Touch events

These events are used to track multipoint touches. Single touches emulate mouse events.If you do not need to track multi-point touches, then it is easier to use mouse events

Event	Constant	Description
"touch-start"	TouchStart	The surface touched.
"touch-end"	TouchEnd	Surface touch completed.
"touch-move"	TouchMove	One or more touches changed position
"touch-cancel"	TouchCancel	The touch is interrupted.

The main event data listener has the following format:


func(View, TouchEvent)

where the second argument describes the touch parameters. The TouchEvent structure has the following fields:

Field	Type	Description
TimeStamp	uint64	The time the event was created (in milliseconds). The starting point depends on the browser implementation (EPOCH, browser launch, etc.).
Touches	[]Touch	Array of Touch structures, each describing one touch
CtrlKey	bool	The Ctrl key was active when the event occurred.
ShiftKey	bool	The Shift key was active when the event occurred.
AltKey	bool	The Alt (Option or ⌥ in OS X) key was active when the event occurred.
MetaKey	bool	The Meta key (for Mac, this is the ⌘ Command key; for Windows, the Windows key ⊞) was active when the event occurred.

The Touch structure describes a single touch and has the following fields

Field	Type	Description
Identifier	int	A unique identifier assigned to each touch and does not change until it is completed.
X	float64	The horizontal position of the mouse relative to the origin View
Y	float64	The vertical position of the mouse relative to the origin View
ClientX	float64	Horizontal position of the mouse relative to the upper left corner of the application
ClientY	float64	The vertical position of the mouse relative to the upper left corner of the application
ScreenX	float64	Horizontal position of the mouse relative to the upper left corner of the screen
ScreenY	float64	Vertical position of the mouse relative to the upper left corner of the screen
RadiusX	float64	The x-radius of the ellipse, in pixels, that most closely delimits the area of contact with the screen.
RadiusY	float64	The y-radius of the ellipse, in pixels, that most closely delimits the area of contact with the screen.
RotationAngle	float64	The angle (in degrees) to rotate the ellipse clockwise, described by the radiusX and radiusY parameters, to best cover the contact area between the user and the surface.
Force	float64	The amount of pressure from 0.0 (no pressure) to 1.0 (maximum pressure) that the user applies to the surface.

You can also use listeners in the following formats:

func(TouchEvent)
func(View)
func()

You can get lists of listeners for touch events using the functions:

func GetTouchStartListeners(view View, subviewID ...string) []func(View, TouchEvent)
func GetTouchEndListeners(view View, subviewID ...string) []func(View, TouchEvent)
func GetTouchMoveListeners(view View, subviewID ...string) []func(View, TouchEvent)
func GetTouchCancelListeners(view View, subviewID ...string) []func(View, TouchEvent)