| OpenCV 4.3.0 Open Source Computer Vision

Creating Widgets

## Goal

In this tutorial you will learn how to

- Create your own widgets using WidgetAccessor and VTK.
- Show your widget in the visualization window.

## Code

You can download the code from here.

#ifndef USE_VTK
#include <iostream>
int main()
{
std::cout << "This sample requires direct compilation with VTK. Stop" << std::endl;
return 0;
}
#else
#include <opencv2/viz.hpp>
#include <opencv2/viz/widget_accessor.hpp>
#include <iostream>
#include <vtkPoints.h>
#include <vtkTriangle.h>
#include <vtkCellArray.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkIdList.h>
#include <vtkActor.h>
#include <vtkProp.h>
using namespace cv;
using namespace std;
static void help()
{
cout
<< "--------------------------------------------------------------------------" << endl
<< "This program shows how to create a custom widget. You can create your own "
<< "widgets by extending Widget2D/Widget3D, and with the help of WidgetAccessor." << endl
<< "Usage:" << endl
<< "./creating_widgets" << endl
<< endl;
}
class WTriangle : public viz::Widget3D
{
public:
WTriangle(const Point3f &pt1, const Point3f &pt2, const Point3f &pt3, const viz::Color & color = viz::Color::white());
};
WTriangle::WTriangle(const Point3f &pt1, const Point3f &pt2, const Point3f &pt3, const viz::Color & color)
{
// Create a triangle
vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
points->InsertNextPoint(pt1.x, pt1.y, pt1.z);
points->InsertNextPoint(pt2.x, pt2.y, pt2.z);
points->InsertNextPoint(pt3.x, pt3.y, pt3.z);
vtkSmartPointer<vtkTriangle> triangle = vtkSmartPointer<vtkTriangle>::New();
triangle->GetPointIds()->SetId(0,0);
triangle->GetPointIds()->SetId(1,1);
triangle->GetPointIds()->SetId(2,2);
vtkSmartPointer<vtkCellArray> cells = vtkSmartPointer<vtkCellArray>::New();
cells->InsertNextCell(triangle);
// Create a polydata object
vtkSmartPointer<vtkPolyData> polyData = vtkSmartPointer<vtkPolyData>::New();
// Add the geometry and topology to the polydata
polyData->SetPoints(points);
polyData->SetPolys(cells);
// Create mapper and actor
vtkSmartPointer<vtkPolyDataMapper> mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
#if VTK_MAJOR_VERSION <= 5
mapper->SetInput(polyData);
#else
mapper->SetInputData(polyData);
#endif
vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
// Store this actor in the widget in order that visualizer can access it
viz::WidgetAccessor::setProp(*this, actor);
// Set the color of the widget. This has to be called after WidgetAccessor.
setColor(color);
}
int main()
{
help();
viz::Viz3d myWindow("Creating Widgets");
WTriangle tw(Point3f(0.0,0.0,0.0), Point3f(1.0,1.0,1.0), Point3f(0.0,1.0,0.0), viz::Color::red());
myWindow.showWidget("TRIANGLE", tw);
myWindow.spin();
return 0;
}
#endif

## Explanation

Here is the general structure of the program:

- Extend Widget3D class to create a new 3D widget.
  class WTriangle : public viz::Widget3D
  {
  public:
  WTriangle(const Point3f &pt1, const Point3f &pt2, const Point3f &pt3, const viz::Color & color = viz::Color::white());
  };
- Assign a VTK actor to the widget.
  // Store this actor in the widget in order that visualizer can access it
  viz::WidgetAccessor::setProp(*this, actor);
- Set color of the widget.
  // Set the color of the widget. This has to be called after WidgetAccessor.
  setColor(color);
- Construct a triangle widget and display it in the window.
  WTriangle tw(Point3f(0.0,0.0,0.0), Point3f(1.0,1.0,1.0), Point3f(0.0,1.0,0.0), viz::Color::red());
  myWindow.showWidget("TRIANGLE", tw);

## Results

Here is the result of the program.