gio/widget/material/loader.go

// SPDX-License-Identifier: Unlicense OR MIT

package material

import (
	"image"
	"image/color"
	"math"
	"time"

	"gioui.org/f32"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
)

type LoaderStyle struct {
	Color color.NRGBA
}

func Loader(th *Theme) LoaderStyle {
	return LoaderStyle{
		Color: th.Palette.ContrastBg,
	}
}

func (l LoaderStyle) Layout(gtx layout.Context) layout.Dimensions {
	diam := gtx.Constraints.Min.X
	if minY := gtx.Constraints.Min.Y; minY > diam {
		diam = minY
	}
	if diam == 0 {
		diam = gtx.Dp(24)
	}
	sz := gtx.Constraints.Constrain(image.Pt(diam, diam))
	radius := sz.X / 2
	defer op.Offset(image.Pt(radius, radius)).Push(gtx.Ops).Pop()

	dt := float32((time.Duration(gtx.Now.UnixNano()) % (time.Second)).Seconds())
	startAngle := dt * math.Pi * 2
	endAngle := startAngle + math.Pi*1.5

	defer clipLoader(gtx.Ops, startAngle, endAngle, float32(radius)).Push(gtx.Ops).Pop()
	paint.ColorOp{
		Color: l.Color,
	}.Add(gtx.Ops)
	defer op.Offset(image.Pt(-radius, -radius)).Push(gtx.Ops).Pop()
	paint.PaintOp{}.Add(gtx.Ops)
	gtx.Execute(op.InvalidateCmd{})
	return layout.Dimensions{
		Size: sz,
	}
}

func clipLoader(ops *op.Ops, startAngle, endAngle, radius float32) clip.Op {
	const thickness = .25

	var (
		width = radius * thickness
		delta = endAngle - startAngle

		vy, vx = math.Sincos(float64(startAngle))

		inner  = radius * (1. - thickness*.5)
		pen    = f32.Pt(float32(vx), float32(vy)).Mul(inner)
		center = f32.Pt(0, 0).Sub(pen)

		p clip.Path
	)

	p.Begin(ops)
	p.Move(pen)
	p.Arc(center, center, delta)
	return clip.Stroke{
		Path:  p.End(),
		Width: width,
	}.Op()
}