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// SPDX-License-Identifier: Unlicense OR MIT
package main
import (
"time"
"gioui.org/f32"
"gioui.org/layout"
"gioui.org/op"
)
const defaultDuration = 300 * time.Millisecond
// Slider implements sliding between old/new widget values.
type Slider struct {
Duration time.Duration
push int
next *op.Ops
nextCall op.CallOp
lastCall op.CallOp
t0 time.Time
offset float32
}
// PushLeft pushes the existing widget to the left.
func (s *Slider) PushLeft() { s.push = 1 }
// PushRight pushes the existing widget to the right.
func (s *Slider) PushRight() { s.push = -1 }
// Layout lays out widget that can be pushed.
func (s *Slider) Layout(gtx layout.Context, w layout.Widget) layout.Dimensions {
if s.push != 0 {
s.next = nil
s.lastCall = s.nextCall
s.offset = float32(s.push)
s.t0 = gtx.Now
s.push = 0
}
var delta time.Duration
if !s.t0.IsZero() {
now := gtx.Now
delta = now.Sub(s.t0)
s.t0 = now
}
if s.offset != 0 {
duration := s.Duration
if duration == 0 {
duration = defaultDuration
}
movement := float32(delta.Seconds()) / float32(duration.Seconds())
if s.offset < 0 {
s.offset += movement
if s.offset >= 0 {
s.offset = 0
}
} else {
s.offset -= movement
if s.offset <= 0 {
s.offset = 0
}
}
op.InvalidateOp{}.Add(gtx.Ops)
}
var dims layout.Dimensions
{
if s.next == nil {
s.next = new(op.Ops)
}
gtx := gtx
gtx.Ops = s.next
gtx.Ops.Reset()
m := op.Record(gtx.Ops)
dims = w(gtx)
s.nextCall = m.Stop()
}
if s.offset == 0 {
s.nextCall.Add(gtx.Ops)
return dims
}
offset := smooth(s.offset)
if s.offset > 0 {
defer op.Offset(f32.Point{
X: float32(dims.Size.X) * (offset - 1),
}).Push(gtx.Ops).Pop()
s.lastCall.Add(gtx.Ops)
defer op.Offset(f32.Point{
X: float32(dims.Size.X),
}).Push(gtx.Ops).Pop()
s.nextCall.Add(gtx.Ops)
} else {
defer op.Offset(f32.Point{
X: float32(dims.Size.X) * (offset + 1),
}).Push(gtx.Ops).Pop()
s.lastCall.Add(gtx.Ops)
defer op.Offset(f32.Point{
X: float32(-dims.Size.X),
}).Push(gtx.Ops).Pop()
s.nextCall.Add(gtx.Ops)
}
return dims
}
// smooth handles -1 to 1 with ease-in-out cubic easing func.
func smooth(t float32) float32 {
if t < 0 {
return -easeInOutCubic(-t)
}
return easeInOutCubic(t)
}
// easeInOutCubic maps a linear value to a ease-in-out-cubic easing function.
func easeInOutCubic(t float32) float32 {
if t < 0.5 {
return 4 * t * t * t
}
return (t-1)*(2*t-2)*(2*t-2) + 1
}