Multi-Touch Functionality; Shadows; Shadow Trick - NEONODE zForce AIR Touch Sensor User Manual

zForce AIR® Touch Sensor User's Guide

4 Multi-Touch Functionality

zForce AIR Touch Sensor determine an object's position by signals derived from emitter-receiver pairs and have the
capacity to detect and track several objects at the same time. Both the HW and the SW have been optimized in
order to support standard touch gestures like, pinch-to-zoom, rotate, swipe and tap. However, some combinations
of two or more objects might need special consideration.

4.1 Shadows

An object directly behind another object cannot be illuminated. In the figure above, object A will not be
detected since illumination is blocked by object B.
The correct receiver must have a clear field of view. Object B is in a region covered only by left looking
receivers. Object B will not be detected because its field of view is blocked by object D.
Object C may be seen by both left and right looking receivers. Although the right looking field of view is
blocked by object D, object C is detected by the left looking receiver.
Object D is detected by both left and right looking receivers.

4.1.1 Shadow Trick

Note that in most cases, user experience is not affected by the shadow situations mentioned above. This is because
of a functionality implemented in the Touch Sensor firmware called "shadow trick", which e.g. generates a smooth
"rotate" feeling despite one touch object being shadowed during the rotate gesture . A previously detected object
that can no longer be detected is still reported as present if:
The object was last seen close to a location where it could be shadowed by another object.
The potentially shadowing object is still detected and hasn't moved away from a shadowing location.
The shadow trick make multi-touch gestures such as "rotate" and "pinch-to-zoom" work better.
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Multi-Touch Functionality
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