Decay mobile scroll as users expect on a touch display

internal/driver/mobile/canvas.go

@@ -25,6 +25,7 @@ type canvas struct {
  initialized bool
  lastTapDown map[int]time.Time
  lastTapDownPos map[int]fyne.Position
+ lastTapDelta map[int]fyne.Delta
  menu fyne.CanvasObject
  padded bool
  scale float32
@@ -54,6 +55,7 @@ func newCanvas(dev fyne.Device) fyne.Canvas {
  device: d,
  lastTapDown: make(map[int]time.Time),
  lastTapDownPos: make(map[int]fyne.Position),
+ lastTapDelta: make(map[int]fyne.Delta),
  padded: true,
  scale: dev.SystemScaleForWindow(nil), // we don't need a window parameter on mobile,
  touched: make(map[int]mobile.Touchable),
@@ -258,6 +260,8 @@ func (c *canvas) tapMove(pos fyne.Position, tapID int,
  return
  }
  c.lastTapDownPos[tapID] = pos
+ offset := fyne.Delta{DX: deltaX, DY: deltaY}
+ c.lastTapDelta[tapID] = offset
 
  co, objPos, _ := c.findObjectAtPositionMatching(pos, func(object fyne.CanvasObject) bool {
  if _, ok := object.(fyne.Draggable); ok {
@@ -292,7 +296,7 @@ func (c *canvas) tapMove(pos fyne.Position, tapID int,
  ev := &fyne.DragEvent{}
  draggedObjDelta := c.dragStart.Subtract(c.dragging.(fyne.CanvasObject).Position())
  ev.Position = pos.Subtract(c.dragOffset).Add(draggedObjDelta)
- ev.Dragged = fyne.Delta{DX: deltaX, DY: deltaY}
+ ev.Dragged = offset
 
  dragCallback(c.dragging, ev)
 }
@@ -301,10 +305,11 @@ func (c *canvas) tapUp(pos fyne.Position, tapID int,
  tapCallback func(fyne.Tappable, *fyne.PointEvent),
  tapAltCallback func(fyne.SecondaryTappable, *fyne.PointEvent),
  doubleTapCallback func(fyne.DoubleTappable, *fyne.PointEvent),
- dragCallback func(fyne.Draggable)) {
+ dragCallback func(fyne.Draggable, *fyne.DragEvent)) {
 
  if c.dragging != nil {
- dragCallback(c.dragging)
+ previousDelta := c.lastTapDelta[tapID]
+ dragCallback(c.dragging, &fyne.DragEvent{Dragged: previousDelta})
 
  c.dragging = nil
  return

internal/driver/mobile/canvas_test.go

@@ -249,7 +249,7 @@ func Test_canvas_Tappable(t *testing.T) {
  c.tapUp(fyne.NewPos(15, 15), 0, func(wid fyne.Tappable, ev *fyne.PointEvent) {
  }, func(wid fyne.SecondaryTappable, ev *fyne.PointEvent) {
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
- }, func(wid fyne.Draggable) {
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
  })
  assert.True(t, content.up)
 
@@ -286,7 +286,7 @@ func Test_canvas_Tapped(t *testing.T) {
  wid.TappedSecondary(ev)
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
  wid.DoubleTapped(ev)
- }, func(wid fyne.Draggable) {
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
  })
 
  assert.True(t, tapped, "tap primary")
@@ -340,7 +340,7 @@ func Test_canvas_TappedMulti(t *testing.T) {
  }, func(wid fyne.SecondaryTappable, ev *fyne.PointEvent) {
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
  wid.DoubleTapped(ev)
- }, func(wid fyne.Draggable) {
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
  })
 
  assert.False(t, buttonTap, "button should not be tapped")
@@ -369,7 +369,7 @@ func Test_canvas_TappedSecondary(t *testing.T) {
  wid.TappedSecondary(ev)
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
  wid.DoubleTapped(ev)
- }, func(wid fyne.Draggable) {
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
  })
 
  assert.False(t, obj.tap, "don't tap primary")
@@ -464,7 +464,7 @@ func simulateTap(c *canvas) {
  }, func(wid fyne.SecondaryTappable, ev *fyne.PointEvent) {
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
  wid.DoubleTapped(ev)
- }, func(wid fyne.Draggable) {
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
  })
 }
 

internal/driver/mobile/device_android.go

@@ -4,7 +4,7 @@ package mobile
 
 import "fyne.io/fyne/v2"
 
-const tapYOffset = -12.0 // to compensate for how we hold our fingers on the device
+const tapYOffset = -8.0 // to compensate for how we hold our fingers on the device
 
 func (*device) SystemScaleForWindow(_ fyne.Window) float32 {
  if currentDPI >= 600 {

internal/driver/mobile/device_ios.go

@@ -4,7 +4,7 @@ package mobile
 
 import "fyne.io/fyne/v2"
 
-const tapYOffset = -12.0 // to compensate for how we hold our fingers on the device
+const tapYOffset = -8.0 // to compensate for how we hold our fingers on the device
 
 func (*device) SystemScaleForWindow(_ fyne.Window) float32 {
  if currentDPI >= 450 {

internal/driver/mobile/driver.go

@@ -1,6 +1,7 @@
 package mobile
 
 import (
+ "math"
  "runtime"
  "strconv"
  "sync/atomic"
@@ -30,9 +31,11 @@ import (
 )
 
 const (
- tapMoveThreshold = 4.0 // how far can we move before it is a drag
- tapSecondaryDelay = 300 * time.Millisecond // how long before secondary tap
- tapDoubleDelay = 500 * time.Millisecond // max duration between taps for a DoubleTap event
+ tapMoveDecay = 0.92 // how much should the scroll continue decay on each frame?
+ tapMoveEndThreshold = 2.0 // at what offset will we stop decaying?
+ tapMoveThreshold = 4.0 // how far can we move before it is a drag
+ tapSecondaryDelay = 300 * time.Millisecond // how long before secondary tap
+ tapDoubleDelay = 500 * time.Millisecond // max duration between taps for a DoubleTap event
 )
 
 // Configuration is the system information about the current device
@@ -399,8 +402,27 @@ func (d *driver) tapUpCanvas(w *window, x, y float32, tapID touch.Sequence) {
  w.QueueEvent(func() { wid.TappedSecondary(ev) })
  }, func(wid fyne.DoubleTappable, ev *fyne.PointEvent) {
  w.QueueEvent(func() { wid.DoubleTapped(ev) })
- }, func(wid fyne.Draggable) {
- w.QueueEvent(wid.DragEnd)
+ }, func(wid fyne.Draggable, ev *fyne.DragEvent) {
+ if math.Abs(float64(ev.Dragged.DX)) <= tapMoveEndThreshold && math.Abs(float64(ev.Dragged.DY)) <= tapMoveEndThreshold {
+ w.QueueEvent(wid.DragEnd)
+ return
+ }
+
+ go func() {
+ for math.Abs(float64(ev.Dragged.DX)) > tapMoveEndThreshold || math.Abs(float64(ev.Dragged.DY)) > tapMoveEndThreshold {
+ if math.Abs(float64(ev.Dragged.DX)) > 0 {
+ ev.Dragged.DX *= tapMoveDecay
+ }
+ if math.Abs(float64(ev.Dragged.DY)) > 0 {
+ ev.Dragged.DY *= tapMoveDecay
+ }
+
+ w.QueueEvent(func() { wid.Dragged(ev) })
+ time.Sleep(time.Millisecond * 16)
+ }
+
+ w.QueueEvent(wid.DragEnd)
+ }()
  })
 }