How to compile a C++11 app on Travis CI

Posted on

I have recently been adding Travis CI builds to code that I host on GitHub, so that I don’t need to host my own build infrastructure.

To users, this just means that there is a green badge at the top of the README, but not much else:

passing.svg

To build a simple C++ project, I added in this .travis.yml file:

langauge: cpp
sudo: false

addons:
  apt:
    packages:
      - libusb-1.0-0-dev

script:
  - make

Unfortunately, on this infrastructure, the default build tools are currently ancient, and installed on Ubuntu Precise (12.04):

$ make
g++ src/missile.cpp examples/basic-sync/basic-sync.cpp -o bin/basic-sync -lpthread -lusb-1.0 -std=c++11 -Wall
cc1plus: error: unrecognized command line option ‘-std=c++11’
cc1plus: error: unrecognized command line option ‘-std=c++11’

Option 1: Update the toolchain

There is some structures you can use to install an extra repository and some named packages, instead of using apt-get directly.

langauge: cpp
sudo: false

addons:
  apt:
    sources:
    - ubuntu-toolchain-r-test
    packages:
    - gcc-4.8
    - g++-4.8
    - libusb-1.0-0-dev

script:
  - make

Because the old version was still installed, I had to refer to the exact version in the Makefile, as in:

g++-4.8 src/missile.cpp examples/basic-sync/basic-sync.cpp -o bin/basic-sync -lpthread -lusb-1.0 -std=c++11 -Wall

Option 2: Update the platform

You can also change to a more recent Ubuntu distribution. Presumably Ubuntu Precise is only the default because existing builds use it.

If you need to build C++11 apps on Travis CI, then builds will work under Ubuntu Trusty (14.04), which happens to be the newest distribution currently available:

langauge: cpp
sudo: required
dist: trusty

addons:
  apt:
    packages:
      - libusb-1.0-0-dev

script:
  - make

How to edit emulator flags in Android Studio

Posted on

I’ve recently updated to the new IntelliJ-based Android studio 2.1.

I ran into some issues attempting to launch a “hello world” project in the emulator, which I’m writing up here for the benefit of others.

For context, I run Debian GNU/Linux Jessie on an AMD64 box, with Radeon graphics card, using the free drivers.

The OpenGL error

2016-05-22-android-1

When attempting to launch a simple project with the emulator, the emulator died with the following message:

Cannot launch AVD in emulator.
Output:
libGL error: unable to load driver: radeonsi_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: radeonsi
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
X Error of failed request:  GLXBadContext
  Major opcode of failed request:  155 (GLX)
  Minor opcode of failed request:  6 (X_GLXIsDirect)
  Serial number of failed request:  49
  Current serial number in output stream:  48
libGL error: unable to load driver: radeonsi_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: radeonsi
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
X Error of failed request:  GLXBadContext
  Major opcode of failed request:  155 (GLX)
  Minor opcode of failed request:  6 (X_GLXIsDirect)
  Serial number of failed request:  49
  Current serial number in output stream:  48
libGL error: unable to load driver: radeonsi_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: radeonsi
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast
X Error of failed request:  BadValue (integer parameter out of range for operation)
  Major opcode of failed request:  155 (GLX)
  Minor opcode of failed request:  24 (X_GLXCreateNewContext)
  Value in failed request:  0x0
  Serial number of failed request:  33
emulator: WARNING: VM heap size set below hardware specified minimum of 228MB
emulator: WARNING: Setting VM heap size to 384MB
  Current serial number in output stream:  34
QObject::~QObject: Timers cannot be stopped from another thread

The console logs that the command being executed is:

/home/mike/Android/Sdk/tools/emulator -netdelay none -netspeed full -avd Nexus_5X_API_23

Fixing on the command-line

Quick list of things that didn’t work:

  • Installing more libraries via apt-get
    apt-get install libstdc++6 xserver-xorg-video-radeon
  • Pre-loading libraries
    LD_PRELOAD='/usr/lib64/libstdc++.so.6' /home/mike/Android/Sdk/tools/emulator -netdelay none -netspeed full -avd Nexus_5X_API_23
  • Attempting to understand LibGL’s debug output
    LIBGL_DEBUG=verbose /home/mike/Android/Sdk/tools/emulator -netdelay none -netspeed full -avd Nexus_5X_API_23

But the solution turned out to be this very specific flag:

$ ./emulator -help | grep libstdc++
    -use-system-libs               Use system libstdc++ instead of bundled one

So launching the emulator from the CLI worked for me, using this command:

/home/mike/Android/Sdk/tools/emulator -netdelay none -netspeed full -avd Nexus_5X_API_23 -use-system-libs

Fixing in the IDE

So this was fantastic progress, but without being able to launch this emulator from Android Studio, the development environment wasn’t really integrated yet.

Apparently there used to be a feature for adding command-line flags to the emulator, but this is now gone.

So, adapting a post here, I jumped in and replaced the emulator binary into a wrapper to inject some flags.

 $ cd ~/Android/Sdk/tools/
$ mv emulator emulator.0
$ touch emulator
$ chmod +x emulator

I then opened up the emulator in a text editor and punched in this:

#!/bin/sh
set -ex
$0.0 $@ -use-system-libs

Result

Success!

2016-05-22-android-2

Convert a PC to a HTPC with Debian and Kodi

Posted on

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.

Fix merge conflicts in git with Meld

Posted on

When you’re writing code collaboratively, there’s plenty of situations when you need to combine two sets of changes.

This could happen, for example, if Bob and yourself both fix different bugs by making edits to the same file.

foo

This post assumes that your source code is tracked in git.

First up, install meld. The Meld homepage has instructions for other platforms, but on Debian/Ubuntu, it’s just:

sudo apt-get install meld

Now tell git to use it as a tool:

git config --global merge.tool meld

Once you have a merge conflict, you can then fire up Meld like this:

git mergetool

For each file, you will get a 3-way diff. Click the arrows on the sides to move the code you want into the middle:

2015-10-meld

Once you’ve saved the file and closed Meld, you will be prompted on the command-line. You just tell it whether you’ve successfully merged the file, until it stops giving you new files to merge.

After this, commit the changes:

git commit

Done!

Simpler usage

If you don’t use git, you can simply call Meld from the command-line as well. This shows you differences between files in a similar window, and lets you move blocks of code around as well:

meld foo.c bar.c

A Yes/No filtering tool for images

Posted on

While collecting very large numbers of screen captures for writing documentation, I noticed that it takes far too long to filter out the junk.

To fix this, I coded up yn (source code via github). Given a list of images, it will display each one to the user, which they then include by pressing Y (yes) or exclude by pressing N (no) (hence the name yn).

The images which are selected are saved as a list, so that a script can continue by processing them in some way. This could be by copying them elsewhere, or generating a document with spaces to caption them. The example in the README.md does both of these.

The code to this early version is very simple, which makes it a good example of a simple OpenCV C++ app. I’ve stepped through it below.

The code

C++ does console input and output via the iostream library:

#include <iostream>

To use OpenCV with a GUI, you need these headers. You then need to add them to your include path, and link to OpenCV for the program to compile:

#include <cv.h>
#include <highgui.h>

This line simly tells the compiler that when we say cout (console out), we mean std::cout.

using namespace std;

The only OpenCV code is in the below function. The steps are:

  1. load an image from a file via imread(),
  2. display it in a window with imshow(),
  3. capture the next keypress with waitKey(), then
  4. delete the window with destroyWindow()
/**
 * Load a file, and wait for the user to press a key.
 *
 * If the pressed key is 'y', print the filename.
 */
bool yn(string fn) {
    cv::Mat img;
    char key = 0;

    img = cv::imread(fn);
    if(!img.data) {
        cerr << "Failed to load " << fn << endl;
    } else {
        cv::namedWindow(fn);
        cv::imshow(fn, img);
        key = cv::waitKey(0);
        cv::destroyWindow(fn);
        if(key == 'y') {
            cout << fn << endl; // 'y' pressed
        } else if(key == 0x1B) {
            return false; // ESC pressed
        }
    }
    return true;
}

So with that library usage out of the way, all we need to do is get the list of files to check, and stop popping up windows when the user has pressed the escape key.

/**
 * Get list of files from command-line arguments and display them in turn
 */
int main(int argc, char** argv) {
    int i;

    /* Command-line arguments given */
    for(i = 1; i < argc; i++) {
        if(yn(string(argv[i])) == false) {
            cerr << "Quitting.\n";
            break;
        }
    }

    return 0;
}

Next

The delay between images appearing can be removed by loading them in a separate thread, which I may do in a future version.

Finding prime numbers

Posted on

It’s not so hard to calculate small-ish primes. The below method is called a prime sieve, and can be done manually:

Take two, the smallest prime number.
We know that no multiples of two are prime (4, 6, 8, 10, 12 etc), so we can cross them off our list and just print two.
Then we go to 3. 3 is prime. But 6, 9, 12 and 15 can’t be, so we print 3 and cross those multiples off.
4 has been marked as not prime, so we skip it.
5 is prime, so we cross off 10, 15, 20.
so on and so forth

Computers are much better at this than humans though, so I wrote this algorithm up in java. You can find all primes up to n fairly quickly (for small values of n).

class Primes {
	public static void main(String[] args) {
		int searchMax = 16777216;
		if(args.length == 1) {
			/* Allow over-riding the maximum */
			searchMax = Integer.parseInt(args[0]);
		}
		boolean[] isprime = new boolean[searchMax];

		int i, tmp, count = 0;

		/* Initialise */
		isprime[0] = isprime[1] = false;
		for(i = 2; i < searchMax; i++) {
			isprime[i] = true;
		}

		/* Main loop */
		for(i = 2; i < searchMax; i++) {
			if(isprime[i]) {
				System.out.println(i);
				count++;
				tmp = i * 2;
				while(tmp < searchMax) {
					isprime[tmp] = false;
					tmp += i;
				}
			}
		}
		System.err.println("Found " + count + " primes between 1 and " + searchMax + " non-inclusive");
	}
}

Of course, the limitation of this is that java isn’t terribly good at handling larger arrays, so I wouldn’t expect more than a few million primes from this code.

Update: The above code was tested for finding the first 7 million prime numbers.

Gettting lost with depth-first search

Posted on

I was thinking about how to make mazes, and ended up making a maze generator.

It’s based on ‘depth-first search’, a recursive algorithm to make a spanning tree. Example output below:

Unfortunately for us, java doesn’t particularly like deep recursion, so this generator will fizzle out with an error on really big mazes. On the other hand, it can produce output as HTML:

You can download the maze generator here:

It’s a command line program. From the terminal, the usage is like this:

java -jar MazeGenerator.jar [width] [height] [formatting]

Width/height will change the size of your maze. You can set the format to ‘html’, or type in a character for the filled-in blocks to be. (The default is u2588 ‘Solid block’).