ofxMultitouch

openFrameworks is an open source toolkit for creative coding.

Introduction

ofxMultitouch is an openFrameworks that enables multitouch for multi-touch monitors and touch screen overlays on Windows and Linux. On Windows 7, 8, and 10, the package intercepts and responds to Windows messages for touch and mouse events. On Linux it uses libinput, and has only been tested on Linux Mint / Ubuntu.

Installation

ofMultitouch is made from a fork of Trent Brooks' ofxWinTouchHook.

• On Windows, there are no dependencies to be installed
• On Linux, install libinput: sudo apt-get install libinput-dev

Installing ofxMultitouch:

• Download from GitHub
• Unzip the folder and rename it from ofxMultitouch-master to ofxMultitouch
• Place it in your openFrameworks/addons folder.
• You can also clone the repo directly into your addons directory: cd <OF>/addons and then git clone <repository URL>

Running examples:

• Import the example into the project generator
• Create a new project
• Open the project file in your IDE
• On Linux, examples must be run as root, e.g. sudo example-touchCircles. The RunDebug and RunRelease targets for the example files have been modified to do this automatically, but you will need to enter the root password when you run them.

(Windows version made and tested on Windows 10, openFrameworks 9.8 and 10.1, and Visual Studio 2017 - feel free to reach out if you run into problems in other environments) Linux version made and tested on Linux Mint, openFrameworks 12

Examples

touchCircles

• Displays circles under each active touch.
• A simple example to make sure current install & hardware are working properly.

touchDraw

• Touch and drag the screen to produce a randomly colored line displaying the path of your fingertip. Can support at least 10 touches at once (though this number may change based on hardware).
• Use the mouse to pan.
• Press 0 to reset panning.
• Press SPACE to clear canvas.

imageGestures

• Use two fingers to pan and zoom an image.
• Image is confined to screen space and cannot be translated past the edges.
• Press SPACE to reset transformations.

How does it work?

ofxMultitouch runs by watching Windows Messages, which can be read about at the Microsoft Docs.

Hooks

"A hook is a mechanism by which an application can intercept events, such as messages, mouse actions, and keystrokes. A function that intercepts a particular type of event is known as a hook procedure. A hook procedure can act on each event it receives, and then modify or discard the event."

The specific messages we look at include:

• mouse messages WM_LBUTTONDOWN and WM_LBUTTONUP
• touch messages WM_POINTERDOWN, WM_POINTERUPDATE, and WM_POINTERUP

These touch messages control most of our touch functionality⁠—as you might expect, they correspond to touchDown-, touchMoved-, and touchUp-style functions, respectively.

A Single Touch

However, Windows typically treats a single touch event as a mouse event. This allows a touch screen user to interact with programs as expected: dragging windows, clicking buttons, etc. Unfortunately, this means a single touch creates both touch and mouse messages. This can get confusing for us!

For example, we use the mouse to pan in example-touchDraw. A single touch would end up calling the touch messages we use to draw, but it would also call the mouse messages we use to pan. This ends up with some pretty uncomfortable functionality; so, we use a hook to intercept our WM_LBUTTONDOWN/WM_LBUTTONUP messages, check a flag to see if they originated from a touch, and pass on an event to help us differentiate a moving touch from a mouse drag.