sdc.CreateCompatibleDC(NULL);
bm.CreateCompatibleBitmap(&sdc,width,height);
sdc.SelectObject(&bm);
sdc.FillSolidRect(0,0,width,height,RGB(0,255,255));
pNewPen2.CreatePen(PS_SOLID ,2, RGB(255,0,0));
sdc.SelectObject(pNewPen2);
sdc.MoveTo(100,100);
sdc.LineTo(100,300);
dc.BitBlt(0,0,width,height,&sdc,0,0,SRCCOPY);
创建画布后画出的线不能显示颜色