QT application development

Some multi-touch applications use a cross platform development tool called QT and use the QTouchEvents interface to receive system-level touches. Unfortunately the standard way Qt determines the screen location of the touches in Mac OS X is incompatible with UPDDGestures: Qt assumes that the touches are coming from a trackpad since all system touches are assumed to originate from a trackpad. In that case, Qt has the touch start at the mouse cursor location (which is not what is needed in a touch screen environment), and the touch's movement speed is calculated using the physical dimensions of the trackpad. However, it won't get any dimensions since no trackpad is present. Instead, it calculates that the trackpad has a width and height of 0, and consequently the touches won't move anywhere.

For touch-enabled Qt applications to work with UPDDGestures they must use the normalized position of the touches, not the screen position. Sadly, we suspect most Qt apps use a touch's screen position.

One such popular multi-touch enabled application is Snowflake from NUITEQ. The developers of Snowflake are working on changing the interface to utilize the normalized position but until this change is made you will need to use our UPDD TUIO server to utilize Snowflake’s TUIO interface. This has been tested and works well but it does mean that the gesture software cannot be used at the same time as the TUIO interface as it causes a phantom touch in Snowflake.