gio/widget/material/progressbar.go

// SPDX-License-Identifier: Unlicense OR MIT

package material

import (
	"image"
	"image/color"

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

type ProgressBarStyle struct {
	Color color.RGBA
}

func ProgressBar(th *Theme) ProgressBarStyle {
	return ProgressBarStyle{
		Color: th.Color.Primary,
	}
}

func (b ProgressBarStyle) Layout(gtx *layout.Context, progress int) {
	shader := func(width float32, color color.RGBA) {
		maxHeight := unit.Dp(4)
		rr := float32(gtx.Px(unit.Dp(2)))

		d := image.Point{X: int(width), Y: gtx.Px(maxHeight)}
		dr := f32.Rectangle{
			Max: f32.Point{X: float32(d.X), Y: float32(d.Y)},
		}

		clip.Rect{
			Rect: f32.Rectangle{Max: f32.Point{X: width, Y: float32(gtx.Px(maxHeight))}},
			NE:   rr, NW: rr, SE: rr, SW: rr,
		}.Op(gtx.Ops).Add(gtx.Ops)

		paint.ColorOp{Color: color}.Add(gtx.Ops)
		paint.PaintOp{Rect: dr}.Add(gtx.Ops)

		gtx.Dimensions = layout.Dimensions{Size: d}
	}

	if progress > 100 {
		progress = 100
	} else if progress < 0 {
		progress = 0
	}

	progressBarWidth := float32(gtx.Constraints.Max.X)

	layout.Stack{Alignment: layout.W}.Layout(gtx,
		layout.Stacked(func() {
			// Use a transparent equivalent of progress color.
			bgCol := mulAlpha(b.Color, 150)

			shader(progressBarWidth, bgCol)
		}),
		layout.Stacked(func() {
			fillWidth := (progressBarWidth / 100) * float32(progress)
			shader(fillWidth, b.Color)
		}),
	)
}

// mulAlpha scales all color components by alpha/255.
func mulAlpha(c color.RGBA, alpha uint8) color.RGBA {
	a := uint16(alpha)
	return color.RGBA{
		A: uint8(uint16(c.A) * a / 255),
		R: uint8(uint16(c.R) * a / 255),
		G: uint8(uint16(c.G) * a / 255),
		B: uint8(uint16(c.B) * a / 255),
	}
}