【FastCAE源码阅读9】鼠标框选网格、节点的实现

一、VTK的框选支持类vtkInteractorStyleRubberBandPick

FastCAE的鼠标事件交互类是PropPickerInteractionStyle,它扩展自vtkInteractorStyleRubberBandPick。vtkInteractorStyleRubberBandPick类可以实现鼠标框选物体,默认情况下按下键盘r键开启框选模式,这时拖动鼠标可拾取物体。VTK官网有其例子:HighlightSelection。

二、FastCAE框选产品设计

我们看FastCAE的鼠标拾取产品设计。其只支持框选网格点与网格单元,几何点、线、面都不支持。框选网格单元效果如下:

在VTK的给的案例中,按r键是为了打开vtkInteractorStyleRubberBandPick类的框选开关,设置vtkInteractorStyleRubberBandPick字段CurrentMode=1(VTKISRBP_SELECT),表示开启框选模式。VTK中vtkInteractorStyleRubberBandPick.cxx源码如下:

void vtkInteractorStyleRubberBandPick::OnChar()
{
  switch (this->Interactor->GetKeyCode())
  {
    case 'r':
    case 'R':
      // r toggles the rubber band selection mode for mouse button 1
      if (this->CurrentMode == VTKISRBP_ORIENT)
      {
        this->CurrentMode = VTKISRBP_SELECT;
      }
      else
      {
        this->CurrentMode = VTKISRBP_ORIENT;
      }
      break;
    case 'p':
    case 'P':
    {
      vtkRenderWindowInteractor* rwi = this->Interactor;
      int* eventPos = rwi->GetEventPosition();
      this->FindPokedRenderer(eventPos[0], eventPos[1]);
      this->StartPosition[0] = eventPos[0];
      this->StartPosition[1] = eventPos[1];
      this->EndPosition[0] = eventPos[0];
      this->EndPosition[1] = eventPos[1];
      this->Pick();
      break;
    }
    default:
      this->Superclass::OnChar();
  }
}

而在FastCAE框选时,不需要按下r键,其原因在用切换拾取模式时,直接改掉了CurrentMode的值,源码如下(注意看这个函数最后一行):

void PropPickerInteractionStyle::setSelectModel(int m)
{
	_selectModel = (SelectModel)m;
	this->CurrentMode = 0;
	if (_actor != nullptr)
		_actor->GetProperty()->DeepCopy(_property);
	_actor = nullptr;
	_preGeoSeltctActor = nullptr;
	_selectItems.clear();
	emit grabKeyBoard(false);
	switch (_selectModel)
	{
	case ModuleBase::MeshNode:
	case ModuleBase::MeshCell:
	case ModuleBase::GeometryWinPoint:
	case ModuleBase::GeometryWinCurve:
	case ModuleBase::GeometryWinSurface:
	case ModuleBase::GeometryWinBody:
		emit grabKeyBoard(true);
		break;
	case ModuleBase::GeometryPoint:
	case ModuleBase::GeometryCurve:
	case ModuleBase::GeometrySurface:
	case ModuleBase::GeometryBody:
		break;
	case ModuleBase::BoxMeshNode: // 当选择方式是框选时,直接设置开始框选
	case ModuleBase::BoxMeshCell:
	case ModuleBase::DrawSketch:
		this->CurrentMode = 1;
		break;
	}
}

这种设计的好处是不用按键盘进行交互,但造成激活框选按钮之后,视图的角度无法更改。本来按住左键拖拽可以旋转视图的,打开框选之后就失效了。

其框选还有一个比较严重的问题:框选会同时拾取物体的表面与背面单元,效果如下:

这种效果惊不惊喜,意不意外!?很多场景下,这种拾取是不满足要求的。进一步分析其框选逻辑就很好理解这种现象了。

三、框选计算逻辑

PropPickerInteractionStyle::OnLeftButtonUp()处理鼠标抬起事件,框选计算哪些物体要被选中的逻辑也在这里被触发。

void PropPickerInteractionStyle::OnLeftButtonUp()
{
	vtkInteractorStyleRubberBandPick::OnLeftButtonUp();
	if (_selectModel == None && !_mouseMoved)
		emit this->clearAllHighLight();
	if ((_selectModel != BoxMeshCell) && (_selectModel != BoxMeshNode) && (_selectModel != DrawSketch))
		return;
	if (this->CurrentMode == 0)
		return;
	//		_selectItemIDs->SetNumberOfValues(0);
	_selectItems.clear();
	int *endPos = this->GetInteractor()->GetEventPosition();
	_endPos[0] = endPos[0];
	_endPos[1] = endPos[1];
	//		qDebug() << "end  " << _endPos[0] << "   " << _endPos[1];
	if (_selectModel != DrawSketch)
	{
		vtkActor *ac = nullptr;
		vtkAreaPicker *areaPicker = dynamic_cast<vtkAreaPicker *>(this->GetInteractor()->GetPicker());
		ac = areaPicker->GetActor();
		if (ac == nullptr)
			return;
	}
	switch (_selectModel)
	{
	case ModuleBase::BoxMeshNode: // 计算哪些节点被选中
		boxSelectMeshNode();
		break;
	case ModuleBase::BoxMeshCell: // 计算哪些单元要被选中
		boxSelectMeshCell();
		break;
	case ModuleBase::DrawSketch:
		_coordinate->SetCoordinateSystemToDisplay();
		_coordinate->SetValue(endPos[0], endPos[1], 0);
		double *d = _coordinate->GetComputedWorldValue(_renderer);
		emit mouseReleasePoint(d);
		break;
	}
	_mouseMoved = false;
	_leftButtonDown = false;
}

boxSelectMeshNode()、boxSelectMeshCell()函数分别哪些节点、单元要被拾取。

void PropPickerInteractionStyle::boxSelectMeshNode()
{
	emit clearAllHighLight(); // 清除掉当前高亮
	_selectItems.clear(); // 清理当前选择项
	// Forward events
	int range[4];
	this->getBoxRange(range);  // 获取框选矩形的坐标
	vtkActorCollection *actors = _renderer->GetActors(); // 获取当前的场景中所有actor
	actors->InitTraversal();
	const int nac = actors->GetNumberOfItems();
	for (int i = 0; i < nac; ++i) // 对Actor进行遍历
	{
		vtkActor *actor = actors->GetNextActor();
		if (actor == nullptr)
			if (!actor->GetVisibility())
				continue;
		if (!actor->GetPickable())
			continue;
		vtkMapper *mapper = actor->GetMapper();
		if (mapper == nullptr)
			continue;
		vtkDataSet *dataset = mapper->GetInputAsDataSet();
		if (dataset == nullptr)
			continue;
		vtkDataArray *IDS = dataset->GetPointData()->GetArray("IDS"); // 提取Actor的点数据
		if (IDS == nullptr)
			continue;
		this->selectMesh(dataset, range);
	}
	emit highLight(&_selectItems);
}

void PropPickerInteractionStyle::selectMesh(vtkDataSet *dataSet, int *range)
{
	vtkRenderer *render = this->GetInteractor()->GetRenderWindow()->GetRenderers()->GetFirstRenderer();
	vtkSmartPointer<vtkCoordinate> coordinate = vtkSmartPointer<vtkCoordinate>::New();
	coordinate->SetCoordinateSystemToWorld();
	coordinate->GetComputedDisplayValue(render);

	if (_selectModel == BoxMeshNode)
	{
		vtkDataArray *ids = dataSet->GetPointData()->GetArray("IDS"); // 获取点集
		const int npoint = dataSet->GetNumberOfPoints();
		for (int i = 0; i < npoint; ++i)
		{
			double coor[3];
			dataSet->GetPoint(i, coor); // 获取点的坐标
			coordinate->SetValue(coor); // 将点的坐标设置给coordinate
			int *va = coordinate->GetComputedDisplayValue(render); // 计算屏幕坐标
			if (isPointInRange(va, range)) // 是否在鼠标框内部
			{
				double *k_id = ids->GetTuple2(i); // 看不懂?
				_selectItems.insert(k_id[0], k_id[1]);
			}
		}
	}
	else if (_selectModel == BoxMeshCell)
	{
		vtkDataArray *ids = dataSet->GetCellData()->GetArray("IDS"); // 获取cell数据
		const int ncell = dataSet->GetNumberOfCells();
		for (int i = 0; i < ncell; ++i) // 遍历cell
		{
			vtkCell *cell = dataSet->GetCell(i); // 当前的cell
			double pcenter[3] = {0};
			cell->GetParametricCenter(pcenter); // 获取当前cell的中心点参数坐标
			int subid;
			double coor[3];
			double w[100];
			cell->EvaluateLocation(subid, pcenter, coor, w); // 根据参数坐标获取中心点世界空间坐标
			coordinate->SetValue(coor);
			int *va = coordinate->GetComputedDisplayValue(render); // 计算屏幕坐标
			if (isPointInRange(va, range)) // 屏幕坐标是否在选择框内
			{
				double *k_id = ids->GetTuple2(i);
				_selectItems.insert(k_id[0], k_id[1]);
			}
		}
	}
}

根据以上代码,框选点时,直接根据点坐标计算其投影到屏幕上的坐标,判断是否在选择框内。单元是判断中心点是否在选择框内部。因为投影之后,丢弃了深度方向的信息,没有考虑物体的遮挡信息,所以框选时表面、背面均可选择。而且其计算框选时遍历所有网格,没有借助一些加速结构,如BVH树等,造成框选效率较低,当网格数量较多时,这种方式很慢。

总结:

FastCAE的框选逻辑过于简单,只是demo阶段,实际的CAE软件的拾取逻辑要远比这复杂。

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