Is it possible to draw 3d segments with CGAL? - c++

Question

I want to draw 3d segments, and the camera can rotate, so that I can observe the segments from various perspectives. I wonder if there is a way to draw them with CGAL? I know that CGAL is not specific for visualization, so the question itself may be some kind of silly. But it will be really helpful for me if it has this function, because I have some experience with CGAL. I have tried to learn OpenGL, but it's not possible for me to master it in a short time. And I don't want to spend much time to learn OpenGL, because I will not use it again in future work.
If CGAL doesn't have this function, could you please recommend some lightweight open source libraries which can draw 3d segments? I don't need a very feature-rich, but huge library. One easy to use and lightweight is best for me. Thanks a lot!

Answer 1

CGAL::Basic_viewer_qt allows to draw points, segments and faces in 2D/3D.
You can define your own viewer inheriting from this class.
As suggested by Marc, have a look at the different draw_XXX.h files to see how this is achieved for several viewers in CGAL.

Answer 2

Following Marc Glisse's and gdamiand's advice, I imitated the class SimpleTriangulation3ViewerQt in file draw_triangulation3.h and wrote a class named SimpleSegments3ViewerQt. It does work. Thanks for your advice! Here is the code.
#pragma once
#include<CGAL/Qt/Basic_viewer_qt.h>
//a struct that describes 3d segment, Point is the data structure of vertex of segment.
template<typename Point>
struct mySegment3d {
Point begin;
Point end;
mySegment3d() {}
mySegment3d(Point b,Point e):begin(b),end(e){}
};
#ifdef CGAL_USE_BASIC_VIEWER
#include<CGAL/Qt/init_ogl_context.h>
//viewer for mySegment3d
//Segs3 is an array of mySegment3d which can be traveled by iterator, such as std::veector<mySegment3d>.
template<class Segs3,class point>
class SimpleSegments3ViewerQt :public CGAL::Basic_viewer_qt
{
typedef Basic_viewer_qt Base;
typedef mySegment3d<point> mySegment3d;
public:
//construct the viewer
SimpleSegments3ViewerQt(QWidget* parent,
const Segs3& seg3,
const char* title = "Basic Segs3 Viewer") :
//First draw: vertices, edges, faces, multi-color, no inverse normal
Base(parent, title, true, true, false, false, true),
s3(seg3)
{
compute_elements();
}
protected:
const Segs3& s3;
protected:
void compute_edge(const mySegment3d& seg) {
add_segment(seg.begin, seg.end, CGAL::IO::blue());
}
void compute_vertex(const mySegment3d& seg) {
add_point(seg.begin, CGAL::IO::red());
add_point(seg.end,CGAL::IO::red());
}
void compute_elements() {
clear();
for (auto itor = s3.begin(); itor != s3.end(); ++itor) {
compute_vertex(*itor);
compute_edge(*itor);
}
}
virtual void keyPressEvent(QKeyEvent* e) {
Base::keyPressEvent(e);
}
};
//draw function
template<typename Segs3,typename Point>
void draw(const Segs3& s3, const char* title = "Segs3 Basic Viewer") {
#if defined(CGAL_TEST_SUITE)
bool cgal_test_suite = true;
#else
bool cgal_test_suite = qEnvironmentVariableIsSet("CGAL_TEST_SUITE");
#endif
if (!cgal_test_suite) {
CGAL::Qt::init_ogl_context(4, 3);
int argc = 1;
const char* argv[2] = { "segs3_viewer","\0" };
QApplication app(argc, const_cast<char**>(argv));
SimpleSegments3ViewerQt<Segs3,Point> mainwindow(app.activeWindow(),
s3, title);
mainwindow.show();
app.exec();
}
}
#endif
Here is an example of usage.
#include<vector>
#include<CGAL/Simple_cartesian.h>
#include"draw_segments_3.h"
typedef CGAL::Simple_cartesian<double> kernel;
typedef kernel::Point_3 Point_3;
//draw_segments3 test
int main() {
std::vector<mySegment3d<Point_3>> segs;
Point_3 p0(0, 0, 0), p1(1, 2, 3), p2(5, 3, 1), p3(3, 1, 10);
mySegment3d<Point_3> s0(p0, p1), s1(p0, p2), s2(p0, p3);
segs.emplace_back(s0);
segs.emplace_back(s1);
segs.emplace_back(s2);
draw<std::vector<mySegment3d<Point_3>>,Point_3>(segs);
}