shiny/gesture/gesture.go - exp - Git at Google

 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package gesture provides gesture events such as long presses and drags.
 // These are higher level than underlying mouse and touch events.
 package gesture

 import (
 	"fmt"
 	"time"

 	"golang.org/x/exp/shiny/screen"
 	"golang.org/x/mobile/event/mouse"
 )

 // TODO: handle touch events, not just mouse events.
 //
 // TODO: multi-button / multi-touch gestures such as pinch, rotate and tilt?

 const (
 	// TODO: use a resolution-independent unit such as DIPs or Millimetres?
 	dragThreshold = 10 // Pixels.

 	doublePressThreshold = 300 * time.Millisecond
 	longPressThreshold   = 500 * time.Millisecond
 )

 // Type describes the type of a touch event.
 type Type uint8

 const (
 	// TypeStart and TypeEnd are the start and end of a gesture. A gesture
 	// spans multiple events.
 	TypeStart Type = 0
 	TypeEnd   Type = 1

 	// TypeIsXxx is when the gesture is recognized as a long press, double
 	// press or drag. For example, a mouse button press won't generate a
 	// TypeIsLongPress immediately, but if a threshold duration passes without
 	// the corresponding mouse button release, a TypeIsLongPress event is sent.
 	//
 	// Once a TypeIsXxx event is sent, the corresponding Event.Xxx bool field
 	// is set for this and subsequent events. For example, a TypeTap event by
 	// itself doesn't say whether or not it is a single tap or the first tap of
 	// a double tap. If the app needs to distinguish these two sorts of taps,
 	// it can wait until a TypeEnd or TypeIsDoublePress event is seen. If a
 	// TypeEnd is seen before TypeIsDoublePress, or equivalently, if the
 	// TypeEnd event's DoublePress field is false, the gesture is a single tap.
 	//
 	// These attributes aren't exclusive. A long press drag is perfectly valid.
 	//
 	// The uncommon "double press" instead of "double tap" terminology is
 	// because, in this package, taps are associated with button releases, not
 	// button presses. Note also that "double" really means "at least two".
 	TypeIsLongPress   Type = 10
 	TypeIsDoublePress Type = 11
 	TypeIsDrag        Type = 12

 	// TypeTap and TypeDrag are tap and drag events.
 	//
 	// For 'flinging' drags, to simulate inertia, look to the Velocity field of
 	// the TypeEnd event.
 	//
 	// TODO: implement velocity.
 	TypeTap  Type = 20
 	TypeDrag Type = 21

 	// All internal types are >= typeInternal.
 	typeInternal Type = 100

 	// The typeXxxSchedule and typeXxxResolve constants are used for the two
 	// step process for sending an event after a timeout, in a separate
 	// goroutine. There are two steps so that the spawned goroutine is
 	// guaranteed to execute only after any other EventDeque.SendFirst calls
 	// are made for the one underlying mouse or touch event.

 	typeDoublePressSchedule Type = 100
 	typeDoublePressResolve  Type = 101

 	typeLongPressSchedule Type = 110
 	typeLongPressResolve  Type = 111
 )

 func (t Type) String() string {
 	switch t {
 	case TypeStart:
 		return "Start"
 	case TypeEnd:
 		return "End"
 	case TypeIsLongPress:
 		return "IsLongPress"
 	case TypeIsDoublePress:
 		return "IsDoublePress"
 	case TypeIsDrag:
 		return "IsDrag"
 	case TypeTap:
 		return "Tap"
 	case TypeDrag:
 		return "Drag"
 	default:
 		return fmt.Sprintf("gesture.Type(%d)", t)
 	}
 }

 // Point is a mouse or touch location, in pixels.
 type Point struct {
 	X, Y float32
 }

 // Event is a gesture event.
 type Event struct {
 	// Type is the gesture type.
 	Type Type

 	// Drag, LongPress and DoublePress are set when the gesture is recognized as
 	// a drag, etc.
 	//
 	// Note that these status fields can be lost during a gesture's events over
 	// time: LongPress can be set for the first press of a double press, but
 	// unset on the second press.
 	Drag        bool
 	LongPress   bool
 	DoublePress bool

 	// InitialPos is the initial position of the button press or touch that
 	// started this gesture.
 	InitialPos Point

 	// CurrentPos is the current position of the button or touch event.
 	CurrentPos Point

 	// TODO: a "Velocity Point" field. See
 	//	- frameworks/native/libs/input/VelocityTracker.cpp in AOSP, or
 	//	- https://chromium.googlesource.com/chromium/src/+/master/ui/events/gesture_detection/velocity_tracker.cc in Chromium,
 	// for some velocity tracking implementations.

 	// Time is the event's time.
 	Time time.Time

 	// TODO: include the mouse Button and key Modifiers?
 }

 type internalEvent struct {
 	eventFilter *EventFilter

 	typ  Type
 	x, y float32

 	// pressCounter is the EventFilter.pressCounter value at the time this
 	// internal event was scheduled to be delivered after a timeout. It detects
 	// whether there have been other button presses and releases during that
 	// timeout, and hence whether this internalEvent is obsolete.
 	pressCounter uint32
 }

 // EventFilter generates gesture events from lower level mouse and touch
 // events.
 type EventFilter struct {
 	EventDeque screen.EventDeque

 	inProgress  bool
 	drag        bool
 	longPress   bool
 	doublePress bool

 	// initialPos is the initial position of the button press or touch that
 	// started this gesture.
 	initialPos Point

 	// pressButton is the initial button that started this gesture. If
 	// button.None, no gesture is in progress.
 	pressButton mouse.Button

 	// pressCounter is incremented on every button press and release.
 	pressCounter uint32
 }

 func (f *EventFilter) sendFirst(t Type, x, y float32, now time.Time) {
 	if t >= typeInternal {
 		f.EventDeque.SendFirst(internalEvent{
 			eventFilter:  f,
 			typ:          t,
 			x:            x,
 			y:            y,
 			pressCounter: f.pressCounter,
 		})
 		return
 	}
 	f.EventDeque.SendFirst(Event{
 		Type:        t,
 		Drag:        f.drag,
 		LongPress:   f.longPress,
 		DoublePress: f.doublePress,
 		InitialPos:  f.initialPos,
 		CurrentPos: Point{
 			X: x,
 			Y: y,
 		},
 		// TODO: Velocity.
 		Time: now,
 	})
 }

 func (f *EventFilter) sendAfter(e internalEvent, sleep time.Duration) {
 	time.Sleep(sleep)
 	f.EventDeque.SendFirst(e)
 }

 func (f *EventFilter) end(x, y float32, now time.Time) {
 	f.sendFirst(TypeEnd, x, y, now)
 	f.inProgress = false
 	f.drag = false
 	f.longPress = false
 	f.doublePress = false
 	f.initialPos = Point{}
 	f.pressButton = mouse.ButtonNone
 }

 // Filter filters the event. It can return e, a different event, or nil to
 // consume the event. It can also trigger side effects such as pushing new
 // events onto its EventDeque.
 func (f *EventFilter) Filter(e interface{}) interface{} {
 	switch e := e.(type) {
 	case internalEvent:
 		if e.eventFilter != f {
 			break
 		}

 		now := time.Now()

 		switch e.typ {
 		case typeDoublePressSchedule:
 			e.typ = typeDoublePressResolve
 			go f.sendAfter(e, doublePressThreshold)

 		case typeDoublePressResolve:
 			if e.pressCounter == f.pressCounter {
 				// It's a single press only.
 				f.end(e.x, e.y, now)
 			}

 		case typeLongPressSchedule:
 			e.typ = typeLongPressResolve
 			go f.sendAfter(e, longPressThreshold)

 		case typeLongPressResolve:
 			if e.pressCounter == f.pressCounter && !f.drag {
 				f.longPress = true
 				f.sendFirst(TypeIsLongPress, e.x, e.y, now)
 			}
 		}
 		return nil

 	case mouse.Event:
 		now := time.Now()

 		switch e.Direction {
 		case mouse.DirNone:
 			if f.pressButton == mouse.ButtonNone {
 				break
 			}
 			startDrag := false
 			if !f.drag &&
 				(abs(e.X-f.initialPos.X) > dragThreshold || abs(e.Y-f.initialPos.Y) > dragThreshold) {
 				f.drag = true
 				startDrag = true
 			}
 			if f.drag {
 				f.sendFirst(TypeDrag, e.X, e.Y, now)
 			}
 			if startDrag {
 				f.sendFirst(TypeIsDrag, e.X, e.Y, now)
 			}

 		case mouse.DirPress:
 			if f.pressButton != mouse.ButtonNone {
 				break
 			}

 			oldInProgress := f.inProgress
 			oldDoublePress := f.doublePress

 			f.drag = false
 			f.longPress = false
 			f.doublePress = f.inProgress
 			f.initialPos = Point{e.X, e.Y}
 			f.pressButton = e.Button
 			f.pressCounter++

 			f.inProgress = true

 			f.sendFirst(typeLongPressSchedule, e.X, e.Y, now)
 			if !oldDoublePress && f.doublePress {
 				f.sendFirst(TypeIsDoublePress, e.X, e.Y, now)
 			}
 			if !oldInProgress {
 				f.sendFirst(TypeStart, e.X, e.Y, now)
 			}

 		case mouse.DirRelease:
 			if f.pressButton != e.Button {
 				break
 			}
 			f.pressButton = mouse.ButtonNone
 			f.pressCounter++

 			if f.drag {
 				f.end(e.X, e.Y, now)
 				break
 			}
 			f.sendFirst(typeDoublePressSchedule, e.X, e.Y, now)
 			f.sendFirst(TypeTap, e.X, e.Y, now)
 		}
 	}
 	return e
 }

 func abs(x float32) float32 {
 	if x < 0 {
 		return -x
 	} else if x == 0 {
 		return 0 // Handle floating point negative zero.
 	}
 	return x
 }
	// Copyright 2016 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package gesture provides gesture events such as long presses and drags.
	// These are higher level than underlying mouse and touch events.
	package gesture

	import (
	"fmt"
	"time"

	"golang.org/x/exp/shiny/screen"
	"golang.org/x/mobile/event/mouse"
	)

	// TODO: handle touch events, not just mouse events.
	//
	// TODO: multi-button / multi-touch gestures such as pinch, rotate and tilt?

	const (
	// TODO: use a resolution-independent unit such as DIPs or Millimetres?
	dragThreshold = 10 // Pixels.

	doublePressThreshold = 300 * time.Millisecond
	longPressThreshold = 500 * time.Millisecond
	)

	// Type describes the type of a touch event.
	type Type uint8

	const (
	// TypeStart and TypeEnd are the start and end of a gesture. A gesture
	// spans multiple events.
	TypeStart Type = 0
	TypeEnd Type = 1

	// TypeIsXxx is when the gesture is recognized as a long press, double
	// press or drag. For example, a mouse button press won't generate a
	// TypeIsLongPress immediately, but if a threshold duration passes without
	// the corresponding mouse button release, a TypeIsLongPress event is sent.
	//
	// Once a TypeIsXxx event is sent, the corresponding Event.Xxx bool field
	// is set for this and subsequent events. For example, a TypeTap event by
	// itself doesn't say whether or not it is a single tap or the first tap of
	// a double tap. If the app needs to distinguish these two sorts of taps,
	// it can wait until a TypeEnd or TypeIsDoublePress event is seen. If a
	// TypeEnd is seen before TypeIsDoublePress, or equivalently, if the
	// TypeEnd event's DoublePress field is false, the gesture is a single tap.
	//
	// These attributes aren't exclusive. A long press drag is perfectly valid.
	//
	// The uncommon "double press" instead of "double tap" terminology is
	// because, in this package, taps are associated with button releases, not
	// button presses. Note also that "double" really means "at least two".
	TypeIsLongPress Type = 10
	TypeIsDoublePress Type = 11
	TypeIsDrag Type = 12

	// TypeTap and TypeDrag are tap and drag events.
	//
	// For 'flinging' drags, to simulate inertia, look to the Velocity field of
	// the TypeEnd event.
	//
	// TODO: implement velocity.
	TypeTap Type = 20
	TypeDrag Type = 21

	// All internal types are >= typeInternal.
	typeInternal Type = 100

	// The typeXxxSchedule and typeXxxResolve constants are used for the two
	// step process for sending an event after a timeout, in a separate
	// goroutine. There are two steps so that the spawned goroutine is
	// guaranteed to execute only after any other EventDeque.SendFirst calls
	// are made for the one underlying mouse or touch event.

	typeDoublePressSchedule Type = 100
	typeDoublePressResolve Type = 101

	typeLongPressSchedule Type = 110
	typeLongPressResolve Type = 111
	)

	func (t Type) String() string {
	switch t {
	case TypeStart:
	return "Start"
	case TypeEnd:
	return "End"
	case TypeIsLongPress:
	return "IsLongPress"
	case TypeIsDoublePress:
	return "IsDoublePress"
	case TypeIsDrag:
	return "IsDrag"
	case TypeTap:
	return "Tap"
	case TypeDrag:
	return "Drag"
	default:
	return fmt.Sprintf("gesture.Type(%d)", t)
	}
	}

	// Point is a mouse or touch location, in pixels.
	type Point struct {
	X, Y float32
	}

	// Event is a gesture event.
	type Event struct {
	// Type is the gesture type.
	Type Type

	// Drag, LongPress and DoublePress are set when the gesture is recognized as
	// a drag, etc.
	//
	// Note that these status fields can be lost during a gesture's events over
	// time: LongPress can be set for the first press of a double press, but
	// unset on the second press.
	Drag bool
	LongPress bool
	DoublePress bool

	// InitialPos is the initial position of the button press or touch that
	// started this gesture.
	InitialPos Point

	// CurrentPos is the current position of the button or touch event.
	CurrentPos Point

	// TODO: a "Velocity Point" field. See
	// - frameworks/native/libs/input/VelocityTracker.cpp in AOSP, or
	// - https://chromium.googlesource.com/chromium/src/+/master/ui/events/gesture_detection/velocity_tracker.cc in Chromium,
	// for some velocity tracking implementations.

	// Time is the event's time.
	Time time.Time

	// TODO: include the mouse Button and key Modifiers?
	}

	type internalEvent struct {
	eventFilter *EventFilter

	typ Type
	x, y float32

	// pressCounter is the EventFilter.pressCounter value at the time this
	// internal event was scheduled to be delivered after a timeout. It detects
	// whether there have been other button presses and releases during that
	// timeout, and hence whether this internalEvent is obsolete.
	pressCounter uint32
	}

	// EventFilter generates gesture events from lower level mouse and touch
	// events.
	type EventFilter struct {
	EventDeque screen.EventDeque

	inProgress bool
	drag bool
	longPress bool
	doublePress bool

	// initialPos is the initial position of the button press or touch that
	// started this gesture.
	initialPos Point

	// pressButton is the initial button that started this gesture. If
	// button.None, no gesture is in progress.
	pressButton mouse.Button

	// pressCounter is incremented on every button press and release.
	pressCounter uint32
	}

	func (f *EventFilter) sendFirst(t Type, x, y float32, now time.Time) {
	if t >= typeInternal {
	f.EventDeque.SendFirst(internalEvent{
	eventFilter: f,
	typ: t,
	x: x,
	y: y,
	pressCounter: f.pressCounter,
	})
	return
	}
	f.EventDeque.SendFirst(Event{
	Type: t,
	Drag: f.drag,
	LongPress: f.longPress,
	DoublePress: f.doublePress,
	InitialPos: f.initialPos,
	CurrentPos: Point{
	X: x,
	Y: y,
	},
	// TODO: Velocity.
	Time: now,
	})
	}

	func (f *EventFilter) sendAfter(e internalEvent, sleep time.Duration) {
	time.Sleep(sleep)
	f.EventDeque.SendFirst(e)
	}

	func (f *EventFilter) end(x, y float32, now time.Time) {
	f.sendFirst(TypeEnd, x, y, now)
	f.inProgress = false
	f.drag = false
	f.longPress = false
	f.doublePress = false
	f.initialPos = Point{}
	f.pressButton = mouse.ButtonNone
	}

	// Filter filters the event. It can return e, a different event, or nil to
	// consume the event. It can also trigger side effects such as pushing new
	// events onto its EventDeque.
	func (f *EventFilter) Filter(e interface{}) interface{} {
	switch e := e.(type) {
	case internalEvent:
	if e.eventFilter != f {
	break
	}

	now := time.Now()

	switch e.typ {
	case typeDoublePressSchedule:
	e.typ = typeDoublePressResolve
	go f.sendAfter(e, doublePressThreshold)

	case typeDoublePressResolve:
	if e.pressCounter == f.pressCounter {
	// It's a single press only.
	f.end(e.x, e.y, now)
	}

	case typeLongPressSchedule:
	e.typ = typeLongPressResolve
	go f.sendAfter(e, longPressThreshold)

	case typeLongPressResolve:
	if e.pressCounter == f.pressCounter && !f.drag {
	f.longPress = true
	f.sendFirst(TypeIsLongPress, e.x, e.y, now)
	}
	}
	return nil

	case mouse.Event:
	now := time.Now()

	switch e.Direction {
	case mouse.DirNone:
	if f.pressButton == mouse.ButtonNone {
	break
	}
	startDrag := false
	if !f.drag &&
	(abs(e.X-f.initialPos.X) > dragThreshold \|\| abs(e.Y-f.initialPos.Y) > dragThreshold) {
	f.drag = true
	startDrag = true
	}
	if f.drag {
	f.sendFirst(TypeDrag, e.X, e.Y, now)
	}
	if startDrag {
	f.sendFirst(TypeIsDrag, e.X, e.Y, now)
	}

	case mouse.DirPress:
	if f.pressButton != mouse.ButtonNone {
	break
	}

	oldInProgress := f.inProgress
	oldDoublePress := f.doublePress

	f.drag = false
	f.longPress = false
	f.doublePress = f.inProgress
	f.initialPos = Point{e.X, e.Y}
	f.pressButton = e.Button
	f.pressCounter++

	f.inProgress = true

	f.sendFirst(typeLongPressSchedule, e.X, e.Y, now)
	if !oldDoublePress && f.doublePress {
	f.sendFirst(TypeIsDoublePress, e.X, e.Y, now)
	}
	if !oldInProgress {
	f.sendFirst(TypeStart, e.X, e.Y, now)
	}

	case mouse.DirRelease:
	if f.pressButton != e.Button {
	break
	}
	f.pressButton = mouse.ButtonNone
	f.pressCounter++

	if f.drag {
	f.end(e.X, e.Y, now)
	break
	}
	f.sendFirst(typeDoublePressSchedule, e.X, e.Y, now)
	f.sendFirst(TypeTap, e.X, e.Y, now)
	}
	}
	return e
	}

	func abs(x float32) float32 {
	if x < 0 {
	return -x
	} else if x == 0 {
	return 0 // Handle floating point negative zero.
	}
	return x
	}