Start Gesture Session (Compact 2013)
3/26/2014
When gesture core passes a touch event to the built-in recognizer, if the recognizer state is WaitingForPrimary (no gesture session in progress), GestureRecognizer::RecognizeGesture calls GestureRecognizer::CheckSessionStart to determine whether to start a session. GestureRecognizer::CheckSessionStart examines the incoming touch contacts for a down contact (TOUCHEVENTF_DOWN), which is either primary (TOUCHEVENTF_PRIMARY) or symmetric (TOUCHEVENTF_SYMMETRIC). GestureRecognizer::CheckSessionStart designates the first such contact in the array, if there is one, as the primary candidate, and changes the recognizer state. The state becomes TrackingPrimary if the contact point is a primary, and becomes WaitingForAllUp if the contact point is symmetric.
For information about how gesture core passes a touch event to the recognizers, see Touch Event from Gesture Core to the Recognizers. For information about gesture recognizer states, see Gesture Recognizer States.