ForcePAD

The conceptual model of ForcePAD 3

When redesigning an application, there is an opportunity to rethink the existing design and make improvements. In the case of ForcePAD 2, it was a simple pixel-based drawing application with a single layer for drawing. Users could add loads and boundary conditions on top of the drawing, and results were displayed on top of the image layer.

With ForcePAD 3, I aim to introduce a layered model that allows users to add multiple drawing layers on top of each other, similar to how a designer or architect uses sketch paper. These layers can be hidden and made transparent, providing more flexibility when sketching. In the following sections, I will provide a detailed description of the model and the main classes that implement it.

Building for many platforms is hard

Choosing the right libraries for your application is just one step in making it run on multiple operating systems. ForcePAD uses CMake to build the application on multiple platforms. CMake is an excellent tool that generates build files for each platform. On Windows it generates Visual Studio solution files. On other platform it generates make files. I started implementing most of the tooling for ForcePAD on Windows thinking that most of this can be easily transferred to macOS. This what not that easy. I will go through the setup in the following sections.

A new backend for ForcePAD

The current version of ForcePAD is implemented using the FLTK library and OpenGL for graphics. At the time FLTK provided an easy way of implementing an multiplatform application that could run on Windows and Unix/Linux. FLTK provided both an intuitive environment for designing the 2D user interface as well as easy OpenGL context creation. OpenGL context creation on Windows and Unix was implemented very differently on each platform. Having just one way of this enabled ForcePAD to be implemented in a single code base.

Thoughts the ForcePAD application

ForcePAD was developed as part of my PhD thesis almost 20 years ago. The application was developed in C++ using OpenGL for graphics and FLTK for the user interface. At the time, it was state-of-the-art and compiled on all platforms, such as Linux, Windows, and SGI Irix 6.5(!). The application was used extensively in teaching and is still used today.