How to generate star fields

I recently needed a texture for the skybox in a 3D space game.

I used this ImageMagick one-liner to generate a dotted canvas with some grey and white pixels. It displays well if the texture will be stretched.

convert -size 1600x900 xc: +noise Random -channel R -threshold 0.5% \
        -negate -channel RG -separate +channel \
        -compose multiply -composite stars.png

Alternative style

With a simple modification, the bright stars are made bigger, and the dull ones are made smaller, with only black and white used. This works well if the texture will be shrunk for display.

convert -size 800x450 xc: +noise Random -channel R -threshold 0.5% \
        -negate -channel RG -separate +channel \
        -compose multiply -composite -resize 200% \
        -threshold 10% stars-rounded.png

Full process

Although these are great one-liners, the actual process is a bit hard to follow without some smaller steps.

Here, we will generate a 150×90 star field in several steps. I’ve scaled each of these pictures to 200% of their original size and converted them to PNG for display on the web. I’ve used BMP in the commands only because it saves some plumbing around colour spaces.

Start with a blank canvas:

convert -size 150x90 xc: stars-01.bmp

Add random RGB noise:

convert stars-01.bmp +noise Random stars-02.bmp

In the red channel of the image, apply a black/white threshold: If the red channel is greter than 0.5%, it is set to the maximum, otherwise it is set to the minimum.

Mostly the red channel is now 100%, with random dots of 0%. The blue and green channels are still completely random:

convert stars-02.bmp -channel R -threshold 0.5% stars-03.bmp

Negate the image, so that the red channel is mostly 0%, with dots of 100%:

convert stars-03.bmp -negate stars-04.bmp

Extract the red channel and green channel.

convert stars-04.bmp -channel RG -separate +channel stars-05.bmp

The red channel will be dots of white:

The green channel will be random:

Multiply the channels together, so that the white dots become grey dots, each with a random brightness:

convert stars-05-0.bmp stars-05-1.bmp -compose multiply -composite stars-06.bmp

For the alternative style, scale the image up, then apply a new threshold. Brighter dots will appear as larger patches of white, while dull stars will be smaller or invisible:

convert stars-06.bmp -resize 200% -threshold 10% stars-06-rounded.bmp

How to use a Radeon graphics card on Debian 9

I have previously blogged about Radeon graphics cards on different Debian installs.

ATI has now released a new free driver which works brilliantly on Debian. In the past, Debian users had to choose between using the community-provided free software driver, or the proprietary one. Generally the proprietary driver was more feature-rich, but the free driver worked more reliably across upgrades. So now, you can safely ignore old guides and start using it.

Here’s how:

Upgrade

Make sure you are on Debian 9 (Stretch) or newer.

These steps apply to a fresh install.

Identify

You should use lspci to confirm that you have an ATI card.

$ lspci | grep Radeon
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti XT [Radeon HD 7970/8970 OEM / R9 280X]

Install firmware

You need to install a package called firmware-linux-free to get the driver working at all. If you want decent graphics performance, you will need firmware-linux-nonfree as well, which involves adding non-free sources:

nano /etc/apt/sources.list

Add the words “contrib non-free” to the end of your mirror:

deb http://.../debian/debian/ stretch main contrib non-free

Add the packages:

apt-get update
apt-get install firmware-linux-free firmware-linux-nonfree

And reboot:

reboot

What, that’s it?

Well, yes, for a fresh install that’s it. If your install is old, you might also have to remove old drivers or install the xserver-xorg-video-amdgpu and xserver-xorg-video-ati packages (in my case, these were already installed).

The Debian Wiki AtiHowto contains some more detailed information, most of which is not relevant for a simple desktop setup.

How to assemble a Linux software RAID array on a different computer

With Linux software RAID, if you ever toast your computer, you can retrieve the disks and open up the array on a different computer.

They appear as “Linux Software RAID Member” in the disk utility.

Simply install mdadm, and scan for arrays:

$ sudo apt-get install mdadm
$ sudo mdadm --assemble --scan
mdadm: /dev/md/0 has been started with 2 drives.

The array will then appear as a new disk, which can be formatted, mounted, or cloned via the usual tools.

How to set up Docker containers in Travis CI

This post outlines a method for using Docker for testing on Travis CI. It may be useful to you if you are a web application developer who uses GitHub.

I use this setup in my web-based word puzzle generator, so that every change is spun up and tested with a web browser before it is merged.

I got the idea for writing this from a few lines in the docker-compose documentation, which suggested that Docker is an easy way to perform automated testing over a running application:

$ docker-compose up -d
$ ./run_tests
$ docker-compose down

This snippet was missing some setup and an example app, but these three lines do all the heavy lifting.

The Docker setup

In order to focus on the Docker setup, I made a server which simply responds to TCP requests on port 5000 with the text “Hello World”.

This file is called server.sh, and sits in a directory called foo_server:

#!/bin/sh
while true; do
  # Send 'Hello World' to anybody who connects on port 5000
  echo "Hello World" | nc -l 5000
done

Alongside it, I added a Dockerfile to instruct docker to execute this tiny ‘application’ in a container, after installing the dependencies. This machine is built from the Docker-official Debian image:

FROM debian
ADD . /usr/share/test-server
WORKDIR /usr/share/test-server
RUN apt-get update && apt-get install --assume-yes netcat-openbsd
CMD ./server.sh

Lastly, a .dockerignore file is used to avoid loading the Dockerfile to the container:

# Ignore docker files
Dockerfile
.dockerignore

In the directory above, a simple test script, test.sh is used to see that the server is returning the expected output:

#!/bin/sh
set -e
expected="Hello World"
actual=`nc -v localhost 5000`
echo "Expecting: $expected"
echo "Server says: $actual"
if [ "$expected" != "$actual" ]; then
  echo "Test failed"
  exit 1
else
  echo "Test passed"
  exit 0
fi

Alongside the test file, a file called docker-compose.yml instructs Docker to create a container out of the foo_server example, and forward port 127.0.0.1:5000 to it.

version: '2'
services:
  foo:
    build: foo_server
    ports:
     - "5000:5000"
    container_name: foo_1

To try it out for yourself, you need a relatively recent version of Docker and docker-compose. The versions provided in Debian were not new enough to execute the examples, but the Docker project provides repos containing newer builds for Debian & Ubuntu. For my distro, the install was:

curl -sSL "https://get.docker.com/gpg" | sudo -E apt-key add -
echo "deb https://apt.dockerproject.org/repo debian-stretch main" | sudo tee -a /etc/apt/sources.list
sudo apt-get update
sudo apt-get install docker-engine
sudo pip install docker-compose

The versions this got me were docker 1.11.2, and docker-compose 1.7.1. Straight after the install, I could deploy & test an example locally:

$ docker-compose up --build -d
$ ./test.sh
$ docker-compose down

The CI setup

I’ll assume that if you’re reading this, you are familiar with the basics of Travis CI. The large block of code below is the .travis.yml file to set up the test machine, then execute the tests against a container.

---
# Use Ubuntu 'trusty' distribution
sudo: required
dist: trusty

install:
  # Update docker-engine using Ubuntu 'trusty' apt repo
  - >
    curl -sSL "https://get.docker.com/gpg" |
     sudo -E apt-key add -
  - >
    echo "deb https://apt.dockerproject.org/repo ubuntu-trusty main" |
     sudo tee -a /etc/apt/sources.list
  - sudo apt-get update
  - >
    sudo apt-get -o Dpkg::Options::="--force-confdef" \
     -o Dpkg::Options::="--force-confold" --assume-yes install docker-engine
  - docker version
  # Update docker-compose via pip
  - sudo pip install docker-compose
  - docker-compose version

before_script:
  - docker-compose up --build -d

script:
  - ./test.sh

after_script:
  - docker-compose down
...

Note: This uses Travis CI’s trusty distribution, which at the time of writing is the newest stable build platform available on Travis CI. This shipped an outdated version of Docker, which had to be installed over. Because the existing Docker was configured, I had to override a debconf prompt, which is why the apt addon syntax was not used to set up dependencies.

Result

The build result for each commit is displayed in Travis CI:

2016-06-ci-result-1

Under this, the output of the passing test script is shown, showing what has been set up:

2016-06-ci-result-2

Using this setup in practice

Moving this from a demo setup to a real setup would be fairly simple:

  1. Replace the installation with a real software stack
  2. Replace the server run with a command to serve the application (such as a Apache HTTP, Tomcat or Node)
  3. Replace the tests with real tests (such as Cucumber or Selenium).

The example in the pre-amble installs a LAMP stack and tests it with Selenium in its CI build.

If your application is a bit larger, your only extra complexity will come from running multiple containers with docker-compose.

Get the code

All of these scripts in a working CI example are available on GitHub:
mike42/minimal-docker-ci

Quick guide: Running stock Debian on the Raspberry Pi 2

At the time of writing, the ‘Raspbian’ port of Debian is often used on the Raspberry Pi. It was created to match the CPU architecture, for better performance. These reasons don’t apply to the newer Raspberry Pi 2, so if you’re a Debian desktop or server user, you can do away with the fork and just run Debian Jessie armhf.

The info from Debian is: https://wiki.debian.org/RaspberryPi2

A bit more background about why this only applies to the Raspberry Pi 2-

  • The Raspberry Pi 1 uses ARMv6 chipset with hard floats
    • The Debian armhf port requires ARMv7
    • The Debian armel port doesn’t use hard floats, so is unnecessarily slow on the Pi.
    • So Raspbian was created for the Raspberry Pi 1’s ARMv6 w/ hard-floats, and gets the most juice out of the CPU on the Raspberry Pi 1.
  • The Raspberry Pi 2 uses ARMv7 with hard floats, so Debian armhf port is fine.

Install the image

Image is linked to from this page:

I will assume that your machine has an SD card slot. To find the device name, list out disks and look for one of the correct size, which appears when you plug in the card:

df

Download a copy of the image, extract it out, and dd the file on to the card:

wget -c https://images.collabora.co.uk/rpi2/jessie-rpi2-20150705.img.gz
gunzip jessie-rpi2-20150705.img.gz 
sudo dd if=jessie-rpi2-20150705.img of=/dev/sdX bs=4M
sudo sync
umount /media/$USER/*

Plug in the Raspberry pi, and then log in. If you are using SSH, then arp-scan is a good tool to pick up devices on the network:

sudo apt-get install arp-scan
sudo arp-scan -l
ssh root@x.y.z.w

Configure pi- Things like screen resolution and HDMI go here:

cd /boot/firmware/
nano config.txt

Perform a software upgrade:

nano /etc/apt/sources.list
apt-get update
apt-get dist-upgrade

Start fixing security defaults. Remember that this is not a clean install, so start by setting your own passwords:

passwd

Check that there are no other accounts with passwords set:

cat /etc/shadow

Regenerate all SSH Server keys (commands from here):

ssh-keygen -f /etc/ssh/ssh_host_ecdsa_key -N '' -t ecdsa -b 521
ssh-keygen -f /etc/ssh/ssh_host_dsa_key -N '' -t dsa
ssh-keygen -f /etc/ssh/ssh_host_rsa_key -N '' -t rsa

Lastly, generate some locales:

sudo locale-gen en_US en_US.UTF-8 en_GB en_GB.UTF-8

How to resize a Windows VM image with virt-resize

I recently had a Windows 7 Virtual Machine stored on an undersized qcow2 file. This post steps through the simplest way that I know to produce a new, bigger disk and expand the filesystem onto it.

Empty out the empty space

Because the guest VM is stored on a QCOW2 file, we can recover un-used space on disk by zeroing it out now. Download the sdelete utility from Microsoft and run it on the system.

sdelete -z

One this is done, power off the guest.

Assuming the host is linux, you need the qemu-utls and libguestfs-tools packages to follow these steps. On Debian-

apt-get install libguestfs-tools qemu-utls

Move the VM image to a new filename and inspect it.

mv windows.img windows.img.bak

The file command indicates that the disk is about 30GB expanded.

$ file windows.img.bak 
windows.img.bak: QEMU QCOW Image (v3), 32212254720 bytes

The qemu-img command shows that the disk is 83% full:

$ qemu-img check windows.img.bak 
No errors were found on the image.
411337/491520 = 83.69% allocated, 5.66% fragmented, 0.00% compressed clusters
Image end offset: 26961969152

Check out your FS names, note that /dev/sda2 is the disk we want to up-size in this case

$ virt-filesystems -a windows.img -l
Name       Type        VFS   Label            Size         Parent
/dev/sda1  filesystem  ntfs  System Reserved  104857600    -
/dev/sda2  filesystem  ntfs  -                32105299968  -

Make a new, bigger disk image

Create a new disk of the desired size. In my case, 50G is sufficient:

$ qemu-img create -f qcow2 windows.img 50G
Formatting 'windows.img', fmt=qcow2 size=53687091200 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16

The file command shows that this new empty disk image is larger than the old image.

$ file windows.img
windows.img: QEMU QCOW Image (v3), 53687091200 bytes

Copy the old disk to the new one. The --expand option names a partition which will be grown to fill the extra space.

virt-resize --expand /dev/sda2 windows.img.bak windows.img

The virt-resize command shows a progress bar while it works, and zero-blocks will be reclaimed as a result of the output format:

2016-04-disk01

The final line of output suggests holding on to your backup until you’ve checked it, which is wise:

Resize operation completed with no errors. Before deleting the old disk,
carefully check that the resized disk boots and works correctly.

Check that the new disk is valid and contains partitions at the expected size:

$ virt-filesystems -a windows.img -l
Name       Type        VFS   Label            Size         Parent
/dev/sda1  filesystem  ntfs  System Reserved  104857600    -
/dev/sda2  filesystem  ntfs  -                53579939840  -

Boot up the guest

When the machine boots up, you may get a disk check prompt. Because the console I was using triggered the ‘Press any key to cancel’ prompt, I had to reboot and leave the console disconnected in order for the check to start.

2016-04-disk02

2016-04-disk03

After booting, the C:\ drive should display at its new size:

2016-04-disk04

Convert a PC to a HTPC with Debian and Kodi

I recently converted an old workstation to run as a home-theatre PC (HTPC). I’ve noted down the setup here for others who are making an installation like this. Some steps depend on using a radeon chipset, and will need to be adjusted for your computer.

Hardware

First up, Desktop ‘towers’ are not a good form-factor for sitting in TV cabinets. If your PC is this sort of size, then source a small form-factor case and power supply, and load the computer’s components into it:

2016-02-htpc

I also used a Logitech k400r keyboard and mouse for wireless input.

Install Debian and apps

Write the latest copy of Debian Stable to a CD or flash drive (this is version 8.3 at time of writing), and install it on the computer. Check “Debian Desktop environment” / GNOME during setup.

After installation, open a terminal, and type “su” to get root privileges.

su

Edit the software sources to include ‘contrib’ and ‘non-free’, as well as ‘jessie-backports’.

nano /etc/apt/sources.list
deb http://ftp.us.debian.org/debian/ jessie main contrib non-free
deb-src http://ftp.us.debian.org/debian/ jessie main contrib non-free

deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free

# jessie-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ jessie-updates main contrib non-free
deb-src http://ftp.us.debian.org/debian/ jessie-updates main contrib non-free

# jessie-backports
deb http://ftp.us.debian.org/debian/ jessie-backports main contrib non-free
deb-src http://ftp.us.debian.org/debian/ jessie-backports main contrib non-free

Update sources and install Kodi:

apt-get install --install-suggests kodi

Also install the firmware packages that you may need.

apt-get install firmware-linux-free firmware-amd-graphics

Tweaks

Sudo

sudo allows you to run commands as root from your regular user account. Install the package and add yourself to the sudo group:

apt-get install sudo
usermod -a -G sudo mike

To apply the change, log out and back in again. The rest of this guide assumes you are logged in as yourself, and will use sudo where necessary.

Auto-start Kodi

Open the tweak tool, and locate the list of startup programs.

gnome-tweak-tool

Add Kodi to the list, log out, log in, and Kodi will launch automatically.

Auto-login

For a PC attached to a TV, user permissions are not so importnat, so set the user to log in automatically.

sudo nano /etc/gdm3/daemon.conf

Un-comment this block and enter your username:


# Enabling automatic login
#  AutomaticLoginEnable = true
#  AutomaticLogin = user1

Plymouth start-up screen

Install plymouth and configure grub to change the Debian boot sequence (a menu with timeout, followed by lots of text) into a graphical splash screen. This takes a bit of configuration.

sudo apt-get install plymouth

Set it up according to these instructions:

sudo nano /etc/initramfs-tools/modules

Set drm correctly for your chipset:

# KMS
drm
radeon modeset=1

Configure grub:

sudo nano /etc/default/grub
...
GRUB_TIMEOUT=0
...
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
...
GRUB_GFXMODE=1920x1080
...

Update grub, set the theme in Plymouth:

sudo update-grub2
sudo /usr/sbin/plymouth-set-default-theme --list
sudo /usr/sbin/plymouth-set-default-theme joy

Run update-initramfs to apply the changes

sudo update-initramfs -u

Samba

Samba will let you share folders over your network. A basic folder with guest read/write is simple to set up:

sudo apt-get install nautilus-share samba libpam-smbpass winbind
sudo usermod -a -G sambashare mike

Log out, and back in to apply the group change, and then share the Public folder over the network by right-clicking on it and opening the “Sharing Options”:

2016-02-samba-share

Gnome will warn that the folder as shared if you open it:

2016-02-samba-shared

Test the setup by typing smb://localhost into the address bar:

2016-02-samba-test

Overscan correction

In my case, I was able to set the TV to treat the input as a “PC” input. If that doesn’t work for you, then use xrandr in a login script:

Find the name of your input:

xrandr --query

Set underscan (get the horizontal and vertical values by trial and error):

xrandr --output HDMI-0 --set underscan on
xrandr --output HDMI-0 --set "underscan hborder" 32 --set "underscan vborder" 16

Kodi plugins

Add these as needed. The Australian catchup TV plugins repository from GitHub worked well.

Kodi RSS

The RSS feed shows Kodi updates by default, and is part of your user profile.

2016-02-feed-file

Edit the configuration file, and adjust the paths to your news sources of choice.

2016-02-feed

Boot speed

Readahead is the tool of choice for boot speed optimisation. Install it, and reboot.

sudo apt-get install readahead
sudo touch  /.readahead_collect
sudo reboot

Desktop Apps

If you quit Kodi, you are dropped back to the GNOME desktop. These apps are simply to improve the desktop user experience.

Google Chrome

Download the .deb file for Chrome from Google, install with dpkg, and then clean up dependencies:

dpkg -i google-chrome-stable_current_amd64.deb 
apt-get -f install

Firefox

Download and extract the Firefox for Linux tarball from Mozilla.

Move it to /usr/share, and change the owner to match other applications there.

mv firefox /usr/share/
cd /usr/share/
ls -Ahl
chown root:root firefox
chown -R root:root firefox

Find the main menu editor, and add Firefox to the menu.

2016-02-menu

Name
Firefox Web Browser
Command
/usr/share/firefox/firefox-bin
Icon
/usr/share/firefox/browser/icons/mozicon128.png

2016-02-firefox-icon

2016-02-firefox-menu

Test the new icon by searching:

2016-02-ff

Auto-clear browser profiles

Because you don’t need a password to log in to the user account, you can add this as a bit of insurance so that your box wont remember any passwords or sessions.

crontab -e

This job removes the Firefox and Chrome user profiles each boot.

@reboot rm --preserve-root -Rf -- ~/.config/google-chrome ~/.cache/google-chrome ~/.mozilla/firefox ~/.cache/mozilla/firefox

VLC

For file format support, best to have another media player:

sudo apt-get install vlc

Result

You should now have a PC which boots into Kodi for media and TV, and lets you quit into a desktop to browse the web or run regular desktop apps.

2016-02-kodi

2016-02-gnome

On the 1GB RAM / dual core workstation, it still took around 45 seconds from the BIOS handing over control to Kodi being ready.

Update 2017-12-29: Re-installing this setup on an SSD shortened this time to 21 seconds. This includes boot, login, and an application start.

How to create an animated GIF from a series of images

Sometimes, you end up with a folder full of images, which you want to animate. With the open source ImageMagick tool, this is easy on the command line:

animate *.png

This will show you all of the PNG files in the folder in quick succession, like a flip book.

ImageMagick works on just about any OS. For Linux users, the package is generally imagemagick or ImageMagick:

sudo apt-get install imagemagick
yum install ImageMagick

But this blog post is about animated GIFs, so lets make one of those. This is a compact way to combine images (here and here for examples in context), gives you a re-usable at-a-glance illustration of something that changes over time.

Example from an older post:

2015-04-tetris

The steps to make a good conversion command are:

  1. Check that alphabetically, your images are in order. If not, rename them:
    echo *
  2. Convert them to a GIF a few times, and find the delay that suits you (hundredths of a second between frames)
    convert -delay 80 *.png animated.gif
  3. Choose an output size (width x height):
    convert -resize 415x -delay 80 *.png animated.gif
  4. Compress with -Layers Optimize for a smaller file:
    convert -resize 415x -delay 80 *.png -layers Optimize animated.gif

Notes

  • Generated thumbnails usually take the first frame only, which is why we ask Imagemagick to resize it (WordPress users: Choose “Full Size”).
  • To pause at the start of the loop for a moment, just copy the first image a few times.

How to install KA Lite on the Raspberry Pi

KA Lite is an open source, web-based learning package. Today I’ll run through a simple setup which will allow a Raspberry Pi to provide a wireless learning resource server for a classroom, without the Internet.

dia

The Raspberry Pi 2 is a surprisingly powerful single-board computer. You can use it for anything which a computer can do, in a relatively cheap circuit board the size of a credit card:

2015-06-rpi-2b

This setup takes around two hours.

Materials

You will need:

  • Raspberry Pi (The Raspberry Pi 2 Model B was used here), with micro SD card, mouse, keyboard, monitor with HDMI.
  • A good Micro USB power supply – Many Android phone chargers will be suitable.
  • A computer which can write to micro SD cards. If your computer has an SD card slot, get an SD-to-Micro-SD adapter for it.
  • A wired network with Internet for the setup
  • A USB wireless network adapter such as WiPi for deployment.
  • Any WiFi-enabled device for testing.

Install Raspbian

Raspbian is an operating system for the Pi, and is the perfect choice for embedded server setups like this. You need to write the image to the Micro SD card.

  1. Obtain the image from https://www.raspberrypi.org/downloads/
  2. This is zipped, so extract it to get the real image file.
  3. Write the disk image to the SD card:
    • Windows: Fetch a copy of “Win32 Disk Imager” to write this file to the SD card.
    • Linux or Mac: Use dd (found in the terminal) to write to the card — guide available here
  4. Boot the Pi, with mouse, keyboard, HDMI, and wired network. If it doesn’t work, remove any cable converters (use HDMI direct to monitor), and if it still doesn’t work, then the SD card was not correctly imaged.
  5. Expand root filesystem, set your password, and enable “boot to desktop”.
  6. After reboot, you should have a desktop. Click the black terminal icon to get to work.

Install some things

From the terminal, run these commands:

sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get install chromium python-m2crypto

This checks for new software (update), upgrades anything necessary (dist-upgrade), and then installs two packages:

  • python-m2crypto — this will help speed up KA Lite a bit by helping out with encryption.
  • chromium — this is Google Chrome’s open source cousin, and it’s worth installing so that you can Google things as you go, and test things locally.

If everything goes to plan, you should now be able to find Chrome on the menu and navigate the web.

2015-06-kalite-rpi-chrome

Install KA Lite

These steps are a shortened version of the official guide

Once Raspbian is running, these commands will download & install KA Lite:

git clone https://github.com/learningequality/ka-lite.git
cd ka-lite/
./setup_unix.sh

The download is 150MB, so allow a few minutes. The installer then prompts for a few questions, like:

  • “Do you wish to download the assessment package now?” — Say yes, it fetches another 500MB.
  • “Do you wish to set the KA Lite server to run in the background automatically when you start this computer?” — say “y”.

At the end, you will be given a command to start the server, which you should type in as well:

/home/pi/ka-lite/bin/kalite start

Once it starts (it will take a while!), it will give you two web addresses. One of them is local to the computer (127.x), and the other will work from other computers on the network. Write both of them down!

The install & start-up together will look like a this:

2015-06-03-kalite-install

Test it out locally

Open up Chromium, and navigate to one of the addresses that the installer suggested.

2015-06-03-kalite-1

Log in, using the details provided during the installation.

2015-06-03-kalite-2

Click on “Manage”, then “Videos”

2015-06-03-kalite-3

KA Lite will prompt for registration, which lets you download content. Use the “One click registration” on the left, then wait for it to connect.

2015-06-03-kalite-4
2015-06-03-kalite-5

Use the Videos section to fetch something. Here we fetch something from the ancient art & culture section:

2015-06-03-kalite-6

Wait a few minutes before moving to the next section: The video downloads in the background.

Access over the network

From some other device which is on the same network, enter the web address that was given at the end of the installer (ignore the address which starts with 127.x — it wont work between two computers):

http://(IP address):8008/

From the browser, let’s test it out. Click over to Learn, and navigate to the video you just downloaded. It should display, so we can learn about those Egyptian artifacts:

2015-06-03-kalite-7

This setup would be complete if you want to run on a wired network – you can simply bookmark this address on each computer which needs to use it, and manage it through the web.

Next post in this series: Raspberry Pi KA Lite wireless deployment

How to run Tetris on your Raspberry Pi

This is a simple walkthrough on how to install my Tetris clone, Blocks, on a Raspberry Pi.

On most computers running Debian (or Raspbian in the case of the Raspberry Pi), it’s as simple as clone, compile, run:

sudo apt-get install libncurses5-dev doxygen
git clone https://github.com/mike42/blocks
cd blocks
make
./bin/blocks

If you have any issues running this, then you need to fetch a newer version of GCC, as this needs C++11 support to compule (see last section for instructuins).

But if all goes to plan, you will get something like this in your terminal:

2015-04-tetris

Use the keyboard to control the game:

Move
Right, down, left
Rotate
Up
Drop
Spacebar
Quit
q

Get a screen

Basically any project with graphics can benefit from one of these. Simply add on a TFT shield, such as PiTFT to create a tiny console:

2015-04-tetris

Of course, this is still keyboard-controlled, but with some hacking, I’m sure you could map touch events to keyboard actions.

Troubleshooting: Update GCC

The Raspbian spftware image which many Raspberry Pi’s have is slightly too old to compile Blocks, which requires C++11 support.

Luckily, it’s very easy to upgrade from wheezy to jessie to add it. You know you need to do this if you get this error compiling:

$ git clone https://github.com/mike42/blocks
$ make
mkdir -p bin
g++ src/main.cpp src/blocks_game.cpp src/blocks_shape.cpp -o bin/blocks -lcurses -lrt -std=c++11 -Wall
cc1plus: error: unrecognized command line option ‘-std=c++11’
cc1plus: error: unrecognized command line option ‘-std=c++11’
cc1plus: error: unrecognized command line option ‘-std=c++11’
Makefile:2: recipe for target 'default' failed
make: *** [default] Error 1

Generally this means you don’t have GCC 4.8, which is not available in wheezy edition of Raspian.

$ g++ --version
g++ (Debian 4.6.3-14+rpi1) 4.6.3
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

So to summarise this thread, you need to:

nano /etc/apt/sources.list

Find this line:

deb http://mirrordirector.raspbian.org/raspbian/ wheezy main contrib non-free rpi

And change the word “wheezy” to “jessie”:

deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi

You can then update everything with:

sudo apt-get update && sudo apt-get dist-upgrade

You are now running the newer jessie release, which gives you access to the GCC 4.8 package we need:

apt-get install g++-4.8

So we can pick up where we left off, and compile the game:

make
./bin/blocks