不工作。我可以显示白色的空白屏幕。

case WM_PAINT:
hDC = BeginPaint(hwnd,&ps);
hMemDC = CreateCompatibleDC(hDC);
//GetClientRect(hwnd, &crt);
//hBitmap = CreateCompatibleBitmap(hDC, crt.right, crt.bottom);
//OldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);
DrawText(hMemDC,"test",4,&rt,DT_CENTER | DT_WORDBREAK);
BitBlt(hDC,0,0,800,800,hMemDC,0,0,SRCCOPY);
DeleteDC(hMemDC);
ReleaseDC(hwnd,hDC);
EndPaint(hwnd,&ps);
break;

memory dc是否与原始dc不同？如果我使用CreateCompatibleBitmap函数，它工作得很好。我错过了什么概念？网站是否有组织良好的网站？

Answer 1

典型的非双缓冲绘图例程如下所示：

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);
        RECT rcWnd;
        GetClientRect(hWnd, &rcWnd);
        
        {
            DrawText(hdc, _T("Hello, world!"), -1,
                &rcWnd, DT_CENTER | DT_VCENTER | DT_SINGLELINE);
        }
        
        EndPaint(hWnd, &ps);
    }
    break;

典型的双缓冲绘图例程如下所示：

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);
        RECT rcWnd;
        GetClientRect(hWnd, &rcWnd);

        {
            const int width = rcWnd.right - rcWnd.left
            const int height = rcWnd.bottom - rcWnd.top;

            // create a new DC based on the target HDC
            HDC hDCMem = CreateCompatibleDC(hdc);
            // create a bitmap that is compatible with the target DC
            HBITMAP hMemBmp = CreateCompatibleBitmap(hdc, width, height);
            // select the new bitmap in to the DC, saving the old bitmap
            HBITMAP hOldBmp = (HBITMAP)SelectObject(hDCMem, hMemBmp);

            // do your drawing
            HBRUSH hBr = CreateSolidBrush(RGB(255, 255, 255));
            FillRect(hDCMem, &rcWnd, hBr);
            DeleteObject(hBr);
            DrawText(hDCMem, _T("Hello, world!"), -1,
                &rcWnd, DT_CENTER | DT_VCENTER | DT_SINGLELINE);

            // copy all the bits from our new DC over to the target DC
            BitBlt(hdc, rcWnd.left, rcWnd.top, width, height, hDCMem, 0, 0, SRCCOPY);
            // select the original bitmap the DC came with
            SelectObject(hDCMem, hOldBmp);
            // delete our bitmap
            DeleteObject(hMemBmp);
            // delete the DC
            DeleteDC(hDCMem);
        }
        
        EndPaint(hWnd, &ps);
    }
    break;
case WM_ERASEBKGND:
    // since we are drawing the entire area because we are double-buffering, there is
    // no need to erase the background. This will speed up your drawing.
    return TRUE;

HDC对象都是一样的--当您在内存中创建另一个对象时，不会发生任何特殊的事情。我是说，它们都在记忆中，真的。您只是在创建另一个画布来进行绘图，然后在一次拍摄中复制该画布。