void CMyView::OnLButtonDown(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default pDC=GetDC(); center=point; r=rand()%46+5;//r=5~50 color=RGB(rand()%256,rand()%256,rand()%256); br.CreateSolidBrush(color); pDC->SelectObject(&br); pDC->Ellipse(center.x-r,center.y-r,center.x+r,center.y+r); br.DeleteObject(); CView::OnLButtonDown(nFlags, point); } void CMyView::OnLButtonUp(UINT nFlags, CPoint point) { // TODO: Add your message handler code here and/or call default SetTimer(1,200,NULL); CView::OnLButtonUp(nFlags, point); } void CMyView::rise() { center.y-=5; pDC=GetDC(); br.CreateSolidBrush(color); pDC->SelectObject(&br); pDC->Ellipse(center.x-r,center.y-r,center.x+r,center.y+r); br.DeleteObject(); } void CMyView::OnTimer(UINT nIDEvent) { // TODO: Add your message handler code here and/or call default if (nIDEvent==1){ CDC *pDC=GetDC(); CRect rect; GetClientRect(&rect); for(int i=0;i<5;i++){ br.CreateSolidBrush(color); pDC->SelectObject(&br); pDC->Ellipse(center.x-r,center.y-r,center.x+r,center.y+r); br.DeleteObject();} ReleaseDC(pDC); center.y-=5; }怎么改能让这个圆没有运动轨迹

要让圆没有运动轨迹，可以在每次重绘之前，先用背景色覆盖整个视图区域，然后再绘制圆。修改代码如下：

void CMyView::OnLButtonDown(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    pDC = GetDC();
    center = point;
    r = rand() % 46 + 5; //r=5~50
    color = RGB(rand() % 256, rand() % 256, rand() % 256);
    br.CreateSolidBrush(color);
    pDC->SelectObject(&br);
    pDC->Ellipse(center.x - r, center.y - r, center.x + r, center.y + r);
    br.DeleteObject();
    CView::OnLButtonDown(nFlags, point);
}

void CMyView::OnLButtonUp(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    SetTimer(1, 200, NULL);
    CView::OnLButtonUp(nFlags, point);
}

void CMyView::rise() 
{
    center.y -= 5;
    pDC = GetDC();
    br.CreateSolidBrush(color);
    pDC->SelectObject(&br);
    pDC->Ellipse(center.x - r, center.y - r, center.x + r, center.y + r);
    br.DeleteObject();
}

void CMyView::OnTimer(UINT nIDEvent) 
{
    // TODO: Add your message handler code here and/or call default
    if (nIDEvent == 1) {
        CDC* pDC = GetDC();
        CRect rect;
        GetClientRect(&rect);
        pDC->FillSolidRect(rect, GetSysColor(COLOR_WINDOW)); // 用背景色覆盖整个视图区域
        for (int i = 0; i < 5; i++) {
            br.CreateSolidBrush(color);
            pDC->SelectObject(&br);
            pDC->Ellipse(center.x - r, center.y - r, center.x + r, center.y + r);
            br.DeleteObject();
        }
        ReleaseDC(pDC);
        center.y -= 5;
    }
}