需求：场景中一个actor，鼠标悬浮时  显示此actor的信息。

效果：

 实现：

1，利用vtkInteractorStyleTrackballCamera 的OnMouseMove 事件 判断是否处于悬浮状态

2，判断悬浮后，首先将世界坐标转为屏幕坐标，然后分别绘制文字和背景，当不处于悬浮时，移除文字和背景。

//世界坐标 转屏幕坐标
            double worldCoord[3] = {iter->second.x, iter->second.y, iter->second.z};
            vtkSmartPointer<vtkCoordinate> pCoorPress = vtkSmartPointer<vtkCoordinate>::New();
            pCoorPress->SetCoordinateSystemToWorld();
            pCoorPress->SetValue(worldCoord);
            int *dispCoord = pCoorPress->GetComputedDisplayValue(Renderer);
            qDebug() << dispCoord[0] << dispCoord[1];
            vtkNew<vtkNamedColors> colors;

            //绘制文字
     QString qstr = QString("x:%1 y:%2 z:%3").arg(iter->second.x).arg(iter->second.y).arg(iter->second.z);
            vtkUnicodeString str = vtkUnicodeString ::from_utf8(qstr.toUtf8().data());
            txtActor->SetInput(str.utf8_str());
            vtkTextProperty* txtprop = txtActor->GetTextProperty();
            txtprop->SetFontFamilyToArial();
            //txtprop->BoldOn();
            txtprop->SetFontSize(36);
            txtprop->ShadowOn();
            //txtprop->SetShadowOffse()

//背景
            //获取文字宽高
            double boundingBox[6];
            txtActor->GetBoundingBox(Renderer, boundingBox);
            double width = (boundingBox[1] - boundingBox[0])+20;
            double height = (boundingBox[3] - boundingBox[2])+20;


            vtkSmartPointer<vtkImageData> backgroundImage =
                    vtkSmartPointer<vtkImageData>::New();
            backgroundImage->SetDimensions(width, height, 1);
            backgroundImage->AllocateScalars(VTK_UNSIGNED_CHAR, 4);

            unsigned char *pixels =
                    static_cast<unsigned char *>(backgroundImage->GetScalarPointer());
            for (int i = 0; i < width * height * 1; ++i)
            {
                pixels[4 * i] = 172;                // 红色分量
                pixels[4 * i + 1] =0;              // 绿色分量
                pixels[4 * i + 2] = 0;              // 蓝色分量
                pixels[4 * i + 3] =  255;
            }
 vtkSmartPointer<vtkImageMapper> backgroundMapper =vtkSmartPointer<vtkImageMapper>::New();
            backgroundMapper->SetInputData(backgroundImage);
            backgroundActor->SetMapper(backgroundMapper);
            backgroundActor->SetDisplayPosition(dispCoord[0]+_pointSize*4, dispCoord[1]-5);
            Renderer->AddActor(backgroundActor);
            ui->viewerWidget->update();