Edge detection algorithm for Windows 8 touchpads

Updated: October 12, 2012

This topic describes the edge detection algorithm for Windows 8 touchpads.

This information applies to the following operating system:

  • Windows 8

A swipe from the sensor edge must meet a set of conditions for the touchpad to interpret the swipe as a successful swipe in from the edges.

The following diagram shows the parameters that the touchpad uses in its algorithm for detecting and interpreting a swipe gesture.

Edge detection algorithm

VariableDescriptionRecommendations
W Width of disambiguation region max. 5mm
R Decision radius max. 10mm
αT Top success angle max. 50°
αBBottom success angle max. 50°

 

A successful swipe should start within the width of the disambiguation region (W), and the swipe action should travel more than the decision radius (R) between the top and bottom success angle (αT, αB). As soon as contact travels more than the width threshold, the corresponding keyboard shortcut should be issued. As long as the finger still contacts the touchpad surface, further contact movement should not cause another cursor movement or other shortcut actions (gestures). Re-entrance of contact into the disambiguation region should not trigger new edge shortcut actions.

Widening the disambiguation region (W) at the edge of the device makes it easier for the user to find the edge, but it reduces the useful area of the touchpad surface. Increasing the decision radius increases the accuracy of gesture detection, but can slow down the edge detections. For a consistent experience, a device should not exceed the recommended parameters in its edge detection algorithm.

The single-finger swipe gestures are not recommended for a touchpad that is significantly smaller than the minimum recommended size (90mm (w) x 55mm (h)). To avoid confusion and conflicts in usability features, do not assign alternative gestures to engage the Microsoft Windows shortcut keys.

Related topics

Design recommendations for Windows 8 touchpads

 

 

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