Detexify - Easily find the LaTeX command you are looking for

Have you ever been searching for hours when you needed just a simple LaTeX command for a symbol? Well, this might be over now:
Check out Detexify: Just draw the symbol you need and the applet will give you possible matches for your query.

Framebuffer Manipulation with Vigra(numpy) Interface for Linux Framebuffer

I wrote an interface that allows accessing a Linux framebuffer using vigra(numpy). It is at a very early stage and lacks documentation and offers only very basic functionality (writing an array to the framebuffer) so far.
This video shows the library in action. Again, all that is included is vigranumpy and Linux framebuffer. No X or other graphics system is used.

Another video showing framebuffer manipulation in action (vigra.filters.gaussianGradientMagnitude), this time captured directly from framebuffer using ffmpeg.

As always, the code can be found on my git repository:
https://github.com/hanslovsky/rpi_st7735

Sainsmart 1.8" finally running on Arch@RaspberryPi

R and B channels are swapped, but that just requires copying the newly compiled kernel to the pi.
http://www.youtube.com/watch?v=GA3vhDO2cxs&feature=youtu.be

Acknowledgements:
I followed these instructions:
http://www.whence.com/rpi/
http://marks-space.com/2012/11/23/raspberrypi-tft/

This was neccessary in order to get the kernel to work:
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=53&t=53784

The video shown on the display is taken from:
http://hubblesource.stsci.edu/sources/video/clips/

Image source:
gramophone.co.uk

First Successful Image Operation Using Vigra On Arch@Raspberry Pi

I just applied a gaussian gradient magnitude filter on an image in vigra on arch@raspberry pi for the first time. It took me quite a while to get it running, but now Image analysis can be done on that little box.

Image Source:

gramophone.co.uk

Raspberry Pi X-Compilation using distcc

I just successfully used distcc for cross compilation for the first time on my Raspberry Pi. I am using Arch Linux both on my Pi and my desktop. You can get distcc from the official Arch repos.
Setting up distcc is not hard:
You need to edit the following files (as root):

• /etc/conf.d/distcdd (both server(s) and daemon):
• add allowed ip addresses to DISTCC_ARGS with --allow <addr>
• /etc/makepkg.conf (daemon only):
• in BUILDENV: change !distcc to distcc
• uncomment DISTCC_HOSTS and add hosts using the format <addr>/<number of threads>
• edit MAKEFLAGS to use the desired number of threads, e.g. MAKEFLAGS="-j3"
• if neccessary specifiy a PATH variable
• /etc/distcc/hosts (daemon only):
• add the hosts here (this seems redundant, but it was neccessary for me)

In order to use distcc you will need proper compilers on your hosts. For the Pi you can build your own toolchain or just download one if it's available for your platform.

Test your compiler with a small program like this (c++):

distcc c++ hello.cxx -o hello

Instructions and a cross compilation toolchain for Arch can be found here:

http://archlinuxarm.org/developers/distcc-cross-compiling

https://wiki.archlinux.org/index.php/Distcc

Python: defaultdict of defaultdict

Recently I was trying to create a nested dict (or better nested defaultdict) in Python. This is the solution that matched my needs perfectly:

 from collections import defaultdict
nested_dict = defaultdict(lambda : defaultdict(list))

The defaultdict constructor takes any factory as an argument, a requirement that can be easily be met using python lambda functions.

PyQt4: Widget that holds an image and a quit button

I made an extension to the WidgetWithQuit class I introduced recently in this post.
It now can hold an image (input should be a 2D or 3D numpy.ndarray). In WidgetWithQuit the quit button would keep its position relative to the bottom right corner. In WidgetWithPictureAndQuit the image displayed is resized likewise: It always keeps the distance to the borders and the quit button while keeping the aspect ratio. If the image, after resizing, is not centered (it happens, when it is not wide enough), it will be centered, such that the distance to the left and right border will be increased.
In addition to the usual imports, you now also need qimage2ndarray which can be installed via pip.
Please note that in order to make the example shown below work you will need the code introduced in my recent post.

from qimage2ndarray import array2qimage

class WidgetWithPictureAndQuit(WidgetWithQuit):
    def __init__(self, parent=None, buttontext="Quit", margin=10, image=None):
        WidgetWithQuit.__init__(self, parent, buttontext, margin)
        self.image = array2qimage(image)
        self.label = QtGui.QLabel(self)
        if self.image is not None:
            self.resize_image()

    def resize_image(self):
        widget_geometry = self.geometry()
        button_geometry = self.quit_button.geometry()
        width = widget_geometry.width() - 2*self.margin
        height = widget_geometry.height() - (button_geometry.height() + 3*self.margin)
        width_offset = self.margin
        pixmap = QtGui.QPixmap.fromImage(self.image).scaled(width, height, QtCore.Qt.KeepAspectRatio)
        if pixmap.width() < width:
            width_offset = (widget_geometry.width() - pixmap.width())/2
        self.label.setGeometry(width_offset, self.margin, width, height)
        self.label.setPixmap(pixmap)

    def resizeEvent(self, event):
        WidgetWithQuit.resizeEvent(self, event)
        self.resize_image()