Dec 28

JPEG Support For Libcairo

cairo-bannerLibcairo supports several output file formats (PNG, PDF, SVG) and PNG as input format. But often it is necessary to read and write JPG files as well.

Libjpeg-turbo does all the JPEG stuff. All you have to do is to combine this with the Cairographics library. I implemented two functions in this small C source file. Most of the code is derived by the online code example of libjpeg and I modified it to fit into the Cairographics world.

Look at the comments in the source code for further information and have phun using it. Don’t hesitate to contact me!

-> Download source from Github <-

  • 2016/01/01: Code updated.
  • 2015/12/29: Code updated.

Dec 16

Cypherpunk.at On Hidden Service

Cypherpunk.at is now available on a Tor hidden service at http://7pd3i34noxnxolha.onion/.

Please be aware that this is experimental because it requires a lot of URL rewriting which is done by Apache’s mod_proxy, mod_proxy_http, and mod_proxy_html. I debugged it with Firebug and tried to fix all internal links. Please note that external links to other pages are not rewritten.

The main purpose is to be able to access cypherpunk.at completely surveillance-free (and for me to gain experience in proxying WordPress and mod_proxy_html 😉 )

Dec 15

Evading Firewalls With OnionCat

Evading Firewalls With OnionCat

Dec 13

The Administrator’s TLS Certificate Hell

640_data-webNowadays, a responsible administrator should never run any service without TLS anymore. Unfortunately, this makes life even more difficult for several reasons. This article discusses some problems associated to certificates, specifically in respect to web applications which interactively connect to secondary services.

On one hand TLS configuration requires a lot of knowledge to create a secure configuration. Pages such as Bettercrypto.org give a good support. Continue reading

Dec 11

Calculating Control Points For Bsplines

bspline_0This article explains how to calculate the control points for B-Splines. The basic idea is that we want to interpolate a smooth curve into a set of points. B-Splines are a sequence of Bezier curves which solve that problem. But each Bezier curve is defined by four points: the start and end point and two control points which define the final appearance of a curve segment.

I wrote a sample program which can be downloaded directly here. If you quickly want to use it, simply look at the code and its comments. If your are interested in the background go ahead and read this article 🙂 Continue reading

Nov 23

HOWTO Render Charts With Smrender

franceThis article is a step-by-step guide to render your own sea charts. I assume that you have already installed it to your system. If not, download the latest version and run ./configure and make and make install as usual. Make sure that you have installed the packages libcairo2-dev, librsvg2-dev, and libfontconfig-dev.

You also may have a look at the detailed manual for more information. Continue reading

Nov 20

Combining ownCloud and syncthing

syncloudOwnCloud is a nice cloud solution which is based on free software. It allows companies and users to run their own cloud services thereby not loosing the control on their data. Every day this gets more and more important and you loose control if you use commercial cloud services such as Google, Microsoft, or Amazon.

OwnCloud allows to synchronize contacts, calendars, email, files, and has many more features. Unfortunately, there is no real-time background synchronization of folders, yet.

Syncthing is a folder sharing system which allows real-time synchronization of shared folders between your devices and others. Basically it works similar to Dropbox, but again, syncthing is free software, which Dropbox is not. Thus you control to who and where your data goes, which in fact is not known for Dropbox.

Combining both, ownCloud and syncthing actually adds background folder synchronization to the ownCloud features. Please also read update at the end of this article! Continue reading

Nov 19

Assembler on Arduino — Part 2

asm_symSome time ago I wrote this article about the build chain for assembler programming on Arduino. The article contained a simple blinking LED example. In the meanwhile I got several questions about Arduino and assembler.

This article is about a more mature real-world blinking LED example. You can download the full source package here which is discussed in the following. Continue reading

Oct 12

Learning C // Part III

After doing another course in C programming there is a new lesson. There are some hints on programming and most of them apply to any language, not just C. The following rules are recommendations which are true in most cases (but not all). You might also be interested in reading part I and part II of this series. Continue reading

Oct 11

Calculating Fractals With Integer Operations

(-1.82/-0.07), (-1.7/0.07)

(-1.82/-0.07), (-1.7/0.07)

It was in the late ’80s when I started to become interested in fractals. At the time then computers very unbelievable slow compared to what we have today thus I tried to speed up the algorithms in several ways.

This article is about using integer operations to calculate fractal images, more specifically I’ll explain how to replace floating point operations by integer operations (It is not about the theory behind fractals. There’s a lot literature about that.). Continue reading