Posted on December 18, 2018 by Paul
In this article, I will show you how to cross compile the latest version of OpenCV for Raspberry Pi and BeagleBone Black. At the time of this writing, OpenCV is at version 4.0.0 while the version available with the default Debian based OS on Raspberry Pi and BeagleBone Black is 2.4.9. Building OpenCV 4 directly on a Raspberry Pi or BeagleBone Black is doable, but it could take a few hours. Cross compiling OpenCV for armhf is a 20 - 30 minutes process, depending on the speed of your computer it could be even shorter.
I recommend that you do the build in a Debian Stretch virtual machine or a Docker container in order to not mess your system. If you decide to install Stretch in a virtual machine, make sure to use the minimal netinst system. It is really important that you start with a bare bone system, because we need to install armhf executables and libraries. By using a minimal system we avoid potential conflicts with the native x86-64 versions.
For the remaining of this article, I will mention only Raspbian and Raspberry Pi, if you are using a BeagleBone Black everything should work the same.
I’ll assume that you have a clean Raspbian install. I’ve used the latest available desktop image. In principle you should be able to follow the article using Raspbian Lite, but I did all my tests using the full desktop version of Rasbian.
Posted on December 7, 2018 by Paul
This is a short article about sharing your Internet connection through USB with a Raspberry Pi Zero. The procedure presented here will work with all versions of Raspberry Pi Zero (with or without onboard WiFi). You will need a Raspberry Pi Zero, a micro SD card and a USB to micro USB data cable.
Start by downloading the latest Raspbian image, I’ve used Raspbian Stretch Lite. Once the download is finished, extract the archive and flash it to your micro SD card. The Etcher flasher app works on macOS, Windows and Linux.
Posted on December 4, 2018 by Paul
This is a short article about sharing your Internet connection with a BeagleBone Black through USB on macOS Mojave. I assume that you’ve gone through the Getting Started setup and that you’ve installed the latest Debian image on your BBB.
Connect the BBB to your Mac through USB and start the device. Once the device is on, open a Terminal and use ssh to connect to your BBB:
Posted on November 19, 2018 by Paul
In this article, I will show you how to implement a BMP image loader from scratch in C++. BMP is one of the oldest image formats on the Windows platform and it is supported on most other operating systems. BMP can store two-dimensional raster images with optional compression and transparency. In this article, we will implement a simplified version of the BMP format specification that will support only 24 and 32 bits depth images in the BGR and BGRA color spaces. To make our life simpler we can also ignore the, optional, compression component.
Even if you don’t plan to use BMP images, it is still a useful programming exercise to write a BMP reader/writer in C++.
From a programming point of view, a BMP file is a binary file in the little-endian format. For our purposes, we can divide a BMP image in four regions:
- file header - all BMP images starts with a five elements file header. This has information about the file type, file size and location of the pixel data.
- bitmap header - also named the info header. This has information about the width/height of the image, bits depth and so on.
- color header - contains informations about the color space and bit masks
- pixel data.
Posted on September 28, 2018 by Paul
Updated 15 May 2019
This is a short note about getting started with Java 11 LTS or Java 12 on macOS. As you probably know, starting with Java 11 there was a big change in the license under which the official Oracle JDK is provided. In short, you need to buy a license from Oracle if you want to use the official JDK in a commercial setting. As far as I know, using Oracle’s JDK on your private computer for testing and learning purposes is allowed.
That being said, for most users OpenJDK is the new JDK of choice, it is provided under an open source license and you don’t need to pay for using it.
Posted on September 23, 2018 by Paul
The famous FizzBuzz interview question asks to print all numbers from 1 to 100. If a number is divisible with 3 print fizz, if the number is divisible with 5 print buzz and if the number is divisible with both 3 and 5 print fizzbuzz. Writing a program for the above problem is trivial. A more interesting problem is to generate the solution for the FizzBuzz problem at compile time.
In C++ we use the constexpr specifier for a variable or a function that needs to be evaluated at compile time.
Posted on September 22, 2018 by Paul
In this article I will show you how to install the latest stable version of Ruby, which is 2.5.1 at the time of this writing, on macOS, Windows 10 and Ubuntu 18.04.
- Ruby 2.5 on macOS
- Ruby 2.4 on Windows 10 native install
- Ruby 2.5 on Windows 10 with WSL
- Ruby 2.5 on Ubuntu 18.04
Posted on August 13, 2018 by Paul
In this article I will show you how to create a simple F# console application that runs on .NET Core and how to generate executables for various operating systems.
Start by downloading the .NET Core SDK for your operating system from https://www.microsoft.com/net/download. Run the installer and accept the default settings.
Posted on August 7, 2018 by Paul
In this article I will show you how to build the Boost libraries under macOS with GCC 8 or Clang. Once the libraries are installed, we’ll test the build with a short demo of using Boost Filesystem.
First, you will need to download the latest stable version of Boost, I will use version 1.68.0. Extract the archive and open a Terminal in the Boost folder.
Posted on May 6, 2018 by Paul
Updated 4 May 2019
In this article, I will show you how to build GCC 9 as a cross compiler for Raspberry Pi. A cross compiler is a compiler that runs on an operating system and produces executables for another. This is really useful when you want to use your beefy computer to build a library or other large piece of code for Raspberry Pi. As a practical example, at the end of the article, I will show you how to use the cross compiler to build GCC itself as a native Raspberry Pi application.
Part of this article is a compilation of what I’ve learned reading other people posts. Here is a list of the sources I’ve used:
From the above list, the first article is the one that is the most complete and, if you follow it, you end up with a cross compiler that partially works. To be fair, the article wasn’t written for Raspberry Pi. I recommend that you read it if you want to see a more in depth explanation of certain steps of the process.
Posted on April 25, 2018 by Paul
Updated 26 June 2019
This is a short article about installing NumPy, SciPy, Matplotlib and OpenCV on the latest Ubuntu LTS, which at the time of this writing is 18.04. Ubuntu 18.04 comes with Python 3.6.8, but I will show you how to install Python 3.7.3, which at this time it is the latest stable version of Python.
Let’s start by making sure we have an updated system:
In the first part of this article, I will show you how to install Python 3.7 and how to create a virtual environment in which we’ll install NumPy, SciPy and Matplotlib. In the second part of the article, I will show you how to, optionally, install OpenCV 4.
There is also a video version for the first part of the tutorial:
Posted on April 22, 2018 by Paul
Updated 24 March 2019
In this article I will show you how to install Clang 8 on your Raspberry Pi system and how to compile C++17 programs. At the time of this writing Raspbian is based on Debian Stretch, which comes with the stable but slightly outdated GCC 6.3 as the default C and C++ compiler. If you prefer to use GCC 8 I wrote an article about installing GCC 8 on Raspberry Pi.
There is also a video version of this tutorial:
Let’s start the installation process. Open a Terminal and download the official binary of Clang 8 for Raspberry Pi:
Posted on April 21, 2018 by Paul
In my last tutorial I’ve shown you how to create a minimal Tkinter application: load an image with OpenCV, plot the image on a Tkinter window and apply a blur filter when the user presses a button. Another interesting application is to show a camera feed or an exiting video on a Tkinter window.
Posted on April 20, 2018 by Paul
This is a short tutorial about using Tkinter, the default Python GUI library, with OpenCV. On Windows, Tkinter is bundled with the official Python installer. On Linux, you can install Tkinter using your distribution package manager. The situation is a bit more complex on macOS, that comes with Python 2.7 and an old version of Tkinter, at the time of this writing, the easiest path is to install Miniconda Python 3 that comes with the latest Tkinter.
OpenCV includes some rudimentary GUI capabilities, useful if you need to show a video or an image, get the mouse or the keyboard input. But, if you need something more complicated like buttons, drop down lists, menus, labels, text boxes and so on, you need to use a dedicated GUI library like Qt or Tkinter.
In the remaining of this article, I’ll assume that you have Python 3.6, Tkinter 8.6 and OpenCV 3.3 or newer installed on your machine. If you need help to install the above on Windows, macOS or Linux check my previous articles.
Posted on January 12, 2018 by Paul
- Part 1 - Generate and use a simple function at runtime
- Part 2 - Call a C++ function from a function generated at runtime
In my last article, I’ve shown you how to generate the machine code for a function at runtime, copy this code in a part of the memory, marked as executable, and call it from C++. Now, we’ll go the other way around, we’ll call a C++ function from a function generated at runtime. Like before, I assume that you try the code on Linux or macOS.
If you remember from part 1, we’ve started by adding machine code instructions in an std::vector and copying this code to an executable memory page. While this was a fine approach from a didactic point of view, in practice, you will probably want to write the code directly to the executable memory. Here is an example of how I propose to do it:
The object mp, from the above piece of code, will ask the OS for memory, release this memory when it is not needed and will have some helper member functions that will let us push pieces of machine code to the executable memory. We can also add safety features, e.g. a mechanism to check if we can push more data on the executable memory or if we’ve reached the bounds of the allocated memory pages.