StackedBoxes.org

From Bare Docs to Bare Metal

Thu, 30 Dec 2021 00:00:00 +0000

Many tutorials show how to do bare metal programming on a Raspberry Pi. Some are very good, but they tend to have a certain magic vibe on them. “Trust me, just use the following magic constants and it will work”. I can’t help but ask, hey, where did this magic come from? What if I wanted to figure out all details by myself?

El Calafate and Ushuaia

Fri, 10 Apr 2020 00:00:00 +0000

Here are some quick notes about a 10-day trip in February 2020 to El Calafate and Ushuaia, two truly wonderful destinations in southern Argentina 🇦🇷.

Polar Method

Tue, 17 Mar 2020 00:00:00 +0000

We definitely don’t have a shortage of methods for generating normally-distributed random numbers from a source of uniformly-distributed random numbers. One of such methods is the so called Polar Method, a variation of the Box-Muller Transform, which I already described before. You might want to take a look at it before reading this.

Box-Muller Transform

Tue, 28 Jan 2020 00:00:00 +0000

This algorithm is named after George Edward Pelham Box and Mervin Edgar Muller, who published it on a two-page paper in 1958. The idea was not original, though: it appeared already in the 1934 book Fourier Transforms in the Complex Domain, by Raymond E. A. C. Paley and Norbert Wiener. Stigler’s law strikes again!

Euclidean Algorithm

Sun, 05 Jan 2020 14:30:30 +0000

We don’t know for sure when the Euclidean Algorithm was created nor by whom, but it was made famous around 300 BC by the Elements – the magnum opus of Greek mathematician Euclid. Wikipedia describes it as “one of the oldest algorithms in common use” and Knuth affectionately calls it “the granddaddy of all algorithms”.

DUMP

Sun, 05 Jan 2020 14:30:00 +0000

This is a repository of more or less random programming things, made for my own amusement and edification. I don’t know how this will evolve over time (if at all), but I envision this as a collection of interactive visual explanations of algorithms and data structures.

Noeis pelo Mundo

Tue, 24 Dec 2019 00:00:00 +0000

🎄 Feliz Natal! 🎅

(In Portuguese 😉)

Windows Killed My GRUB: What Now?

Thu, 20 Dec 2018 00:00:00 +0000

So it happened again. After some random event like a system upgrade or power failure(?), what I see upon booting, somehow, is Windows Boot Manager instead of GRUB. Here’s how I fixed it.

Using an Xbox 360 Controller with OpenMSX

Sun, 20 May 2018 00:00:00 +0000

Just sharing the OpenMSX settings I am using in order to properly use an Xbox 360 controller. The mappings are optimized for Konami games (in particular, Metal Gear 2: Solid Snake).

Trying out GDNative

Sun, 20 Aug 2017 00:00:00 +0000

I’ve been watching and toying a little bit with the Godot game engine for some time now, and it impressed me in several ways. One thing I missed, however, was a satisfying way to write more efficient code in those ever rarer situations in which GDScript¹ couldn’t give the speed I wanted. I could write a module in C++, but this involved recompiling the whole engine and, well, programming in C++.

Now, with the upcoming Godot 3.0 (currently in alpha), a much nicer alternative has been introduced: GDNative. I tested it and it mostly worked. Here’s a summary of my experience.

A Conceptual Machine Learning Primer, Part 2

Sat, 01 Jul 2017 00:00:00 +0000

On the second and final part of this conceptual introduction to Machine Learning (ML), I’ll discuss its relationship with other areas (like Data Science) and describe what I perceive as a common theme among many of the ML algorithms. Emphasis on “what I perceive”: don’t take this as the truth.

A Conceptual Machine Learning Primer, Part 1

Tue, 20 Jun 2017 00:00:00 +0000

“Machine Learning” is not just a buzzword — arguably, it is two. Almost everybody seems to be using Machine Learning (ML) in a way or another, and those who aren’t are looking forward to use it. Sounds like a good topic to know about. I did some nice Neural Network stuff with some colleagues in school in the late 90s¹. Maybe I could just brag that I have nearly 20 years of experience in the field, but this would not be exactly an honest statement, as I didn’t do much ML since then.

Anyway, this is a fun, useful and increasingly important field, so, I guess it is time to do some ML for real. Here’s the first set of notes about my studies, in which I present some important concepts without getting into specific algorithms.

Acklam's Algorithm for the Inverse Normal CDF

Mon, 01 May 2017 00:00:00 +0000

Once upon a time, Peter John Acklam devised a nice algorithm to approximate the quantile function (AKA inverse cumulative distribution function, or inverse CDF) of the normal distribution. He made the algorithm freely available, but unfortunately his page describing it has been timing out for quite a while. So, for reference, here’s a quick overview of his algorithm.

The homepage is dead!

Sat, 25 Mar 2017 00:00:00 +0000

I don’t remember when I created my first homepage, but I know that in 1998 I already had one. It had a mix of content created by myself and those funny things people shared by email back then. I soon dumped all “third-party” content and made my homepage a repository of stuff I created.

LMB's Quotes

Sat, 08 Dec 2012 00:00:00 +0000

This was the philosophical and narcissistic section of my homepage, now converted into a blog post. It has some drops of wisdom uttered by me during the years (from around 1998 until 2012).

Frases de Candidatos

Sat, 01 Dec 2012 00:00:00 +0000

Para o deleite de todos, aqui vai minha coleção pessoal de pérolas recolhidas durante campanhas políticas.

Open Scene Graph: More State — Lights, Textures and Shaders

Thu, 27 Jan 2011 00:00:00 +0000

I could made this part fit into a single paragraph. Serious, just watch:

Light, textures and shaders are part of the rendering state, so they are handled just as shown in the previous post. Sure, using them requires the use of subclasses of osg::StateAttribute that have not been shown, like osg::Light, osg::Texture2D, and osg::Program, but the idea is the same. So, just spend some time with the Open Scene Graph reference documentation and you are done.

Paixão Nacional

Tue, 15 Jun 2010 00:00:00 +0000

“Muito boa noite, amigos! Falamos ao vivo diretamente da Serra Fluminense para a transmissão de uma emocionante e decisiva partida entre Brasil e União Soviética. Este embate é esperado com grande expectativa pela torcida, e não tenho dúvida de que temos grandes emoções pela frente. Junto comigo para esta transmissão, ao meu lado aqui na cabine, Joélson Seicheles. Boa noite, Joélson! O que a torcida brasileira pode esperar do jogo de hoje?”

Open Scene Graph: Completing the Triad: StateSets

Wed, 05 May 2010 00:00:02 +0000

In the previous part, we talked about two very important OSG concepts: nodes and drawables. Now, we’ll deal with a third very important concept: state sets. These form what I consider the triad of the very fundamental OSG concepts.

Open Scene Graph: The Basics

Wed, 05 May 2010 00:00:01 +0000

Having conceived this text as a practical guide, I was tempted to jump right into action, with an exciting example program displaying some nifty 3D graphics. But, also having conceived this text as something useful for “very beginners”, I resisted this temptation and decided to start with some basic concepts without which the Open Scene Graph (OSG) would not make sense. So, before talking about OSG per se, I’ll start spending a little time with a quite fundamental question.

A Short Introduction to the Basic Principles of the Open Scene Graph

Wed, 05 May 2010 00:00:00 +0000

This is the prologue for a series of posts teaching the most important concepts for anyone learning to use the Open Scene Graph (OSG).

Puzzles

Wed, 21 Apr 2010 00:00:00 +0000

Print this page and enjoy hours of hinteligent entertainment. Guaranteed fun for all ages!

Diversão com Software Livre

Sun, 27 Sep 2009 00:00:00 +0000

Apresentação feita por mim no “Dia da Liberdade de Software” (Feevale, Novo Hamburgo, RS), em setembro de 02009 e reprisada no TcheLinux 2009 (PUC-RS, Porto Alegre, RS).

Lua: Uma linguagem de extensão extensível

Thu, 30 Apr 2009 00:00:00 +0000

Esse foi um minicurso que eu ministrei na Game Development School (GDS) da Unisinos, em novembro de 02007. Estão disponíveis os slides e o código fonte usado nos exemplos.

The World's Most Dangerous Professions

Thu, 30 Apr 2009 00:00:00 +0000

Barack Obama is the 44^th president of the USA. In the history of that country, four presidents have been murdered. This means that almost 9.1% of the USA presidents have been killed during their terms. Another 11 presidents died of natural causes during their terms. This sums up to an impressive number: more than 1/3 of the presidents of the USA died while presidents of the USA. Therefore, one can easily conclude that president of the USA is one of the most dangerous jobs of the world!

Close Encounters

Thu, 01 Feb 2007 00:00:00 +0000

This the first cartoon on my page created 100% digitally. That’s Inkscape helping those who can’t draw well!

Cadeiras caras no TRE de São Paulo

Sat, 22 Jul 2006 00:00:00 +0000

O Jornal da Band de ontem denunciou que, no TRE de São Paulo, “os magistrados compraram cadeiras que custam 12.796 reais [mais de três anos do salário mínimo da época, que era de R$350,00] cada uma”. A repórter foi até o TRE, mas só foi atendida na rua, pelo interfone. Podiam pelo menos ter convidado a coitada para entrar e sentar.

Lua e XML

Wed, 19 Jul 2006 00:00:00 +0000

Eu sou daqueles que ainda não conseguiram entender o que existe de tão espetacular no tal XML. Até admito que ele possa ser bom para algumas aplicações, e talvez até possa ser a melhor opção para um ou outro caso, mas o fato é que se faz barulho demais sobre isso. Diz-se que “este programa usa arquivos XML” como se isso fosse um recurso do programa, uma vantagem para o usuário. Entretanto, o que me parece é que, na maioria dos casos, algum outro formato mais simples, legível e “escrevível” resolveria o problema com bem mais facilidade e eficiência.

Poçostergação

Wed, 21 Jun 2006 00:00:00 +0000

Amanheça com alongamento:\ estique bem o pescoço,\ e pule no poço noutro momento.

Carros roubados escondidos em estacionamento

Wed, 07 Jun 2006 00:00:00 +0000

Notícia no Jornal de RBS: “Ladrões usam estacionamento para esconder carros roubados.” Mas é claro! Se deixar na rua, periga alguém roubar!

The Terrifying Olympic Escape

Sun, 28 May 2006 00:00:00 +0000

This was my first (and one of the only) Flash animations I created, in the year 02002. Turn the volume up!

Despertar

Thu, 16 Mar 2006 00:00:00 +0000

O despertador estava acertado para tocar às seis e meia. Nem precisava. Minutos antes disso, por si mesma, abriu os olhos. E despertou com uma questão insólita ocupando sua atordoada mente. O que é melhor: uma certeza medíocre ou uma dívida otimista?

The Illustrated Guide to Bootloaders

Tue, 21 Feb 2006 00:00:00 +0000

Trying to decide whether you should install GRUB or LILO? Afraid of making the wrong decision? The Illustrated Guide to Bootloaders comes to your rescue!

The Invention of the Normal Distribution

Tue, 19 Apr 2005 00:00:00 +0000

Update, 2016-03-19: A real scan of the cartoon, instead of the previous, horrendous photograph.

Undergrad Class Assignments

Tue, 24 Aug 2004 00:00:00 +0000

Undergrad Class Assignments

These are some class assignments I did when I was an undergraduate Computer Science student. If nobody find them useful, they’ll at least help me to remember some of the assignments I enjoyed most.

The majority of the stuff here (specially the older ones) are in Portuguese.

All the software available here is licensed under the Cursing License (which I haven’t written yet — but I will write it someday).

Teste Psicológico

Mon, 30 Jun 2003 00:00:00 +0000

Este é o meu famoso teste psicológico, em versão on-line. E, para aqueles que não perceberem por si sós: esse teste não é sério!

Know Your Future

Wed, 25 Jun 2003 00:00:00 +0000

Your destiny doesn’t depend solely on the stars and on the numbers. Your credit card is decisive, too. So, here it is, with exclusivity, the most powerful fortune telling system based on your credit card number.

Retaliações

Sun, 14 Apr 2002 00:00:00 +0000

A bomba pode derrubar prédios,\ abrir crateras,\ mudar a geografia.

Organização do Exército Romano

Fri, 11 Jan 2002 00:00:00 +0000

Encontrei este no meu caderno de história da oitava série (isso foi lá pelo ano de 01994).

Certain Night in December

Sun, 09 Sep 2001 00:00:00 +0000

Technically, this is in Portuguese, but I guess this won’t matter much.

f’(x)

Thu, 05 Jul 2001 00:00:00 +0000

Tente entender esse! (Se conseguir, é forte indício de que você tem um alto nível de nerdice.)

Os ETs Chegaram

Fri, 15 Jun 2001 00:00:00 +0000

Os ETs chegaram! Aterrissaram seu disco voador no meio do estádio no dia da finalíssima. São amigos. Estão em missão de paz. Vêm do planeta Ho͡pgkųl. Promovem projetos de intercâmbio cultural, turístico e tecnológico pela galáxia.

A Língua Ilustrada

Thu, 17 May 2001 00:00:00 +0000

Uma série de trocadilhos linguístico-visuais.

Final Feliz

Sun, 13 May 2001 00:00:00 +0000

Conversa de dois amigos durante um lanchinho, algum dia no futuro:

Numbers

Fri, 09 Mar 2001 00:00:00 +0000

Do not try to understand this one!

VOX Project

Thu, 15 Oct 1998 00:00:00 +0000

VOX is a speech recognition school project I worked in back in 1998. Here’s a brief description of the project, and most of the artifacts we produced back then.

Os Dois Sapos

Wed, 30 Aug 1995 00:00:00 +0000

Em um banhado moravam dois sapos. Um deles era quieto, nunca falava. O outro era tagarela, vivia falando.

About

Mon, 01 Jan 0001 00:00:00 +0000

My name is Leandro Motta Barros, a Brazilian guy from the city of São Leopoldo in the State of Rio Grande do Sul. I studied Computer Science, I’ve always worked programming computers, but I have interest in a very wide range of topics.

My personal homepage, was initially a repository of the stuff I created. Then I reshaped it as something different, and as I write these words I don’t really know what it will become.