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Usando retângulos (Windows GDI)

O exemplo nesta seção ilustra como usar as funções de retângulo. Ele consiste no procedimento de janela main de um aplicativo que permite que o usuário mova e dimensione um bitmap.

Quando o aplicativo é iniciado, ele desenha um bitmap de 32 pixels por 32 pixels no canto superior esquerdo da tela. O usuário pode mover o bitmap arrastando-o. Para dimensionar o bitmap, o usuário cria um retângulo de destino arrastando o mouse e arrasta o bitmap e o "solta" no retângulo de destino. O aplicativo responde copiando o bitmap para o retângulo de destino.

O procedimento de janela que permite que o usuário mova e dimensione o bitmap é dado no exemplo a seguir.

LRESULT CALLBACK MainWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) 
{ 
    HDC hdc;                 // device context (DC) for window  
    RECT rcTmp;              // temporary rectangle  
    PAINTSTRUCT ps;          // paint data for BeginPaint and EndPaint  
    POINT ptClientUL;        // client area upper left corner  
    POINT ptClientLR;        // client area lower right corner  
    static HDC hdcCompat;    // DC for copying bitmap  
    static POINT pt;         // x and y coordinates of cursor  
    static RECT rcBmp;       // rectangle that encloses bitmap  
    static RECT rcTarget;    // rectangle to receive bitmap  
    static RECT rcClient;    // client-area rectangle  
    static BOOL fDragRect;   // TRUE if bitmap rect. is dragged  
    static HBITMAP hbmp;     // handle of bitmap to display  
    static HBRUSH hbrBkgnd;  // handle of background-color brush  
    static COLORREF crBkgnd; // color of client-area background  
    static HPEN hpenDot;     // handle of dotted pen  
 
    switch (uMsg) 
    { 
        case WM_CREATE: 
 
            // Load the bitmap resource.  
 
            hbmp = LoadBitmap(hinst, MAKEINTRESOURCE(1)); 
 
            // Create a device context (DC) to hold the bitmap.  
            // The bitmap is copied from this DC to the window's DC  
            // whenever it must be drawn.  
 
            hdc = GetDC(hwnd); 
            hdcCompat = CreateCompatibleDC(hdc); 
            SelectObject(hdcCompat, hbmp); 
 
            // Create a brush of the same color as the background  
            // of the client area. The brush is used later to erase  
            // the old bitmap before copying the bitmap into the  
            // target rectangle.  
 
            crBkgnd = GetBkColor(hdc); 
            hbrBkgnd = CreateSolidBrush(crBkgnd); 
            ReleaseDC(hwnd, hdc); 
 
            // Create a dotted pen. The pen is used to draw the  
            // bitmap rectangle as the user drags it.  
 
            hpenDot = CreatePen(PS_DOT, 1, RGB(0, 0, 0)); 
 
            // Set the initial rectangle for the bitmap. Note that  
            // this application supports only a 32- by 32-pixel  
            // bitmap. The rectangle is slightly larger than the  
            // bitmap.  
 
            SetRect(&rcBmp, 1, 1, 34, 34); 
            return 0; 
 
        case WM_PAINT: 
 
            // Draw the bitmap rectangle and copy the bitmap into  
            // it. The 32-pixel by 32-pixel bitmap is centered  
            // in the rectangle by adding 1 to the left and top  
            // coordinates of the bitmap rectangle, and subtracting 2  
            // from the right and bottom coordinates.  
 
            BeginPaint(hwnd, &ps); 
            Rectangle(ps.hdc, rcBmp.left, rcBmp.top, 
                rcBmp.right, rcBmp.bottom); 
            StretchBlt(ps.hdc, rcBmp.left + 1, rcBmp.top + 1, 
                (rcBmp.right - rcBmp.left) - 2, 
                (rcBmp.bottom - rcBmp.top) - 2, hdcCompat, 
                0, 0, 32, 32, SRCCOPY); 
            EndPaint(hwnd, &ps); 
            break; 
 
        case WM_MOVE: 
        case WM_SIZE: 
 
            // Convert the client coordinates of the client-area  
            // rectangle to screen coordinates and save them in a  
            // rectangle. The rectangle is passed to the ClipCursor  
            // function during WM_LBUTTONDOWN processing.  
 
            GetClientRect(hwnd, &rcClient); 
            ptClientUL.x = rcClient.left; 
            ptClientUL.y = rcClient.top; 
            ptClientLR.x = rcClient.right; 
            ptClientLR.y = rcClient.bottom; 
            ClientToScreen(hwnd, &ptClientUL); 
            ClientToScreen(hwnd, &ptClientLR); 
            SetRect(&rcClient, ptClientUL.x, ptClientUL.y, 
                ptClientLR.x, ptClientLR.y); 
            return 0; 
 
        case WM_LBUTTONDOWN: 
 
            // Restrict the mouse cursor to the client area. This  
            // ensures that the window receives a matching  
            // WM_LBUTTONUP message.  
 
            ClipCursor(&rcClient); 
 
            // Save the coordinates of the mouse cursor.  
 
            pt.x = (LONG) LOWORD(lParam); 
            pt.y = (LONG) HIWORD(lParam); 
 
            // If the user has clicked the bitmap rectangle, redraw  
            // it using the dotted pen. Set the fDragRect flag to  
            // indicate that the user is about to drag the rectangle.  
 
            if (PtInRect(&rcBmp, pt)) 
            { 
                hdc = GetDC(hwnd); 
                SelectObject(hdc, hpenDot); 
                Rectangle(hdc, rcBmp.left, rcBmp.top, rcBmp.right, 
                    rcBmp.bottom); 
                fDragRect = TRUE; 
                ReleaseDC(hwnd, hdc); 
            } 
            return 0; 
 
        case WM_MOUSEMOVE: 
 
            // Draw a target rectangle or drag the bitmap rectangle,  
            // depending on the status of the fDragRect flag.  
 
            if ((wParam && MK_LBUTTON) 
                    && !fDragRect) 
            {
                // Set the mix mode so that the pen color is the  
                // inverse of the background color. The previous  
                // rectangle can then be erased by drawing  
                // another rectangle on top of it.  
 
                hdc = GetDC(hwnd); 
                SetROP2(hdc, R2_NOTXORPEN); 
 
                // If a previous target rectangle exists, erase  
                // it by drawing another rectangle on top of it.  
 
                if (!IsRectEmpty(&rcTarget)) 
                { 
                    Rectangle(hdc, rcTarget.left, rcTarget.top, 
                        rcTarget.right, rcTarget.bottom); 
                } 
 
                // Save the coordinates of the target rectangle. Avoid  
                // invalid rectangles by ensuring that the value of  
                // the left coordinate is lesser than the  
                // right coordinate, and that the value of the top 
                // coordinate is lesser than the bottom coordinate. 
 
                if ((pt.x < (LONG) LOWORD(lParam)) && 
                        (pt.y > (LONG) HIWORD(lParam))) 
                {
                    SetRect(&rcTarget, pt.x, HIWORD(lParam), 
                        LOWORD(lParam), pt.y); 
                }
                else if ((pt.x > (LONG) LOWORD(lParam)) && 
                        (pt.y > (LONG) HIWORD(lParam))) 
                {
                    SetRect(&rcTarget, LOWORD(lParam), 
                        HIWORD(lParam), pt.x, pt.y); 
                }
                else if ((pt.x > (LONG) LOWORD(lParam)) && 
                        (pt.y < (LONG) HIWORD(lParam))) 
                { 
                    SetRect(&rcTarget, LOWORD(lParam), pt.y, 
                        pt.x, HIWORD(lParam)); 
                }
                else 
                {
                    SetRect(&rcTarget, pt.x, pt.y, LOWORD(lParam), 
                        HIWORD(lParam)); 
                }
 
                // Draw the new target rectangle.  
 
                Rectangle(hdc, rcTarget.left, rcTarget.top, 
                    rcTarget.right, rcTarget.bottom); 
                ReleaseDC(hwnd, hdc); 
            } 
            else if ((wParam && MK_LBUTTON) 
                    && fDragRect) 
            {
 
                // Set the mix mode so that the pen color is the  
                // inverse of the background color.  
 
                hdc = GetDC(hwnd); 
                SetROP2(hdc, R2_NOTXORPEN); 
 
                // Select the dotted pen into the DC and erase  
                // the previous bitmap rectangle by drawing  
                // another rectangle on top of it.  
 
                SelectObject(hdc, hpenDot); 
                Rectangle(hdc, rcBmp.left, rcBmp.top, 
                    rcBmp.right, rcBmp.bottom); 
 
                // Set the new coordinates of the bitmap rectangle,  
                // then redraw it.  
 
                OffsetRect(&rcBmp, LOWORD(lParam) - pt.x, 
                    HIWORD(lParam) - pt.y); 
                Rectangle(hdc, rcBmp.left, rcBmp.top, 
                    rcBmp.right, rcBmp.bottom); 
                ReleaseDC(hwnd, hdc); 
 
                // Save the coordinates of the mouse cursor.  
 
                pt.x = (LONG) LOWORD(lParam); 
                pt.y = (LONG) HIWORD(lParam); 
            } 
            return 0; 
 
        case WM_LBUTTONUP: 
 
            // If the bitmap rectangle and target rectangle  
            // intersect, copy the bitmap into the target  
            // rectangle. Otherwise, copy the bitmap into the  
            // rectangle bitmap at its new location.  
 
            if (IntersectRect(&rcTmp, &rcBmp, &rcTarget)) 
            { 
 
                // Erase the bitmap rectangle by filling it with  
                // the background color.  
 
                hdc = GetDC(hwnd); 
                FillRect(hdc, &rcBmp, hbrBkgnd); 
 
                // Redraw the target rectangle because the part  
                // that intersected with the bitmap rectangle was  
                // erased by the call to FillRect.  
 
                Rectangle(hdc, rcTarget.left, rcTarget.top, 
                    rcTarget.right, rcTarget.bottom); 
 
                // Copy the bitmap into the target rectangle.  
 
                StretchBlt(hdc, rcTarget.left + 1, rcTarget.top + 1, 
                    (rcTarget.right - rcTarget.left) - 2, 
                    (rcTarget.bottom - rcTarget.top) - 2, hdcCompat, 
                    0, 0, 32, 32, SRCCOPY); 
 
                // Copy the target rectangle to the bitmap  
                // rectangle, set the coordinates of the target  
                // rectangle to 0, then reset the fDragRect flag.  
 
                CopyRect(&rcBmp, &rcTarget); 
                SetRectEmpty(&rcTarget); 
                ReleaseDC(hwnd, hdc); 
                fDragRect = FALSE; 
            } 
 
            else if (fDragRect) 
            { 
 
                // Draw the bitmap rectangle, copy the bitmap into  
                // it, and reset the fDragRect flag.  
 
                hdc = GetDC(hwnd); 
                Rectangle(hdc, rcBmp.left, rcBmp.top, 
                    rcBmp.right, rcBmp.bottom); 
                StretchBlt(hdc, rcBmp.left + 1, rcBmp.top + 1, 
                    (rcBmp.right - rcBmp.left) - 2, 
                    (rcBmp.bottom - rcBmp.top) - 2, hdcCompat, 
                    0, 0, 32, 32, SRCCOPY); 
                ReleaseDC(hwnd, hdc); 
                fDragRect = FALSE; 
            } 
 
            // Release the mouse cursor.  
 
            ClipCursor((LPRECT) NULL); 
            return 0; 
 
        case WM_DESTROY: 
 
            // Destroy the background brush, compatible bitmap,  
            // and the bitmap.  
 
            DeleteObject(hbrBkgnd); 
            DeleteDC(hdcCompat); 
            DeleteObject(hbmp); 
            PostQuitMessage(0); 
            break; 
 
        default: 
            return DefWindowProc(hwnd, uMsg, wParam, lParam); 
    } 
    return (LRESULT) NULL; 
}