看到有人问体绘制切割，正好早上起的比较早，写一个体绘制切割的demo。

VTK：利用qt实现体绘制剪裁

做体绘制渲染一定少不了交互剪裁的功能。一般有两种方式：

搞一个包围盒，移动包围盒实现体渲染的剪裁
像小蚂蚁一样可以在屏幕画任意多边形实现剪裁

结果跟狗啃的一样主要是因为数据尺寸比较小（像素40* 40 * 40），直接抹黑像素肯定很烂

原文

VTK：利用qt实现体绘制剪裁

1 项目地址

在官方案例基础上改的

包围盒案例 https://kitware.github.io/vtk-examples/site/Cxx/Widgets/BoxWidget2/
体渲染案例 https://kitware.github.io/vtk-examples/site/Cxx/VolumeRendering/RayCastIsosurface/
修改后工程 https://github.com/BeyondXinXin/study_vtk

2 包围盒

这个功能vtk直接自带，vtkBoxWidget2可以实现包围盒交互，vtkVolume_XXX_Mapper可以直接输入planes实现剪裁。

/*** @brief The CBvtkBoxWidget3DCallback class* vtkBoxWidget2D 的观察者，响应 InteractionEvent 事件，设置当前的Planes到vtkVolume的Planes。*/
class CBvtkBoxWidget3DCallback final : public vtkCommand {public:static CBvtkBoxWidget3DCallback *New();vtkTypeMacro(CBvtkBoxWidget3DCallback, vtkCommand);CBvtkBoxWidget3DCallback() : transform_(vtkSmartPointer<vtkTransform>::New()) {}~CBvtkBoxWidget3DCallback() = default;vtkVolume *GetVolume() const;void SetVolume(vtkVolume *t_volume);void Execute(vtkObject *caller, unsigned long eventId, void *callData) override;private:vtkVolume *volume_ = {};vtkNew<vtkPlanes> planes_ {};vtkSmartPointer<vtkTransform> transform_ {};
};void CBvtkBoxWidget3DCallback::Execute(vtkObject *caller, unsigned long, void *) {auto *const boxWidget =vtkBoxWidget2::SafeDownCast(caller);auto *const  boxRepresentation =vtkBoxRepresentation::SafeDownCast(boxWidget->GetRepresentation());boxRepresentation->SetInsideOut(1);boxRepresentation->GetPlanes(planes_);volume_->GetMapper()->SetClippingPlanes(planes_);
}class CBvtkBoxWidget3D : public vtkBoxWidget2 {public:static CBvtkBoxWidget3D *New();vtkTypeMacro(CBvtkBoxWidget3D, vtkBoxWidget2);CBvtkBoxWidget3D();~CBvtkBoxWidget3D();
};CBvtkBoxWidget3D::CBvtkBoxWidget3D() {CreateDefaultRepresentation();GetRepresentation()->SetPlaceFactor(1);
}

3 任意多边形

这个基本都是抄的小蚂蚁的交互，屏幕用手术刀画一个任意多边形让后选择剪裁内部还是外部。实现分解：

关闭vtk默认交互
增加屏幕画多边形的交互
切割模型（抹黑图片）
更新数据，开启vtk交互

记得要自己重新实现模型透明度调节（能设置的下限要高于抹黑值），否则抹黑的地方调节透明度时候就露出来了。

3.1 关闭vtk默认交互

使用自定义的Interactor，支持关闭交互

void InteractorStyle::OnMouseMove()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnMouseMove();}
}void InteractorStyle::OnLeftButtonDown()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnLeftButtonDown();}
}void InteractorStyle::OnLeftButtonUp()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnLeftButtonUp();}
}void InteractorStyle::OnMiddleButtonDown()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnMiddleButtonDown();}
}void InteractorStyle::OnMiddleButtonUp()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnMiddleButtonUp();}
}void InteractorStyle::OnRightButtonDown()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnRightButtonDown();}
}void InteractorStyle::OnRightButtonUp()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnRightButtonUp();}
}void InteractorStyle::OnMouseWheelForward()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnMouseWheelForward();}
}void InteractorStyle::OnMouseWheelBackward()
{if (interactive_) {vtkInteractorStyleTrackballCamera::OnMouseWheelBackward();}
}

3.2 增加屏幕画多边形的交互

直接用Qt的自绘控件即可

注意：强烈建议请使用paintGL而不是paintEvent！！！
窗口不能渲染vtk的二维场景。

void RenderWidget::paintGL()
{QVTKOpenGLNativeWidget::paintGL();if (state_ == DrawCutLine && !cutting_points_.isEmpty()) {QPainter painter(this);DrawArea(cutting_points_, painter);}
}void RenderWidget::mousePressEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton && state_ == DrawCutLine) {leftbtn_drag_ = true;cutting_points_.clear();}QVTKOpenGLNativeWidget::mousePressEvent(event);
}void RenderWidget::mouseReleaseEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton && state_ == DrawCutLine) {leftbtn_drag_ = false;}QVTKOpenGLNativeWidget::mouseReleaseEvent(event);
}void RenderWidget::DrawArea(QList<QPointF> &pf, QPainter &painter)
{if (pf.length() < 1) {return;}QPainterPath path(pf[0]);for (int i = 1; i < pf.size(); ++i) {path.lineTo(pf[i]);}QPen pen;pen.setColor(Qt::green);painter.setPen(pen);painter.setBrush(QBrush(Qt::green, Qt::Dense4Pattern));painter.drawPath(path);painter.drawLine(pf[0], pf.last());
}

3.3 切割模型

很多办法都可以，最简单的就是直接遍历图片，利用vtkCoordinate投影到屏幕直接判断是否在QPolygonF里即可

void CutingImagedata(vtkSmartPointer<vtkImageData> image_data,vtkSmartPointer<vtkVolume> volume,vtkSmartPointer<vtkRenderer> renderer,const QPolygonF &polygon, const int &type)
{int img_dims[3];double img_spacing[3];double img_origian[3];image_data->GetDimensions(img_dims);image_data->GetSpacing(img_spacing);image_data->GetOrigin(img_origian);vtkNew<vtkCoordinate> corrdinate;corrdinate->SetCoordinateSystemToWorld();// 不用vtkImageIterator，迭代器没办法获得空间位置// 只是个demo，直接认为vtkImageData 数据是 unsigned char 保存的。如果是其他记得要改。// 只是个demo，直接认为bround是从0，0，0开始的，实际工程记得校验。for (int k = 0; k < img_dims[2]; ++k) {for (int i = 0; i < img_dims[0]; ++i) {for (int j = 0; j < img_dims[1]; ++j) {if (i < 100 && j < 100) {double word_pos[3];word_pos[0] = i * img_spacing[0] + img_origian[0];word_pos[1] = j * img_spacing[1] + img_origian[1];word_pos[2] = k * img_spacing[2] + img_origian[2];corrdinate->SetValue(word_pos);double *display_pos = corrdinate->GetComputedDoubleDisplayValue(renderer);QPointF q_display_pos(display_pos[0], display_pos[1]);if (type == RenderWidget::CutLineInside&& polygon.containsPoint(q_display_pos, Qt::OddEvenFill)) {auto pPixel = static_cast<unsigned char *>(image_data->GetScalarPointer(i, j, k));*pPixel = 0;} else if (type == RenderWidget::CutLineOutside&& !polygon.containsPoint(q_display_pos.toPoint(), Qt::OddEvenFill)) {auto pPixel = static_cast<unsigned char *>(image_data->GetScalarPointer(i, j, k));*pPixel = 0;}}}}}volume->Update();renderer->RemoveVolume(volume);renderer->AddVolume(volume);
}

3.4 更新数据，开启vtk交互

修改图像数据需要更新下vtkVolume和renderWindow。如果要撤回和复位功能，则需要多存几个vtkImageData替换输入。
实际项目使用，一般是每次切割的文件保存到本地“.vti”，方便复位和后续步骤计算。

volume->Update();
renderWindow()->Render();

3.5 直接从官方案例拿的窗口渲染


int main(int argc, char *argv[])
{QApplication a(argc, argv);// vtk 搭建一个体渲染的RenderervtkNew<vtkMetaImageReader> reader;const static QString path = "./etc/HeadMRVolume.mhd";reader->SetFileName(path.toLocal8Bit().data());reader->Update();auto image_data = vtkSmartPointer<vtkImageData>::New();image_data = reader->GetOutput();auto mapper = vtkSmartPointer<vtkOpenGLGPUVolumeRayCastMapper>::New();mapper->SetInputData(image_data);mapper->AutoAdjustSampleDistancesOff();mapper->SetSampleDistance(0.5);mapper->SetBlendModeToIsoSurface();mapper->SetCropping(1);mapper->SetCroppingRegionPlanes(50, 150, 50, 200, 50, 150);mapper->SetCroppingRegionFlags(VTK_CROP_SUBVOLUME);vtkNew<vtkColorTransferFunction> color_transfer_fun;color_transfer_fun->RemoveAllPoints();vtkNew<vtkNamedColors> colors;const auto flesh_color = colors->GetColor3d("flesh").GetData();const double iso1 = 40.0;color_transfer_fun->AddRGBPoint(iso1, flesh_color[0], flesh_color[1], flesh_color[2]);vtkNew<vtkPiecewiseFunction> scalarOpacity;scalarOpacity->AddPoint(iso1, 0.6);vtkNew<vtkVolumeProperty> volume_property;volume_property->ShadeOn();volume_property->SetInterpolationTypeToLinear();volume_property->SetColor(color_transfer_fun);volume_property->SetScalarOpacity(scalarOpacity);auto volume = vtkSmartPointer<vtkVolume>::New();volume->SetMapper(mapper);volume->SetProperty(volume_property);auto renderer = vtkSmartPointer<vtkRenderer>::New();renderer->AddVolume(volume);renderer->SetBackground(colors->GetColor3d("cornflower").GetData());renderer->ResetCamera();volume_property->GetIsoSurfaceValues()->SetValue(0, iso1);renderer->ResetCameraClippingRange();// 显示 WigetRenderWidget *wid = new RenderWidget();wid->setFixedSize(800, 600);wid->renderWindow()->AddRenderer(renderer);QObject::connect(wid, &RenderWidget::SgnCuttingLine, wid, [wid, renderer, image_data, volume](const int &type) {CutingImagedata(image_data, volume, renderer, wid->GetCuttingPolygon(), type);});// 几个按钮以及逻辑GenerateTestButton(wid);// 显示wid->show();return a.exec();
}

3.6 简单的按钮逻辑

void GenerateTestButton(RenderWidget *wid)
{QPushButton *btn_cut = new QPushButton(wid);btn_cut->move(20, 20);btn_cut->setFixedSize(60, 30);btn_cut->setText("cut");QPushButton *btn_cancel = new QPushButton(wid);btn_cancel->move(20, 20);btn_cancel->setFixedSize(60, 30);btn_cancel->setText("cancel");QPushButton *btn_inside = new QPushButton(wid);btn_inside->move(20, 70);btn_inside->setFixedSize(60, 30);btn_inside->setText("inside");QPushButton *btn_outside = new QPushButton(wid);btn_outside->move(20, 120);btn_outside->setFixedSize(60, 30);btn_outside->setText("outside");btn_cut->setVisible(true);btn_cancel->setVisible(false);btn_inside->setVisible(false);btn_outside->setVisible(false);static auto FunChangeBtnState = [btn_cut, btn_cancel, btn_inside, btn_outside](const bool &show) {btn_cut->setVisible(!show);btn_cancel->setVisible(show);btn_inside->setVisible(show);btn_outside->setVisible(show);};QObject::connect(btn_cut, &QPushButton::clicked, wid, [&, wid] {wid->SetStyleState(RenderWidget::DrawCutLine);FunChangeBtnState(true);});QObject::connect(btn_cancel, &QPushButton::clicked, wid, [&, wid] {wid->SetStyleState(RenderWidget::Normal);FunChangeBtnState(false);});QObject::connect(btn_inside, &QPushButton::clicked, wid, [&, wid] {wid->SetStyleState(RenderWidget::CutLineInside);FunChangeBtnState(false);});QObject::connect(btn_outside, &QPushButton::clicked, wid, [&, wid] {wid->SetStyleState(RenderWidget::CutLineOutside);FunChangeBtnState(false);});
}void RenderWidget::SetStyleState(const State &state)
{switch (state) {case DrawCutLine: {style_->interactive_ = false;state_ = DrawCutLine;} break;case CutLineInside:case CutLineOutside: {style_->interactive_ = true;state_ = Normal;emit SgnCuttingLine(state);renderWindow()->Render();} break;case Normal: {style_->interactive_ = true;state_ = Normal;} break;}cutting_points_.clear();
}