# pvigier's blog

computer science, programming and other ideas

## Commit graph drawing algorithms

This article is one chapter of my master thesis entitled “Design and implementation of a graphical user interface for git”. It describes the algorithm I designed to draw the commit graph in my own prototype git client called gitamine. I have adapted the content so that it fits better with this blog.

Drawing graphs is a very complex topic in general but here we want to draw a specific type of graphs: commit graphs. Commit graphs have several several pieces of information that simplify the problem. The most important ones are that the graph is directed and acyclic and that the commits have timestamps.

Moreover, among the many ways we can draw a directed acyclic graph some are more appropriate for commit graphs. Indeed, programmers manipulate the branches of the graph thus it will be more convenient for them if the representation allows to visualize them easily.

We will first study the different types of graph drawing algorithms used in other clients. Then, we will describe how to place the nodes so that the commit graph is nicely drawable. Finally, we will cover some optimizations done in gitamine to draw and browse the graph in real time.

Tags: graph git

As some of you noticed, Simulopolis is not active since last November. I had still many ideas and many things to do before the game was finished. I started to work on the version 0.0.4 and even had some small features ready.

However, the internship and the master thesis (see next article) for more info) I was doing since September were not going well. Thus, I had to completely stop working on Simulopolis on my free time and work on my master thesis instead to have a little chance to see my thesis accepted by the jury. It was exhausting but eventually I succeeded!

My oral defense was in April so I did not work on Simulopolis for five months. Then, I had to take decisions concerning my future. I chose to leave Paris and to join my girlfriend in a smaller city in the center of France. Moreover, I decided that I did not want to work in a big company. Indeed, I am still young and relatively free from any constraint so I think it is the right moment in order to take my chance as an indie developer.

The bad news is, as you have guessed with the title, that I am not going to resume the development of Simulopolis. But the good news is that I have already started to work on a new project. It is called Vagabond (the name can still change). I will try to blog as much as possible about it so stay tuned! :)

Tags: simulopolis

## Fortune's algorithm, the details

The last few weeks, I worked on an implementation of the Fortune’s algorithm in C++. This algorithm takes a set of 2D points and construct the Voronoi diagram of these points. If you wonder what is a Voronoi diagram, it looks like this:

For each input point, which is called a site, we want to find the set of points which are nearer to this site than to any other site. These sets of points form cells as you can see on the image above.

What is remarkable about the Fortune’s algorithm is that it constructs such diagrams in $O(n\log n)$ time (which is optimal for an algorithm which uses comparisons) where $n$ is the number of sites.

I am writing this article because I find it very hard to implement this algorithm. Until now, it is surely the hardest algorithm I have ever implemented. Thus, I want to share with you the issues I faced and how I solved them.

The code is, as usual, available on github and you will find all the references I used at the bottom of this article.

Tags: cpp geometry

## Simulopolis alpha 3 is released

Today, I release the third alpha version of Simulopolis.

In this post, I will detail a bit what’s new since the initial release.

On this screenshot, you can saw some minor changes on the interface and the main new feature: the newspaper.

Tags: simulopolis

## 3D Perlin noise with numpy

Few weeks ago, a professor from the university of Waterloo contacted me to ask if it was possible to adapt my code for 2D Perlin noise to 3D Perlin noise.

I was very happy that someone was interested by this piece of code. After some thoughts, I answer him that it was possible and I decided to do it.

I move the old code which generates 2D Perlin noise in the file perlin2d.py and I place the code described below for 3D Perlin noise in the file perlin3d.py. You can find all the code in this github repo.