how to drag the render window by mouse?

[pyhmail]

I want to Drag my render window by mouse,I use the reposition(int,int) function in RenderWindow class ,but when I drag the render window by mouse ,the render window will flash,how to eliminate the flash phenomenon? my code is follwing:(platform:OGRE + CEGUI)

if(mbWndMove)
{

UIEditor* pEditor = (UIEditor*)FindWindowById(ID_UIEDITOR);
wxPoint oldPos = this->GetPosition();
int offsetX = pos.x - mPrevPos.x;
int offsetY = pos.y - mPrevPos.y;
wxPoint newPos(oldPos.x + offsetX,oldPos.y + offsetY);
Ogre::RenderWindow* pRenderWnd = pEditor->GetRenderWnd();
pRenderWnd->reposition(oldPos.x + offsetX,oldPos.y + offsetY);
mPrevPos = pos;

}