EyeLogic SDK  1.1.5
EyeLogic SDK Documentation (C++)



The EyeLogic Software Development Kit (SDK) is a free software package for building custom applications which use an EyeLogic eye tracking device. It offers the possibility to connect with your device via an application programming interface (API) from any custom application. The EyeLogic SDK is available for the programming languages C++, C#, C, and Python. It is also usable with any other programming language that is capable of importing dynamic link libraries (DLLs), e.g. Visual Basic or Matlab.

For each directly supported language, there is a short and simple sample program to help you get started with the development of your first EyeLogic application.

This guide describes the use of the EyeLogic API for C++ and gives a step-by-step introduction on how to start with your own C++ program.

System Requirements

For the system requirements of the EyeLogic Server and an installation guide, please refer to the Server's documentation.

The SDK has no additional requirements. It is built for Microsoft Windows only (32 bit or 64 bit). The included sample projects are written for Microsoft Visual Studio 2017 or newer. Any other compilers are not yet supported.

Installation and Getting Started

Download Software

In order to use an EyeLogic eye tracking device from within your application, you need the EyeLogic Server and the EyeLogic SDK. Check the download-page to get the latest release of both packages: https://www.eyelogic.de/downloads/


The software is written to support backwards-compatibility, i.e. an update of the EyeLogic Server software will not break support for your device, irregardless of the model. The actual guide assumes that you are installing the newest version of the EyeLogic Server. Please always update to the newest server version before reporting an error to the EyeLogic support.

On the other hand, updating the SDK and API-DLLs is not always neccessary. Since you as a programmer would have to recompile your application with every SDK-update, we designed the SDK such that the server is able to communicate with older API versions. Therefore, when shipping your application, just add the EyeLogic API DLLs of the actual version to your package. It is compatible with servers of the actual and newer releases.

See Shipping your Application for a tutorial on how to ship your application.

Install EyeLogic SDK on Windows

The EyeLogic SDK does not need to be installed. It ships as .zip file which just needs to be extracted to some directory on your hard disk. Be sure, that you have user-rights to that directory, e.g. any directory inside C:\Program Files or similar is problematic, since it requires admin rights to access those files every time you start your program. It is recommended to use a user-local directory.

Note: The SDK has to be installed on the same computer as the server. Please see the main server manual for help on installing the server.

After extracting the .zip file, the directory contains one subfolder for each supported programming language. Open the cpp folder, the content should be:

  • bin - contains the binary DLLs to link against
  • example - contains the sample code
  • include - contains the include header files for compilation

Getting Started with the Sample Code

In the directory, into which you unpacked the SDK EyeLogicSDK, navigate to the sub-directory cpp/example and open the solution file DemoClient.sln in Visual Studio. Note, you will need Visual Studio 2017 or newer to open this file.

You may want to choose your destination compile level (Debug/Release) in the drop down list on top of the screen. Set it to "Debug" while developing your app. When your app is finished, set it to "Release" to create an optimized application binary. Then compile from the menu with Build->Build Solution. You should see an output similarly to:

1>------ Build started: Project: DemoClient, Configuration: Debug x64 ------
1>DemoClient.vcxproj -> ...\cpp\example\x64\Debug\DemoClient.exe
1>Copy dll dependencies for execution
1>        1 File copied.
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

Before running the application check that the EyeLogic Server is running (see the EyeLogic Server manual). If the server is running, there is an EyeLogic icon in the windows tray bar.

Press F5 to compile and run the application. ...

Note that your firewall might block the connection between your program and the server. In this case, add a rule to your firewall to allow your application to open TCP/UDP ports to an application on localhost (for the windows defender, just click "accept").

If you reached this point, you have properly set up your EyeLogic SDK. You may now start with the development of you own application. See the next section Concepts for the basic programming concepts and for a tutorial on how to deploy and ship your application.


Server-Client Setup

The EyeLogic software consists of two main parts: The server and the API. The server is the neccessary driver for your eye tracking device. It detects your device and handles the communication. The API is part of the EyeLogic Standard Development Kit (SDK). It consists of .dll files which can be used by your application to set up a connection to the EyeLogic Server, start tracking and receive eye tracking data.

The server is designed to run permanently on your computer as a background process. While not actively tracking the server requires an insignificant portion of your computer's resources. Once an EyeLogic eye tracking device is plugged in, the server application detects it automatically and allows the user to set it up via the servers' configuration dialog (see the server icon in the windows tray bar). If for any reason the server background process is not running (the tray icon is missing), you may start the server manually via the windows start menu.

The API is a set of .dll files which can be used by any custom program (called the user application). With these DLLs the user application can establish a connection to the (running) server via the TCP protocol.

Set Up a Project for your Application

For an easy start to develop a new application it is recommended to copy the existing sample folder to a new location (e.g. EyeLogic_SDK\cpp with all its contents). The sample source file already provides a fully functional implementation. Starting from this sample code, you can easily modify and extend the code to suit your customized experiment.

Alternatively you can start a new Visual Studio project from scratch. In that case be sure the compiler and linker are able to find the EyeLogic include and binary files. Therefore, apply the following changes to the project properties of your Visual Studio project:

  • Under "C/C++", set "Additional Include Directories" to the location of <Location of your EyeLogic_SDK>\cpp\include.
  • Under "Linker", set "Additional Library Dependencies" to <Location of your EyeLogic_SDK>\cpp\bin.
  • Under "Linker -> Input", add ELApi.lib to "Additional Dependencies" (for Win32-Applications, use ELApi32.lib).

Control Flow between API and server

The usual control flow between the custom application/API and the server is characterized by the following steps:

  1. initialize: Before calling any other function the API DLLs need initializing.
  2. connect to server: Establish a connection to the server via TCP.
  3. find eye tracking device: Obtain the information on connected eye trackers, otherwise wait until an eye tracker is plugged in.
  4. start tracking: Request tracking. If successful, the device will start tracking and the server sends GazeSamples to the user application, see also GazeSamples.
  5. perform calibration: Request a calibration. The screen will show a calibration point animated to be moving across the screen. The user must fixate on this point until the calibration screen diappears. The system is calibrated and ready to use once this process is completed sucessfully.
  6. shut down: At the end of your experiment either stop the tracking or simply shutdown the API.

All information which is passed from the server to the user application will be transmitted via asyncroneous callbacks. The application has to register it's own implementations of those callback functions with the API (see Example Program for an example implementation).

Note that you need to calibrate in order to obtain valid gaze samples (see GazeSamples). All gaze samples which are reported before the system is calibrated contain no valid eye data.

Example Program

In this section, the code of the C++ example program is explained in some detail.

The file starts with an include section. It adds

#include "elapi/ELApi.h"

in order to find all neccessary definitions of the EyeLogic API.

Gaze samples and events are populated by asyncroneous callbacks. They are defined further below by deriving from the interfaces elapi::ELApi::ELGazeSampleCallback and elapi::ELApi::ELEventCallback.

Events are invoked whenever something on the external state changes, e.g. a new eyetracking device is plugged in. The definition of the event receiver is:

class EventReceiver : public elapi::ELApi::ELEventCallback
    onEvent( elapi::ELApi::Event event ) override { ... }

and the definition of the gaze sample receiver is:

class GazeSampleReceiver : public elapi::ELApi::ELGazeSampleCallback
    onGazeSample( const elapi::ELGazeSample& gazeSample ) override { ... }

The example code simply prints incoming gaze samples and events to the console.

In the main( ) method the application implements its control flow. It consists of the following code lines:

DeviceListener deviceListener;
elapi::ELApi   api( "Demo Client" );
auto eventReceiver = std::make_unique< EventReceiver >( api );
api.registerEventListener( eventReceiver.get( ) );

This constructs a new instance of the ELApi class. The instanciation will automatically initialize the library and it will also be automatically deinitialized when object api goes out of scope. The call of registerEventListener registers the own instance of the event callback to the EyeLogic API. From now on, any incoming events will invoke the onEvent( ) method from the code above.

const auto retConnect = api.connect( );

Connects to the EyeLogic server. Check for the return value in order to find out whether the connection was established successfully.

api.getScreenConfig( screenConfig );


api.getDeviceConfig( deviceConfig );

are called in order to obtain information about the active screen and the connected eye tracking device.

const auto retStart = api.requestTracking( 0 );

Tells the device to start tracking and the Server to begin sample processing. The parameter 0 specifies the frame rate mode. If your device is capable of multiple frame rate modes (60Hz, 120Hz or 250Hz), you can also enter a different number. The list of available frame rate modes is part of the DeviceConfig and can be obtained by calling getDeviceConfig(). The first frame rate mode (DeviceConfig.frameRates[0]) is the default mode, which usually is the highest available speed mode of your system.

const auto retCalibrate = api.calibrate( 0 );

Performs a calibration. This method blocks until the calibration ends - i.e. completed or aborted. The parameter 0 denotes the type of calibration. A list of available calibration methods is part of the DeviceConfig and can be obtained by calling getDeviceConfig( ).

The example program waits for 10 seconds and then closes the connection:

api.disconnect( );
api.registerGazeSampleListener( nullptr );
api.registerEventListener( nullptr );

The last two lines unregister the callback functions. Be sure to unregister them before destroying the API object.


GazeSamples are the most essential data which is generated by the eye tracker. The eye tracker delivers one GazeSample per frame. Each sample contains information on the time of measurement, the position of the eyes, the pupil radius and the point where the user looks at on some stimulus plane (usually a computer monitor).

Shipping your Application

When you want to ship your application, be sure to include all relevant files so that it may run on different computers. The EyeLogic functionality will only work on computers which have the EyeLogic Server installed. The installed server needs to at least be of the same version as the shipped API DLLs (a newer server version is permissible).

Beside the relevant files of your application, you need to ship the content of the bin/ folder of your language (typically including some .dll files). Place the content of the bin/ folder inside the working directory of your application and ship them together.


License Agreement and Warranty for SDK


The License Agreement is a legal agreement between you and EyeLogic GmbH and its affiliates (“EyeLogic”, “we”, or “us). This license agreement governs your use of the EyeLogic software and any third party software that may be distributed therewith (collectively the “software”). EyeLogic agrees to license the software to you (personally and/or on behalf of you employer) (collectively “you “ or “your”) only if you accept all the terms contained in this license agreement. By installing, using, copying, or distributing all or any portion of the software, you accept and agree to be bound by all of the terms and conditions of this license agreement.

If you do not agree with any of the terms of this license agreement, do no install or use the software.

  1. License Grant: EyeLogic grants you a revocable, nonexclusive, non-transferable, limited right to install and use the application on a device owned and controlled by you, and to access and use the application on such mobile device strictly in accordance with the terms and conditions of this licenses, the usage rules and any service agreement associated with your device. The Software includes third party software and other copyrighted material. Acknowledgements, licensing terms and disclaimers for such Third Party Software are provided with the Software or contained in the Documentation, and your use of such Third Party Software is governed by their respective terms (collectively “Related Agreements”).
  2. Restriction on Use: You shall use the application strictly in accordance with the terms of the related agreements and shall not:
    1. decompile, reverse engineer, disassemble, attempt to derive the source code of, or decrypt the application,
    2. make any modification, adaption, improvement, enhancement, translation or derivative work from the application,
    3. violate any applicable laws, rules or regulations in connection with your access or use of the application,
    4. remove, alter or obscure any proprietary notice (including any notice of copyright or trademark) of EyeLogic or its affiliates, partners, suppliers or the licensors of the application,
    5. use the application for any revenue generating endeavor, commercial enterprise or other purpose for which it is not designed or intended,
    6. make the application publicly available over a network or other environment permitting access or use by others without the written permission of EyeLogic,
    7. use the application for creating a product, service or software that is, directly or indirectly, competitive with or I any way substitute for any services, product or software offered by EyeLogic,
    8. use any proprietary information or interfaces of EyeLogic or other intellectual property of EyeLogic in the design, development, manufacture, licensing or distribution of any applications, accessories or devices for use with the application.
  3. Termination: EyeLogic may, in its sole and abolsute discretion, at any time and for any or no reason, suspend or terminate this license and the rights afforded to you hereunder with or without prior notice. Furthermore, if you fail to comply with any terms and conditions of this license, then this license and any rights afforded to you hereunder shall terminate automatically, without any notice or other action by EyeLogic. Upon the termination of this license, you shall cease all use of the application and uninstall the application.
  4. Disclaimer of Warranties: You acknowledge and agree that the application is provided on an “as is” and “as available” basis, and that your use of or reliance upon the application and any third party content and services accessed thereby is at you sole risk and discretion. EyeLogic and its affiliates, partners suppliers and licensors hereby disclaim any and all representations, warranties and guaranties regarding the application and third party content and services, whether express, implied or statutory, and including without limitation, the implied warranties of merchantability, fitness for a particular purpose, and non-infringement, furthermore, EyeLogic and its affiliates, partners, suppliers and licensors make no warranty that

    1. The application or third party content and services will meet your requirements,
    2. The application or third party content and services will be uninterrupted, accurate, reliable timely secure or error-free,
    3. The quality of any products, services, information or other material accessed or obtained by you through the application will be as represented or meet your expectations, or
    4. Any errors in the application or third party content and services will be corrected.

    No advice or information whether oral or written, obtained by you from EyeLogic or from the application will create any warranty not expressly made herein or create any liability on the part of EyeLogic.

    If the licensee modifies or replaces any of the third party open source software included in the software, EyeLogic is not obligated to provide any updates, maintenance, warranty, technical or other support or services for the resultant modified Software. You expressly acknowledge that any failure or damage to any hardware, software or systems as a result of such modification to the open source components of the software is excluded from the terms of any EyeLogic warranty.

  5. Limitation of liability: Under no circumstances shall EyeLogic or its affiliates, partners, suppliers or licensors be liable for any indirect, incidental, consequential, special or exemplary damages arising out of or in connection with your access or use of or inability to access or use the application and any third party content and services, whether or not the damages ere foreseeable and whether or not EyeLogic was advices of the possibility of such damages. Without limiting the generality of the foregoing, EyeLogic’s aggregate liability to you (whether under contract, tort, statue or otherwise) shall not exceed the amounts actually paid by licensee for the licensed materials. The foregoing limitations will apply even if the above stated remedy fails of its essential purpose.
  6. Confidentiality: Licensed materials are proprietary to EyeLogic and constitute EyeLogic trade and business secrets. The licensee shall maintain licensed materials in confidence and prevent their disclosure using at least the same degree of care it uses for its own trade and business secrets, but in no event less than a reasonable degree of care. The licensee shall not disclose licensed materials or any part thereof to anyone for any purpose, other than to its employees and sub-contractors, if any, for the purpose of exercising the rights expressly granted under this agreement, provided they have in writing agreed to confidentiality obligations at least equivalent to the obligations stated herein. The foregoing does not apply to information that a. is or becomes generally known or available to the public without any breach of the confidentiality obligation by licensee, b. was already known to licensee prior to the disclosure by EyeLogic, or c. was rightfully acquired by licensee from a third party without a breach of a confidentiality obligation towards EyeLogic. In case of a dispute, the licensee has the burden of proof that the licensed materials and/or any portion thereof fall under one of these exceptions. Should the licensee be legally compelled to disclose any licensed materials to a third party, such as pursuant to a mandatory order by a court or authority or any comparable action, the licensee shall, to the extent permitted under applicable law, inform EyeLogic without undue delay and undertake all possible measures to safeguard secrecy.

About EyeLogic

EyeLogic is a manufacturer of high precision and high quality eye tracking devices, mainly for scientific and research use cases. EyeLogic GmbH is a spin-off of the Free University of Berlin, faculty of mathematics and computer science and has a vast experience in image processing and computer vision.

Contact and Support

For technical support questions contact us via mail at: suppo.nosp@m.rt@e.nosp@m.yelog.nosp@m.ic.d.nosp@m.e

EyeLogic GmbH
Altensteinstraße 40
D-14195 Berlin Germany
www: https://www.eyelogic.de
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