Win32绘制可拖动矩形

Question

Win32绘制可拖动矩形

3

我正在尝试通过左键单击一个点并拖动来绘制矩形，在您拖动时，矩形会形成预览，以显示矩形的外观。这个功能很好用，但是当我拖回到一个较小的矩形时，旧矩形仍然存在。

    case WM_PAINT:
    hdc = BeginPaint(hWnd, &ps);
    // TODO: Add any drawing code here...

    if(painting)
    {



            HPEN greenPen=CreatePen(PS_SOLID, 1, RGB(0,255,0));
            SelectObject(hdc,greenPen);
            Rectangle(hdc, x1, y1, x2, y2);

    }


    EndPaint(hWnd, &ps);
    break;
case WM_LBUTTONDOWN:
    painting=true;
    x1=LOWORD(lParam);
    y1=HIWORD(lParam);
    InvalidateRect(hWnd, NULL ,false);
    break;
case WM_MOUSEMOVE:



        x2=LOWORD(lParam);
        y2=HIWORD(lParam);

        InvalidateRect(hWnd, NULL ,false);


    break;
case WM_LBUTTONUP:

    painting=false;
    break;

- user1788175

当您仍按住鼠标按钮时？ - Aesthete

当我仍然按住鼠标时，我知道为什么会发生这种情况，但是有没有办法去掉那些旧的矩形呢？谢谢。 - user1788175

使用InvalidateRect函数，将最后一个参数设置为TRUE。 - cha

这是真正的代码吗？如果是，那么GDI对象存在问题。如果不销毁greenPen，很快就会用完GDI对象。此外，在SelectObject之后存储前一个对象并在完成后将其返回到DC是个好主意。 - cha

这不是真正的代码，但还是谢谢。我已经将其设置为true，但这意味着一旦我绘制另一个矩形，旧矩形就会被删除。我该如何存储先前的对象？（矩形） - user1788175

1个回答

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- enhzflep · Accepted Answer

@user1788175 - just use a RECT struct. When the drawing starts, you set the left & top members to the x,y pos of the mouse. When the mouse is released, set the right,bottom members. Swap left,right if necessary, to ensure that left

Here's some code ripped from a class I wrote to deal with with selection rectangles. You can ignore the normalize code - it just converts the pixel coordinates to ones in the range [0..1], so I can draw the selection on a scaled-down version of the image, yet still select the same region if the image is shown at a different scale. My images were 4944x6992, so I had to display a scaled-down version of them.

LRESULT CALLBACK cSelBoxImg::WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    RECT mappedRect, tmpRect, myRect;
    HBRUSH myBrush;
    BITMAP bm;
    PAINTSTRUCT ps;
    HDC mDC;
    HBITMAP tmpBmp;

    switch (uMsg)
    {
    case WM_LBUTTONDOWN:
        if (bMouseSelectionEnabled)
        {
            bRubberBanding = true;
            mouseClickDownPos.x = LOWORD(lParam);
            mouseClickDownPos.y = HIWORD(lParam);

            curMousePos = mouseClickDownPos;
            selectionRect.left = min(curMousePos.x, mouseClickDownPos.x);
            selectionRect.right = max(curMousePos.x, mouseClickDownPos.x);
            selectionRect.top = min(curMousePos.y, mouseClickDownPos.y);
            selectionRect.bottom = max(curMousePos.y, mouseClickDownPos.y);
            normalizeSelRect();
            InvalidateRect(mHwnd, NULL, isBkgTransparent);
            PostMessage(GetParent(hWnd),  WM_COMMAND, GetDlgCtrlID(hWnd), (LPARAM)hWnd);
        }
        return 1;

    case WM_LBUTTONUP:
        if (bMouseSelectionEnabled)
            if (bRubberBanding)
            {
                bRubberBanding = false;
                mouseClickUpPos.x = LOWORD(lParam);
                mouseClickUpPos.y = HIWORD(lParam);

                selectionRect.left = min(mouseClickUpPos.x, mouseClickDownPos.x);
                selectionRect.right = max(mouseClickUpPos.x, mouseClickDownPos.x);
                selectionRect.top = min(mouseClickUpPos.y, mouseClickDownPos.y);
                selectionRect.bottom = max(mouseClickUpPos.y, mouseClickDownPos.y);

                normalizeSelRect();
                InvalidateRect(mHwnd, NULL, isBkgTransparent);
                PostMessage(GetParent(hWnd),  WM_COMMAND, GetDlgCtrlID(hWnd), (LPARAM)hWnd);
            }
        return 1;

    case WM_MOUSEMOVE:
        if (bMouseSelectionEnabled)
            if (bRubberBanding)
            {
                curMousePos.x = LOWORD(lParam);
                curMousePos.y = HIWORD(lParam);

                selectionRect.left = min(curMousePos.x, mouseClickDownPos.x);
                selectionRect.right = max(curMousePos.x, mouseClickDownPos.x);
                selectionRect.top = min(curMousePos.y, mouseClickDownPos.y);
                selectionRect.bottom = max(curMousePos.y, mouseClickDownPos.y);
                //                UpdateWindow(hWnd);
                //RedrawWindow(hWnd, NULL, NULL, RDW_UPDATENOW);
                normalizeSelRect();
                InvalidateRect(hWnd, NULL, false);
                PostMessage(GetParent(hWnd),  WM_COMMAND, GetDlgCtrlID(hWnd), (LPARAM)hWnd);
                //       printf("Message posted\n");
            }
        return 0;

    case WM_PAINT:

        mDC = BeginPaint(hWnd, &ps);

        GetClientRect(hWnd, &tmpRect);
    //        GetObject(mBmp, sizeof(bm), &bm);
        mappedRect.left = mLeft * tmpRect.right;
        mappedRect.right = mRight * tmpRect.right;
        mappedRect.top = mTop * tmpRect.bottom;
        mappedRect.bottom = mBottom * tmpRect.bottom;

        displayImage();
        if  (mBmp) drawRect(mDC, mappedRect, RGB(0,0,255));
        DeleteObject(tmpBmp);
        EndPaint(hWnd, &ps);

        return 0;

    case WM_ERASEBKGND:
        if (isBkgTransparent)
        {
            GetClientRect(hWnd, &myRect);
            myBrush = (HBRUSH) GetWindowLong(hWnd, GCL_HBRBACKGROUND);
            FillRect((HDC)wParam, &myRect, myBrush);
            printf("background cleared\n");
        }
        return true;

    case WM_SETCURSOR:
        SetCursor(mCursor);
        return true;
    }
    return DefWindowProc(hWnd, uMsg, wParam, lParam);
}