3 files changed, 119 insertions(+), 0 deletions(-)

A gio-extras/scroll/main.go
M go.mod
M go.sum

@@ 0,0 1,116 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+package main
+
+// A simple Gio program. See https://gioui.org for more information.
+
+import (
+	"log"
+	"os"
+	"strconv"
+
+	"gioui.org/app"
+	"gioui.org/io/system"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/unit"
+	"gioui.org/widget"
+	"gioui.org/widget/material"
+	"git.sr.ht/~whereswaldon/scroll"
+
+	"gioui.org/font/gofont"
+)
+
+func main() {
+	go func() {
+		w := app.NewWindow()
+		if err := loop(w); err != nil {
+			log.Fatal(err)
+		}
+		os.Exit(0)
+	}()
+	app.Main()
+}
+
+var (
+	increaseBtn, decreaseBtn widget.Clickable
+	length                   int
+	list                     layout.List
+
+	indicator scroll.Scrollable
+)
+
+type (
+	C = layout.Context
+	D = layout.Dimensions
+)
+
+func loop(w *app.Window) error {
+	th := material.NewTheme(gofont.Collection())
+	var ops op.Ops
+	length = 32
+	list.Axis = layout.Vertical
+	list.Alignment = layout.Middle
+	inset := layout.UniformInset(unit.Dp(4))
+	for {
+		e := <-w.Events()
+		switch e := e.(type) {
+		case system.DestroyEvent:
+			return e.Err
+		case system.FrameEvent:
+			gtx := layout.NewContext(&ops, e)
+			if increaseBtn.Clicked() {
+				length *= 2
+			}
+			if decreaseBtn.Clicked() {
+				length /= 2
+				if length < 1 {
+					length = 1
+				}
+			}
+			/*
+				Here we check whether the scrollbar experienced user-initiated scrolling
+				during the past frame and update the state of the List accordingly
+			*/
+			if scrolled, progress := indicator.Scrolled(); scrolled {
+				list.Position.First = int(float32(length) * progress)
+			}
+			const third float32 = 1.0 / 3.0
+			layout.Flex{Axis: layout.Vertical}.Layout(gtx,
+				layout.Rigid(func(gtx C) D {
+					return layout.Flex{Alignment: layout.Baseline}.Layout(gtx,
+						layout.Flexed(third, func(gtx C) D {
+							return inset.Layout(gtx, material.Button(th, &increaseBtn, "Double list length").Layout)
+						}),
+						layout.Flexed(third, func(gtx C) D {
+							return layout.Center.Layout(gtx, func(gtx C) D {
+								return material.Body1(th, "Current List Length: "+strconv.Itoa(length)).Layout(gtx)
+							})
+						}),
+						layout.Flexed(third, func(gtx C) D {
+							return inset.Layout(gtx, material.Button(th, &decreaseBtn, "Halve list length").Layout)
+						}),
+					)
+				}),
+				layout.Flexed(1, func(gtx C) D {
+					// Track how many items we are laying out
+					var visibleCount int
+					dims := list.Layout(gtx, length, func(gtx C, index int) D {
+						visibleCount++
+						return layout.Center.Layout(gtx, material.H3(th, "List item #"+strconv.Itoa(index)).Layout)
+					})
+					// Compute (using the heuristic that each item is the same vertical height)
+					// the fraction of all items that are currently visible
+					visibleFraction := float32(visibleCount) / float32(length)
+					// Compute how far through the list items we have scrolled
+					scrollDepth := float32(list.Position.First) / float32(length)
+
+					// Lay out the scroll bar
+					bar := scroll.DefaultBar(&indicator, scrollDepth, visibleFraction)
+					bar.Layout(gtx)
+					return dims
+				}),
+			)
+			e.Frame(gtx.Ops)
+		}
+	}
+}

@@ 8,6 8,7 @@ require (
 	git.sr.ht/~whereswaldon/haptic v0.0.0-20201207220958-78675dee81dd
 	git.sr.ht/~whereswaldon/niotify v0.0.3
 	git.sr.ht/~whereswaldon/outlay v0.0.0-20201207220906-cbe824700857
+	git.sr.ht/~whereswaldon/scroll v0.0.0-20201208022259-cc815a044b0b
 	github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7
 	github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4
 	github.com/google/go-github/v24 v24.0.1

@@ 12,6 12,8 @@ git.sr.ht/~whereswaldon/niotify v0.0.3 h1:EWRqPOzqTLU92A9h207LkS/U/nQxuawJ0PF7UE
 git.sr.ht/~whereswaldon/niotify v0.0.3/go.mod h1:itJ9vAQqq8+liURizx7mAdIY4o8gRDF6SAVfswYVg1U=
 git.sr.ht/~whereswaldon/outlay v0.0.0-20201207220906-cbe824700857 h1:Sc+1cZRrwGyiBYgqIto5OlK+RTea1T7FYmZj+JC6RZI=
 git.sr.ht/~whereswaldon/outlay v0.0.0-20201207220906-cbe824700857/go.mod h1:basiujMeRXbgNAivgbiWlxy+gsS0oO70suSRSZ96Nw4=
+git.sr.ht/~whereswaldon/scroll v0.0.0-20201208022259-cc815a044b0b h1:KzG0qB0Vxr6X3kgvYV2HTSjZFbcIx6YiZvbxD+hZIAU=
+git.sr.ht/~whereswaldon/scroll v0.0.0-20201208022259-cc815a044b0b/go.mod h1:/AM8KrZLPyehiTttCs4hYx+9NtV2EaQe4rBGyblqHGo=
 git.wow.st/gmp/jni v0.0.0-20200619201040-d0d3f316ae09/go.mod h1:lfKZKu2afBKJODTFgDNIaBfhq6qmQS0xsS/phLO5Urk=
 git.wow.st/gmp/jni v0.0.0-20200827154156-014cd5c7c4c0 h1:Ynp3h+TC8k1clvf45D28VFQlmy0bPx8M/MG5bB24Vj8=
 git.wow.st/gmp/jni v0.0.0-20200827154156-014cd5c7c4c0/go.mod h1:+axXBRUTIDlCeE73IKeD/os7LoEnTKdkp8/gQOFjqyo=