如何避免GDI过大屏幕闪烁

Question

我对用GDI绘制图形有点陌生..。

我做了一个油漆程序，它工作的很好，只是它引起了许多恼人的屏幕闪烁。我承认我的油漆代码并没有真正优化(缺乏时间)，但它也不应该是超级低效的，所以我很困惑。

我所做的基本上是在init上创建一个兼容的DC，然后创建一个兼容的位图。然后，我选择它到兼容的DC，并绘制到兼容的DC。然后我使用BitBlit()将其复制到hDC窗口..。

有人能告诉我屏幕撕裂的可能原因吗？编辑:顺便说一下，屏幕闪烁只发生在路径的绘制过程中(在路径被绘制到hMemDC之前，它会被绘制到窗口的hDC )。

代码示例：(编辑:如果您需要看到更多您认为相关的代码，请批注，我将编辑)

路径:DrawTo(HDC)

bool Path::DrawTo(HDC hDC)
{
    if(hDC == NULL || m_PointVector.size() <= 0) {
        return false;
    }

    switch (m_Tool) {
    case Tool_Pen:
        {
            Point2D p = m_PointVector.at(0);

            if(m_PointVector.size() > 1) {
                HPEN oldPen = (HPEN)SelectObject(hDC,m_hPen);

                MoveToEx(hDC, p.x, p.y, nullptr);

                for(UINT i = 1; i < m_PointVector.size(); ++i) {
                    p = m_PointVector.at(i);
                    LineTo(hDC,p.x,p.y);
                }

                SelectObject(hDC,oldPen);
                break;
            } //else

            SetPixel(hDC,p.x-1,p.y,m_Col);
            SetPixel(hDC,p.x,p.y,m_Col);
            SetPixel(hDC,p.x+1,p.y,m_Col);
            SetPixel(hDC,p.x,p.y-1,m_Col);
            SetPixel(hDC,p.x,p.y+1,m_Col);
            break;
        }
    case Tool_Line:
        {
            if(m_PointVector.size() > 1) {
                Point2D p = m_PointVector.at(0);
                HPEN oldPen = (HPEN)SelectObject(hDC,m_hPen);

                MoveToEx(hDC, p.x, p.y, nullptr);

                for(UINT i = 1; i < m_PointVector.size(); ++i) {
                    p = m_PointVector.at(i);
                    LineTo(hDC,p.x,p.y);
                }

                SelectObject(hDC,oldPen);
            }
            break;
        }
    case Tool_Ellipse:
        {
            if(m_PointVector.size() > 1) {
                HPEN oldPen = (HPEN)SelectObject(hDC,m_hPen);
                SelectObject(hDC,m_hBrush);

                Point2D p1 = m_PointVector.at(0);
                Point2D p2 = m_PointVector.at(1);

                if(p1.x > p2.x) {
                    int iTemp = p1.x;
                    p1.x = p2.x;
                    p2.x = iTemp;
                }
                if(p1.y > p2.y) {
                    int iTemp = p1.y;
                    p1.y = p2.y;
                    p2.y = iTemp;
                }

                Ellipse(hDC,p1.x,p1.y,p2.x,p2.y);

                SelectObject(hDC,oldPen);
            }
            break;
        }
    case Tool_Rectangle:
        {
            if(m_PointVector.size() > 1) {
                HPEN oldPen = (HPEN)SelectObject(hDC,m_hPen);
                SelectObject(hDC,m_hBrush);

                Point2D p1 = m_PointVector.at(0);
                Point2D p2 = m_PointVector.at(1);

                if(p1.x > p2.x) {
                    int iTemp = p1.x;
                    p1.x = p2.x;
                    p2.x = iTemp;
                }
                if(p1.y > p2.y) {
                    int iTemp = p1.y;
                    p1.y = p2.y;
                    p2.y = iTemp;
                }

                Rectangle(hDC,p1.x,p1.y,p2.x,p2.y);

                SelectObject(hDC,oldPen);
            }
            break;
        }
    case Tool_LineTrack:
        {
            HPEN oldPen = (HPEN)SelectObject(hDC,m_hPen);
            SelectObject(hDC,m_hBrush);

            int vSize = (int)m_PointVector.size();
            Point2D p = m_PointVector.at(0);

            if (vSize <= 1) {
                Ellipse(hDC,p.x-10,p.y-10,p.x+10,p.y+10);
            }
            else {
                //draw LineTrack
                Point2D pTemp = m_PointVector.at(1);
                MoveToEx(hDC,p.x,p.y,nullptr);

                for (int i = 1; i < vSize; ++i) {
                    p = m_PointVector.at(i);
                    pTemp = m_PointVector.at(i-1);
                    LineTo(hDC,p.x,p.y);
                    Ellipse(hDC,pTemp.x-10,pTemp.y-10,pTemp.x+10,pTemp.y+10);
                }

                Ellipse(hDC,p.x-10,p.y-10,p.x+10,p.y+10);
            }

            SelectObject(hDC,oldPen);
            break;
        }
    }

    return true;
}

WndProc(HWND，UINT，WPARAM，LPARAM)

LRESULT MyApp::WndProc(HWND hWnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
    if(iMsg == WM_CREATE)
    {
        CREATESTRUCT *pCS = (CREATESTRUCT*)lParam;
        SetWindowLongPtr(hWnd, GWLP_USERDATA, (LONG)pCS->lpCreateParams);

    }
    else
    {
        //retrieve the stored "this" pointer
        MyApp* pApp = (MyApp*)GetWindowLongPtr(hWnd, GWLP_USERDATA);

        switch (iMsg)
        {
            case WM_PAINT:
                {
                pApp->Paint();
                return 0;
                }

            case WM_COMMAND:
            {
                int wmId    = LOWORD(wParam);
                int wmEvent = HIWORD(wParam);

                // Parse the menu selections:
                switch (wmId)
                {
                case IDM_NEW:
                    {
                        ////
                        return 0;
                    }
                    return 0;
                case IDM_LOAD:
                    {
                        //////
                        return 0;
                    }
                case IDM_SAVE:
                    {
                    //////
                    return 0;
                    }
                case IDM_SAVEAS:
                    {
                        //////
                        return 0;
                    }
                case IDM_COLOURMAIN:
                    {
                        COLORREF col;
                        if(MyWin32Funcs::OnColorPick(col)) {
                            pApp->m_pPath->SetColor1(col);
                        }
                    return 0;
                    }
                case IDM_COLOURSECONDARY:
                    {
                    COLORREF col;
                        if(MyWin32Funcs::OnColorPick(col)) {
                            pApp->m_pPath->SetColor2(col);
                        }
                    return 0;
                    }
                case IDM_PEN:
                    {
                        pApp->m_pPath->SetTool(Tool_Pen);
                        return 0;
                    }
                case IDM_LINE:
                    {
                        pApp->m_pPath->SetTool(Tool_Line);
                        return 0;
                    }
                case IDM_ELLIPSE:
                    {
                        pApp->m_pPath->SetTool(Tool_Ellipse);
                        return 0;
                    }
                case IDM_RECTANGLE:
                    {
                        pApp->m_pPath->SetTool(Tool_Rectangle);
                        return 0;
                    }
                case IDM_LINETRACK:
                    {
                        pApp->m_pPath->SetTool(Tool_LineTrack);
                        return 0;
                    }
                default:
                    {
                    //////
                    return 0;
                    }
                }
            }

            case WM_LBUTTONUP:
                {
                    //////
                    Point2D p;
                    p.x = LOWORD(lParam); 
                    p.y = HIWORD(lParam);

                    switch(pApp->m_pPath->GetTool()) {
                        case Tool_Pen:
                            {
                                pApp->m_bPaintToBitmap = true;
                                InvalidateRect(pApp->m_hWnd,NULL,true);
                                break;
                            }
                        case Tool_Ellipse:
                            {
                                pApp->m_bPaintToBitmap = true;
                                InvalidateRect(pApp->m_hWnd,NULL,true);
                                break;
                            }
                        case Tool_Rectangle:
                            {
                                pApp->m_bPaintToBitmap = true;
                                InvalidateRect(pApp->m_hWnd,NULL,true);
                                break;
                            }
                        case Tool_Line:
                            {
                                pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                                InvalidateRect(pApp->m_hWnd,NULL,false);
                                break;
                            }
                        case Tool_LineTrack:
                            {
                                pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                                InvalidateRect(pApp->m_hWnd,NULL,false);
                                break;
                            }
                    }

                    return 0;
                }

            case WM_RBUTTONUP:
                {
                    //////
                    int x = LOWORD(lParam);
                    int y = HIWORD(lParam);

                    switch(pApp->m_pPath->GetTool()) {
                        case Tool_Line:
                            {
                                pApp->m_bPaintToBitmap = true;
                                InvalidateRect(pApp->m_hWnd,NULL,true);
                                break;
                            }
                        case Tool_LineTrack:
                            {
                                pApp->m_bPaintToBitmap = true;
                                InvalidateRect(pApp->m_hWnd,NULL,true);
                                break;
                            }
                    }

                    return 0;
                }
            case WM_LBUTTONDOWN:
                {
                    Point2D p;
                    p.x = LOWORD(lParam);
                    p.y = HIWORD(lParam);
                    switch(pApp->m_pPath->GetTool()) {
                    case Tool_Pen:
                        pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                        InvalidateRect(pApp->m_hWnd,NULL,false);
                        break;
                    }
                }
            case WM_MOUSEMOVE:
                {
                    Point2D p;
                    p.x = LOWORD(lParam);
                    p.y = HIWORD(lParam);
                    if (wParam & MK_LBUTTON) {
                        switch(pApp->m_pPath->GetTool()) {
                        case Tool_Pen:
                            {
                            pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                            InvalidateRect(pApp->m_hWnd,NULL,false);
                            break;
                            }
                        case Tool_Ellipse:
                            {
                            if( pApp->m_pPath->GetLen() >= 1) {
                                pApp->m_pPath->SetPointAt(1,p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                            }
                            else {
                                pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                            }
                            InvalidateRect(pApp->m_hWnd,NULL,false);
                            break;
                            }
                        case Tool_Rectangle:
                            {
                            if( pApp->m_pPath->GetLen() >= 1) {
                                pApp->m_pPath->SetPointAt(1,p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                            }
                            else {
                                pApp->m_pPath->AddPoint(p,pApp->m_pBitmapPainter->GetBmpSize(),pApp->m_pBitmapPainter->GetBmpOffset());
                            }
                            InvalidateRect(pApp->m_hWnd,NULL,false);
                            break;
                            }
                        }
                    }

                    return 0;
                }

            case WM_CLOSE:
                {
                    //////
                                return 0;
                            }
                        }
                    PostQuitMessage(0);
                    return 0;
                }
        }
    }
    return DefWindowProc (hWnd, iMsg, wParam, lParam) ;
}

MyApp::Paint()

void MyApp::Paint()
{
    BeginPaint(m_hWnd,&m_PaintStruct);
    if (m_bPaintToBitmap) {
        Point2D p;
        p.x = BMPXOFFSET;
        p.y = BMPYOFFSET;
        m_pPath->Offset(p);
        m_pPath->DrawTo(m_pBitmapPainter->GetMemDC());
        m_pPath->ClrPath();
        m_pBitmapPainter->Paint(); //this is where BitBlt() occurs
        m_bPaintToBitmap = false;
        if(m_pBitmapPainter->IsAdjusted() == false) {
            m_pBitmapPainter->SetbAdjusted(true);
        }
    }
    else {
        m_pBitmapPainter->Paint(); //this is where BitBlt() occurs
        m_pPath->DrawTo(m_hDC);
    }
    EndPaint(m_hWnd,&m_PaintStruct);
}

任何帮助都将不胜感激。

Answer 1

我觉得你看到的是闪烁而不是撕裂。为了最小化闪烁，您的WM_PAINT应该精确地写入窗口DC一次。通常，这个操作是一个BitBlt。

HDC hdc = BeginPaint(m_hwnd, &m_PaintStruct);
... paint to bitmap ...
BitBlt(hdc, ...); // blt from bitmap to screen
EndPaint(m_hwnd, &m_PaintStruct);

如果您在多个步骤中绘制到窗口DC，则打开该窗口以进行闪烁。

您对问题的描述与代码不匹配。在您的描述中，您说您正在从兼容的DC闪到窗口hDC。但是在您的代码中，BitBlt后面是一个m_pPath->DrawTo(m_hDC)。如果在DrawTo期间发生刷新，则屏幕将使用部分绘制的视图刷新，从而导致闪烁。

Answer 2

如果要绘制整个工作区，则重写WM_ERASEBKGND，然后只返回TRUE。这将减少闪烁。

正如其他人指出的那样，请使用WM_PAINT提供的WM_PAINT，因为它可能包含剪辑区域，以及其他可能优化屏幕更新的内容。

编辑如果您没有绘制整个工作区，可以在您知道WM_PAINT处理程序不会绘制的区域执行背景绘图。

Answer 3

BeginPaint给你你应该画的HDC。你是在忽视它。