afabri/surfer2

straight skeleton code implementing Aichholzer and Aurenhammer's Triangulation based algorithm

Surfer2

Surfer2 is an implementation of Aichholzer and Aurenhammer's triangulation based straight skeleton algorithm using CGAL. It has been developed at the University of Salzburg's Computational Geometry and Applications Lab.

Obtaining the source code

Clone the git repository: The logging class is included via a git submodule, so either clone the source using `

git clone --recurse-submodules https://github.com/cgalab/surfer2

or, if you already have a checkout without the submodule, go to the working copy and

git submodule update --init --recursive

If all works well, you should see files both at the top level of your working copy as well as in surf/easyloggingpp.

If you did not clone the source with git, you may have to get easyloggingpp yourself. You can find it at https://github.com/cgalab/easyloggingpp

Build requirements

To build surfer2, you need a c++ toolchain, cmake, and several libraries including CGAL. On Debian 10 (buster), installing the following packages is sufficient to build surfer2:

• build-essential
• cmake
• libboost-graph-dev
• libboost-iostreams-dev
• libcgal-dev
• libcgal-qt5-dev
• libqt5opengl5-dev
• libqt5svg5-dev
• qtbase5-dev
• clang

To also build the test suite, you will additionally need libgtest-dev. If you have an older libgtest-dev (<= 1.7), such as on Ubuntu 18.04, you may need to explicitly install googletest also.

Building

To build surfer, run cmake and make:

mkdir build &&
cd build &&
CXX=clang++ cmake -DCMAKE_BUILD_TYPE=Release .. &&
make

This will create a release build, without expensive assertions. To build the debug build, pass -DCMAKE_BUILD_TYPE=Debug to cmake, or nothing at all. If you prefer gcc to clang, don't set the CXX environment variable when calling cmake.

Other build options are TEST_SUITE, which defaults to off (to enable, pass -DTEST_SUITE=on to cmake), and BUILD_SHARED_LIBS and LIB_ONLY (also off by default).

Running the command line client or gui

Both the command line client, surfer, as well as the gui, surfgui take GraphML files with coordinates as specified in Graph-Attributes as input.

./cc/surfer ../test-data/srpg0000025.graphml

./gui/surfgui ../test-data/srpg0000028.graphml

They accept several options, one of them is --help which prints a list of all options. The --component=<component> option restricts computation to component number <component>, an integer number starting at 0. For polygonal input, l and r are accepted for (left and right). The default is -1, which computes all components' straight skeleton, one after the other. A value of -2 propagates the wavefront in all components at the same time.

To create a .graphml file from a .line or .ipe file use

ord-format <linefile>

from the format-converter repository.

GUI

The gui has a set of buttons near the top. They all have mouse-over tool tips. The block starting with i controls layer visibility:

• i toggles visibility of the input PSLG,
• I toggles visibility of the input PSLG labels,
• w toggles visibility of the wavefront,
• t toggles visibility of the triangulation,
• T toggles visibility of the triangulation labels,
• s toggles visibility of the straight skeleton (once finalized),
• S toggles visibility of the straight skeleton labels (once finalized, and only in the debug build).

All of those options can be controlled with the keyboard using Alt+<letter>. Use Alt+Shift for capitals.

The next two blocks deal with time and even handling. The functionality behind these buttons can also be accessed by simply pressing the corresponding keyboard key.

• , moves the time forward to the time of the next event,
• <backspace> moves the time back to the time of the last event,
• b moves the drawing backwards in time. Elements are not necessarily consistent in the past.
• N moves the time forwards, including event processing.
• M moves the time forwards, not including event processing. As such, the future is not necessarily shown correctly.
• n Moves to the next event time and processes it.
• <enter> Processes all remaining events.

Lastly, there are a few options that modify the drawing only. These sometimes help in debugging or investigating how things looked just prior to an event.

• - decrease drawing offset (draw things at a time earlier than now),
• + increase drawing offset (draw things at a time later than now),
• = reset drawing offset.

License

Surfer is free software. You may redistribute it and/or modify it under the terms of the GNU General Public License (v3).