Question

我不明白为什么这不起作用。在消息WM_LBUTTONDOWN上，存储指针的坐标。然后在WM_MOUSEMOVE上，如果左键按下，我希望它用原始点和鼠标所在的新点绘制一个椭圆。但是当我调试时没有任何反应。这是我的WindowProc

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
 {
PAINTSTRUCT ps;
HDC hdc;


switch (uMsg)
{

    case WM_DESTROY: 
    {
    DestroyWindow(hwnd);
    PostQuitMessage(0);
    break;

    }
    case WM_PAINT:
    {
        hdc = BeginPaint(hwnd, &ps);
        EndPaint(hwnd, &ps);
        break;
    }
    case WM_LBUTTONDOWN:
    {
        pnt.x = GET_X_LPARAM(lParam);
        pnt.y = GET_Y_LPARAM(lParam);
        break;
    }
    case WM_MOUSEMOVE:
    {
        if(wParam == MK_LBUTTON)
        {
            hdc = BeginPaint(hwnd, &ps);
            Ellipse(hdc, pnt.x, pnt.y, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)); // nothing happens
            EndPaint(hwnd, &ps);
        }
        break;
    }
    return 0;
}
   return  DefWindowProc(hwnd, uMsg, wParam, lParam);
 }

Answer 1

您尚未使窗口的任何区域无效，因此BeginPaint不会执行任何操作。您应该将该点存储在WM_MOUSEMOVE上（与pnt类似的结构），并在那时调用InvalidateRect()。然后，在WM_PAINT中进行绘画。有关详细信息，请参阅此link。

Answer 2

尝试使用以下代码：

static POINT begin, end;
static BOOL drawing = false;

// ...


case WM_PAINT:
    hdc = BeginPaint(hWnd, &ps);
    if (drawing)
        Ellipse(hdc, begin.x, begin.y, end.x, end.y);
    EndPaint(hWnd, &ps);
    break;

case WM_LBUTTONDOWN:
    begin.x = GET_X_LPARAM(lParam);
    begin.y = GET_Y_LPARAM(lParam);
    SetCapture(hWnd);
    drawing = true;
    break;

case WM_LBUTTONUP:
    ReleaseCapture();
    drawing = false;
    break;

case WM_MOUSEMOVE:
    end.x = GET_X_LPARAM(lParam);
    end.y = GET_Y_LPARAM(lParam);
    { 
        RECT invalid = {begin.x, begin.y, end.x, end.y};
        InvalidateRect(hWnd, &invalid, true);
    }
    break;

调整椭圆大小

2 个答案: