Return the value of paginator.TotalPages in SetTotalPages...

when the given number of items is below 1.

.github/workflows/build.yml

@@ -0,0 +1,28 @@
+name: build
+on: [push, pull_request]
+jobs:
+  test:
+    strategy:
+      matrix:
+        go-version: [~1.13, ^1]
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    env:
+      GO111MODULE: "on"
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Download Go modules
+        run: go mod download
+
+      - name: Build
+        run: go build -v ./...
+
+      - name: Test
+        run: go test ./...

.github/workflows/coverage.yml

@@ -0,0 +1,28 @@
+name: coverage
+on: [push, pull_request]
+
+jobs:
+  coverage:
+    strategy:
+      matrix:
+        go-version: [^1]
+        os: [ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    env:
+      GO111MODULE: "on"
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Coverage
+        env:
+          COVERALLS_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          go test -race -covermode atomic -coverprofile=profile.cov ./...
+          GO111MODULE=off go get github.com/mattn/goveralls
+          $(go env GOPATH)/bin/goveralls -coverprofile=profile.cov -service=github

.github/workflows/lint.yml

@@ -0,0 +1,20 @@
+name: lint
+on: [push, pull_request]
+
+jobs:
+  golangci:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v2
+        with:
+          # Required: the version of golangci-lint is required and must be specified without patch version: we always use the latest patch version.
+          version: v1.30
+          # Optional: golangci-lint command line arguments.
+          args: --issues-exit-code=0
+          # Optional: working directory, useful for monorepos
+          # working-directory: somedir
+          # Optional: show only new issues if it's a pull request. The default value is `false`.
+          only-new-issues: true

.golangci.yml

@@ -0,0 +1,26 @@
+run:
+  tests: false
+
+issues:
+  max-issues-per-linter: 0
+  max-same-issues: 0
+
+linters:
+  enable:
+    - bodyclose
+    - dupl
+    - exportloopref
+    - goconst
+    - godot
+    - godox
+    - goimports
+    - gomnd
+    - goprintffuncname
+    - gosec
+    - misspell
+    - prealloc
+    - rowserrcheck
+    - sqlclosecheck
+    - unconvert
+    - unparam
+    - whitespace

README.md

@@ -1,9 +1,80 @@
-# Tea Party
+Bubbles
+=======
 
-Components for [Tea](https://github.com/charmbraclet/tea)
+[![Latest Release](https://img.shields.io/github/release/charmbracelet/bubbles.svg)](https://github.com/charmbracelet/bubbles/releases)
+[![GoDoc](https://godoc.org/github.com/golang/gddo?status.svg)](https://pkg.go.dev/github.com/charmbracelet/bubbles)
+[![Build Status](https://github.com/charmbracelet/bubbles/workflows/build/badge.svg)](https://github.com/charmbracelet/bubbles/actions)
+[![Go ReportCard](http://goreportcard.com/badge/charmbracelet/bubbles)](http://goreportcard.com/report/charmbracelet/bubbles)
+
+Some components for [Bubble Tea](https://github.com/charmbracelet/bubbletea) applications.
+
+These components are used in production in [Glow][glow] and [Charm][charm].
+
+[glow]: https://github.com/charmbracelet/glow
+[charm]: https://github.com/charmbracelet/charm
+
+
+## Spinner
+
+<img src="https://stuff.charm.sh/bubbles-examples/spinner.gif" width="400" alt="Spinner Example">
+
+A spinner, useful for indicating that some kind an operation is happening.
+There are a couple default ones, but you can also pass your own ”frames.”
+
+* [Example code](https://github.com/charmbracelet/tea/tree/master/examples/spinner/main.go)
+
+
+## Text Input
+
+<img src="https://stuff.charm.sh/bubbles-examples/textinput.gif" width="400" alt="Text Input Example">
+
+A text input field, akin to an `<input type="text">` in HTML. Supports unicode,
+pasting, in-place scrolling when the value exceeds the width of the element and
+the common, and many customization options.
+
+* [Example code, one field](https://github.com/charmbracelet/tea/tree/master/examples/textinput/main.go)
+* [Example code, many fields](https://github.com/charmbracelet/tea/tree/master/examples/textinputs/main.go)
+
+
+## Paginator
+
+<img src="https://stuff.charm.sh/bubbles-examples/pagination.gif" width="200" alt="Paginator Example">
+
+A component for handling pagination logic and optionally drawing pagination UI.
+Supports "dot-style" pagination (similar to what you might see on iOS) and
+numeric page numbering, but you could also just use this component for the
+logic and visualize pagination however you like.
+
+This component is used in [Glow][glow] to browse documents and [Charm][charm] to
+browse SSH keys.
+
+
+## Viewport
+
+<img src="https://stuff.charm.sh/bubbles-examples/viewport.gif" width="600" alt="Viewport Example">
+
+A viewport for vertically scrolling content. Optionally includes standard
+pager keybindings and mouse wheel support. A high performance mode is available
+for applications which make use of the alterate screen buffer.
+
+* [Example code](https://github.com/charmbracelet/tea/tree/master/examples/pager/main.go)
+
+This component is well complimented with [Reflow][reflow] for ANSI-aware
+indenting and text wrapping.
+
+[reflow]: https://github.com/muesli/reflow
 
-⚠️  This project is a pre-release! Check back later.
 
 ## License
 
 [MIT](https://github.com/charmbracelet/teaparty/raw/master/LICENSE)
+
+
+***
+
+Part of [Charm](https://charm.sh).
+
+<a href="https://charm.sh/"><img alt="the Charm logo" src="https://stuff.charm.sh/charm-badge.jpg" width="400"></a>
+
+Charm热爱开源! / Charm loves open source!
+

go.mod

@@ -3,8 +3,10 @@ module github.com/charmbracelet/bubbles
 go 1.13
 
 require (
-	github.com/charmbracelet/bubbletea v0.8.0
-	github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83
-	golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9 // indirect
-	golang.org/x/sys v0.0.0-20200602225109-6fdc65e7d980 // indirect
+	github.com/atotto/clipboard v0.1.2
+	github.com/charmbracelet/bubbletea v0.12.1
+	github.com/mattn/go-runewidth v0.0.9
+	github.com/muesli/termenv v0.7.4
+	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 // indirect
+	golang.org/x/sys v0.0.0-20201020230747-6e5568b54d1a // indirect
 )

go.sum

@@ -1,26 +1,35 @@
-github.com/charmbracelet/bubbletea v0.8.0 h1:ruZFaFF+2kgCI1IwNG40KTYDW5ZvE2+hPy4odlBdUko=
-github.com/charmbracelet/bubbletea v0.8.0/go.mod h1:DzNhKkQQJI30eb+kBcaOs1+z86zTSqcMgSHoFY+uCsg=
+github.com/atotto/clipboard v0.1.2 h1:YZCtFu5Ie8qX2VmVTBnrqLSiU9XOWwqNRmdT3gIQzbY=
+github.com/atotto/clipboard v0.1.2/go.mod h1:ZY9tmq7sm5xIbd9bOK4onWV4S6X0u6GY7Vn0Yu86PYI=
+github.com/charmbracelet/bubbletea v0.12.1 h1:t21pkG2IDBRduPbt2J64Dx5yt8yIidAkXwhhrc11SzY=
+github.com/charmbracelet/bubbletea v0.12.1/go.mod h1:3gZkYELUOiEUOp0bTInkxguucy/xRbGSOcbMs1geLxg=
+github.com/containerd/console v1.0.1 h1:u7SFAJyRqWcG6ogaMAx3KjSTy1e3hT9QxqX7Jco7dRc=
+github.com/containerd/console v1.0.1/go.mod h1:XUsP6YE/mKtz6bxc+I8UiKKTP04qjQL4qcS3XoQ5xkw=
 github.com/google/goterm v0.0.0-20190703233501-fc88cf888a3f h1:5CjVwnuUcp5adK4gmY6i72gpVFVnZDP2h5TmPScB6u4=
 github.com/google/goterm v0.0.0-20190703233501-fc88cf888a3f/go.mod h1:nOFQdrUlIlx6M6ODdSpBj1NVA+VgLC6kmw60mkw34H4=
 github.com/lucasb-eyer/go-colorful v1.0.3 h1:QIbQXiugsb+q10B+MI+7DI1oQLdmnep86tWFlaaUAac=
 github.com/lucasb-eyer/go-colorful v1.0.3/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
-github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83 h1:AfshZBlqAwhCZ27NJ1aPlMcPBihF1squ1GpaollhLQk=
-github.com/muesli/termenv v0.5.3-0.20200526053627-d728968dcf83/go.mod h1:O1/I6sw+6KcrgAmcs6uiUVr7Lui+DNVbHTzt9Lm/PlI=
-github.com/pkg/term v0.0.0-20200520122047-c3ffed290a03 h1:pd4YKIqCB0U7O2I4gWHgEUA2mCEOENmco0l/bM957bU=
-github.com/pkg/term v0.0.0-20200520122047-c3ffed290a03/go.mod h1:Z9+Ul5bCbBKnbCvdOWbLqTHhJiYV414CURZJba6L8qA=
+github.com/mattn/go-runewidth v0.0.9 h1:Lm995f3rfxdpd6TSmuVCHVb/QhupuXlYr8sCI/QdE+0=
+github.com/mattn/go-runewidth v0.0.9/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
+github.com/muesli/termenv v0.7.2 h1:r1raklL3uKE7rOvWgSenmEm2px+dnc33OTisZ8YR1fw=
+github.com/muesli/termenv v0.7.2/go.mod h1:ct2L5N2lmix82RaY3bMWwVu/jUFc9Ule0KGDCiKYPh8=
+github.com/muesli/termenv v0.7.4 h1:/pBqvU5CpkY53tU0vVn+xgs2ZTX63aH5nY+SSps5Xa8=
+github.com/muesli/termenv v0.7.4/go.mod h1:pZ7qY9l3F7e5xsAOS0zCew2tME+p7bWeBkotCEcIIcc=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20200510223506-06a226fb4e37 h1:cg5LA/zNPRzIXIWSCxQW10Rvpy94aQh3LT/ShoCpkHw=
-golang.org/x/crypto v0.0.0-20200510223506-06a226fb4e37/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9 h1:vEg9joUBmeBcK9iSJftGNf3coIG4HqZElCPehJsfAYM=
-golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/crypto v0.0.0-20201012173705-84dcc777aaee h1:4yd7jl+vXjalO5ztz6Vc1VADv+S/80LGJmyl1ROJ2AI=
+golang.org/x/crypto v0.0.0-20201012173705-84dcc777aaee/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 h1:pLI5jrR7OSLijeIDcmRxNmw2api+jEfxLoykJVice/E=
+golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20200523222454-059865788121 h1:rITEj+UZHYC927n8GT97eC3zrpzXdb/voyeOuVKS46o=
-golang.org/x/sys v0.0.0-20200523222454-059865788121/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20200602225109-6fdc65e7d980 h1:OjiUf46hAmXblsZdnoSXsEUSKU8r1UEzcL5RVZ4gO9Y=
-golang.org/x/sys v0.0.0-20200602225109-6fdc65e7d980/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200916030750-2334cc1a136f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201009025420-dfb3f7c4e634 h1:bNEHhJCnrwMKNMmOx3yAynp5vs5/gRy+XWFtZFu7NBM=
+golang.org/x/sys v0.0.0-20201009025420-dfb3f7c4e634/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201020230747-6e5568b54d1a h1:e3IU37lwO4aq3uoRKINC7JikojFmE5gO7xhfxs8VC34=
+golang.org/x/sys v0.0.0-20201020230747-6e5568b54d1a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

paginator/paginator.go

@@ -13,7 +13,7 @@ import (
 // Type specifies the way we render pagination.
 type Type int
 
-// Pagination rendering options
+// Pagination rendering options.
 const (
 	Arabic Type = iota
 	Dots
@@ -21,17 +21,18 @@ const (
 
 // Model is the Tea model for this user interface.
 type Model struct {
-	Type             Type
-	Page             int
-	PerPage          int
-	TotalPages       int
-	ActiveDot        string
-	InactiveDot      string
-	ArabicFormat     string
-	UseLeftRightKeys bool
-	UseUpDownKeys    bool
-	UseHLKeys        bool
-	UseJKKeys        bool
+	Type              Type
+	Page              int
+	PerPage           int
+	TotalPages        int
+	ActiveDot         string
+	InactiveDot       string
+	ArabicFormat      string
+	UsePgUpPgDownKeys bool
+	UseLeftRightKeys  bool
+	UseUpDownKeys     bool
+	UseHLKeys         bool
+	UseJKKeys         bool
 }
 
 // SetTotalPages is a helper function for calculatng the total number of pages
@@ -39,8 +40,8 @@ type Model struct {
 // used for other things beyond navigating sets. Note that it both returns the
 // number of total pages and alters the model.
 func (m *Model) SetTotalPages(items int) int {
-	if items == 0 {
-		return 0
+	if items < 1 {
+		return m.TotalPages
 	}
 	n := items / m.PerPage
 	if items%m.PerPage > 0 {
@@ -98,17 +99,18 @@ func (m Model) OnLastPage() bool {
 // NewModel creates a new model with defaults.
 func NewModel() Model {
 	return Model{
-		Type:             Arabic,
-		Page:             0,
-		PerPage:          1,
-		TotalPages:       1,
-		ActiveDot:        "•",
-		InactiveDot:      "○",
-		ArabicFormat:     "%d/%d",
-		UseLeftRightKeys: true,
-		UseUpDownKeys:    false,
-		UseHLKeys:        true,
-		UseJKKeys:        false,
+		Type:              Arabic,
+		Page:              0,
+		PerPage:           1,
+		TotalPages:        1,
+		ActiveDot:         "•",
+		InactiveDot:       "○",
+		ArabicFormat:      "%d/%d",
+		UsePgUpPgDownKeys: true,
+		UseLeftRightKeys:  true,
+		UseUpDownKeys:     false,
+		UseHLKeys:         true,
+		UseJKKeys:         false,
 	}
 }
 
@@ -116,6 +118,14 @@ func NewModel() Model {
 func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 	switch msg := msg.(type) {
 	case tea.KeyMsg:
+		if m.UsePgUpPgDownKeys {
+			switch msg.String() {
+			case "pgup":
+				m.PrevPage()
+			case "pgdown":
+				m.NextPage()
+			}
+		}
 		if m.UseLeftRightKeys {
 			switch msg.String() {
 			case "left":
@@ -154,11 +164,7 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 }
 
 // View renders the pagination to a string.
-func View(model tea.Model) string {
-	m, ok := model.(Model)
-	if !ok {
-		return "could not perform assertion on model"
-	}
+func View(m Model) string {
 	switch m.Type {
 	case Dots:
 		return dotsView(m)

spinner/spinner.go

@@ -7,25 +7,17 @@ import (
 	"github.com/muesli/termenv"
 )
 
+const (
+	defaultFPS = time.Second / 10
+)
+
 // Spinner is a set of frames used in animating the spinner.
-type Spinner = int
-
-// Available types of spinners
-const (
-	Line Spinner = iota
-	Dot
-)
-
-const (
-	defaultFPS = 9
-)
+type Spinner = []string
 
 var (
-	// Spinner frames
-	spinners = map[Spinner][]string{
-		Line: {"|", "/", "-", "\\"},
-		Dot:  {"⣾ ", "⣽ ", "⣻ ", "⢿ ", "⡿ ", "⣟ ", "⣯ ", "⣷ "},
-	}
+	// Some spinners to choose from. You could also make your own.
+	Line = Spinner([]string{"|", "/", "-", "\\"})
+	Dot  = Spinner([]string{"⣾ ", "⣽ ", "⣻ ", "⢿ ", "⡿ ", "⣟ ", "⣯ ", "⣷ "})
 
 	color = termenv.ColorProfile().Color
 )
@@ -35,10 +27,10 @@ var (
 type Model struct {
 
 	// Type is the set of frames to use. See Spinner.
-	Type Spinner
+	Frames Spinner
 
-	// FPS is the speed at which the ticker should tick
-	FPS int
+	// FPS is the speed at which the ticker should tick.
+	FPS time.Duration
 
 	// ForegroundColor sets the background color of the spinner. It can be a
 	// hex code or one of the 256 ANSI colors. If the terminal emulator can't
@@ -52,67 +44,129 @@ type Model struct {
 	// (per github.com/muesli/termenv).
 	BackgroundColor string
 
-	// CustomMsgFunc can be used to a custom message on tick. This can be
-	// useful when you have spinners in different parts of your application and
-	// want to differentiate between the messages for clarity and simplicity.
-	// If nil, this setting is ignored.
-	CustomMsgFunc func() tea.Msg
+	// MinimumLifetime is the minimum amount of time the spinner can run. Any
+	// logic around this can be implemented in view that implements this
+	// spinner. If HideFor is set MinimumLifetime will be added on top of
+	// HideFor. In other words, if HideFor is 100ms and MinimumLifetime is
+	// 200ms then MinimumLifetime will expire after 300ms.
+	//
+	// MinimumLifetime is optional.
+	//
+	// This is considered experimental and may not appear in future versions of
+	// this library.
+	MinimumLifetime time.Duration
 
-	frame int
+	// HideFor can be used to wait to show the spinner until a certain amount
+	// of time has passed. This can be useful for preventing flicking when load
+	// times are very fast.
+	// Optional.
+	//
+	// This is considered experimental and may not appear in future versions of
+	// this library.
+	HideFor time.Duration
+
+	frame     int
+	startTime time.Time
+}
+
+// Start resets resets the spinner start time. For use with MinimumLifetime and
+// MinimumStartTime. Optional.
+//
+// This is considered experimental and may not appear in future versions of
+// this library.
+func (m *Model) Start() {
+	m.startTime = time.Now()
+}
+
+// hidden returns whether or not Model.HideFor is in effect.
+func (m Model) hidden() bool {
+	if m.startTime.IsZero() {
+		return false
+	}
+	if m.HideFor == 0 {
+		return false
+	}
+	return m.startTime.Add(m.HideFor).After(time.Now())
+}
+
+// finished returns whether Model.MinimumLifetimeReached has been met.
+func (m Model) finished() bool {
+	if m.startTime.IsZero() {
+		return true
+	}
+	if m.MinimumLifetime == 0 {
+		return true
+	}
+	return m.startTime.Add(m.HideFor).Add(m.MinimumLifetime).Before(time.Now())
+}
+
+// Visible returns whether or not the view should be rendered. Works in
+// conjunction with Model.HideFor and Model.MinimumLifetimeReached. You should
+// use this message directly to determine whether or not to render this view in
+// the parent view and whether to continue sending spin messaging in the
+// parent update function.
+//
+// Also note that using this function is optional and generally considered for
+// advanced use only. Most of the time your application logic will determine
+// whether or not this view should be used.
+//
+// This is considered experimental and may not appear in future versions of
+// this library.
+func (m Model) Visible() bool {
+	return !m.hidden() && !m.finished()
 }
 
 // NewModel returns a model with default values.
 func NewModel() Model {
 	return Model{
-		Type: Line,
-		FPS:  defaultFPS,
+		Frames: Line,
+		FPS:    defaultFPS,
 	}
 }
 
 // TickMsg indicates that the timer has ticked and we should render a frame.
-type TickMsg struct{}
+type TickMsg struct {
+	Time time.Time
+}
 
 // Update is the Tea update function. This will advance the spinner one frame
 // every time it's called, regardless the message passed, so be sure the logic
 // is setup so as not to call this Update needlessly.
 func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
-	m.frame++
-	if m.frame >= len(spinners[m.Type]) {
-		m.frame = 0
-	}
-	if m.CustomMsgFunc != nil {
+	if _, ok := msg.(TickMsg); ok {
+		m.frame++
+		if m.frame >= len(m.Frames) {
+			m.frame = 0
+		}
 		return m, Tick(m)
 	}
-	return m, Tick(m)
+	return m, nil
 }
 
 // View renders the model's view.
 func View(model Model) string {
-	s := spinners[model.Type]
-	if model.frame >= len(s) {
-		return "[error]"
+	if model.frame >= len(model.Frames) {
+		return "error"
 	}
 
-	str := s[model.frame]
+	frame := model.Frames[model.frame]
 
 	if model.ForegroundColor != "" || model.BackgroundColor != "" {
 		return termenv.
-			String(str).
+			String(frame).
 			Foreground(color(model.ForegroundColor)).
 			Background(color(model.BackgroundColor)).
 			String()
 	}
 
-	return str
+	return frame
 }
 
 // Tick is the command used to advance the spinner one frame.
-func Tick(model Model) tea.Cmd {
-	return func() tea.Msg {
-		time.Sleep(time.Second / time.Duration(model.FPS))
-		if model.CustomMsgFunc != nil {
-			return model.CustomMsgFunc()
+func Tick(m Model) tea.Cmd {
+	return tea.Tick(m.FPS, func(t time.Time) tea.Msg {
+		return TickMsg{
+			Time: t,
 		}
-		return TickMsg{}
-	}
+	})
 }

textinput/textinput.go

@@ -5,36 +5,55 @@ import (
 	"time"
 	"unicode"
 
+	"github.com/atotto/clipboard"
 	tea "github.com/charmbracelet/bubbletea"
+	rw "github.com/mattn/go-runewidth"
 	"github.com/muesli/termenv"
 )
 
+const defaultBlinkSpeed = time.Millisecond * 530
+
 const (
-	defaultBlinkSpeed = time.Millisecond * 600
+	// EchoNormal displays text as is. This is the default behavior.
+	EchoNormal EchoMode = iota
+
+	// EchoPassword displays the EchoCharacter mask instead of actual
+	// characters.  This is commonly used for password fields.
+	EchoPassword
+
+	// EchoNone displays nothing as characters are entered. This is commonly
+	// seen for password fields on the command line.
+	EchoNone
+
+	// EchoOnEdit
 )
 
+// EchoMode sets the input behavior of the text input field.
+type EchoMode int
+
 var (
-	// color is a helper for returning colors
+	// color is a helper for returning colors.
 	color func(s string) termenv.Color = termenv.ColorProfile().Color
 )
 
-// ErrMsg indicates there's been an error. We don't handle errors in the this
-// package; we're expecting errors to be handle in the program that implements
-// this text input.
-type ErrMsg error
-
-// Model is the Tea model for this text input element.
+// Model is the Bubble Tea model for this text input element.
 type Model struct {
-	Err              error
-	Prompt           string
-	Cursor           string
-	BlinkSpeed       time.Duration
-	Placeholder      string
+	Err error
+
+	Prompt      string
+	Placeholder string
+
+	Cursor     string
+	BlinkSpeed time.Duration
+
 	TextColor        string
 	BackgroundColor  string
 	PlaceholderColor string
 	CursorColor      string
 
+	EchoMode      EchoMode
+	EchoCharacter rune
+
 	// CharLimit is the maximum amount of characters this input element will
 	// accept. If 0 or less, there's no limit.
 	CharLimit int
@@ -44,59 +63,60 @@ type Model struct {
 	// viewport. If 0 or less this setting is ignored.
 	Width int
 
-	// Underlying text value
-	value string
+	// Underlying text value.
+	value []rune
 
 	// Focus indicates whether user input focus should be on this input
 	// component. When false, don't blink and ignore keyboard input.
 	focus bool
 
-	// Cursor blink state
+	// Cursor blink state.
 	blink bool
 
-	// Cursor position
+	// Cursor position.
 	pos int
 
 	// Used to emulate a viewport when width is set and the content is
-	// overflowing
-	offset int
+	// overflowing.
+	offset      int
+	offsetRight int
 }
 
 // SetValue sets the value of the text input.
 func (m *Model) SetValue(s string) {
-	if m.CharLimit > 0 && len(s) > m.CharLimit {
-		m.value = s[:m.CharLimit]
+	runes := []rune(s)
+	if m.CharLimit > 0 && len(runes) > m.CharLimit {
+		m.value = runes[:m.CharLimit]
 	} else {
-		m.value = s
+		m.value = runes
 	}
 	if m.pos > len(m.value) {
-		m.pos = len(m.value)
+		m.SetCursor(len(m.value))
 	}
 	m.handleOverflow()
 }
 
 // Value returns the value of the text input.
 func (m Model) Value() string {
-	return m.value
+	return string(m.value)
 }
 
-// Cursor start moves the cursor to the given position. If the position is out
-// of bounds the cursor will be moved to the start or end accordingly.
+// SetCursor start moves the cursor to the given position. If the position is
+// out of bounds the cursor will be moved to the start or end accordingly.
 func (m *Model) SetCursor(pos int) {
-	m.pos = max(0, min(len(m.value), pos))
+	m.pos = clamp(pos, 0, len(m.value))
+	m.blink = false
 	m.handleOverflow()
 }
 
 // CursorStart moves the cursor to the start of the field.
 func (m *Model) CursorStart() {
-	m.pos = 0
-	m.handleOverflow()
+	m.SetCursor(0)
 }
 
 // CursorEnd moves the cursor to the end of the field.
 func (m *Model) CursorEnd() {
-	m.pos = len(m.value)
-	m.handleOverflow()
+	m.SetCursor(len(m.value))
 }
 
 // Focused returns the focus state on the model.
@@ -118,23 +138,101 @@ func (m *Model) Blur() {
 
 // Reset sets the input to its default state with no input.
 func (m *Model) Reset() {
-	m.value = ""
-	m.offset = 0
-	m.pos = 0
-	m.blink = false
+	m.value = nil
+	m.SetCursor(0)
+}
+
+// Paste pastes the contents of the clipboard into the text area (if supported).
+func (m *Model) Paste() {
+	pasteString, err := clipboard.ReadAll()
+	if err != nil {
+		m.Err = err
+	}
+	paste := []rune(pasteString)
+
+	var availSpace int
+	if m.CharLimit > 0 {
+		availSpace = m.CharLimit - len(m.value)
+	}
+
+	// If the char limit's been reached cancel
+	if m.CharLimit > 0 && availSpace <= 0 {
+		return
+	}
+
+	// If there's not enough space to paste the whole thing cut the pasted
+	// runes down so they'll fit
+	if m.CharLimit > 0 && availSpace < len(paste) {
+		paste = paste[:len(paste)-availSpace]
+	}
+
+	// Stuff before and after the cursor
+	head := m.value[:m.pos]
+	tailSrc := m.value[m.pos:]
+	tail := make([]rune, len(tailSrc))
+	copy(tail, tailSrc)
+
+	// Insert pasted runes
+	for _, r := range paste {
+		head = append(head, r)
+		m.pos++
+		if m.CharLimit > 0 {
+			availSpace--
+			if availSpace <= 0 {
+				break
+			}
+		}
+	}
+
+	// Put it all back together
+	m.value = append(head, tail...)
+
+	// Reset blink state and run overflow checks
+	m.SetCursor(m.pos)
 }
 
 // If a max width is defined, perform some logic to treat the visible area
 // as a horizontally scrolling viewport.
 func (m *Model) handleOverflow() {
-	if m.Width > 0 {
-		overflow := max(0, len(m.value)-m.Width)
+	if m.Width <= 0 || rw.StringWidth(string(m.value)) <= m.Width {
+		m.offset = 0
+		m.offsetRight = len(m.value)
+		return
+	}
 
-		if overflow > 0 && m.pos < m.offset {
-			m.offset = max(0, min(len(m.value), m.pos))
-		} else if overflow > 0 && m.pos >= m.offset+m.Width {
-			m.offset = max(0, m.pos-m.Width)
+	// Correct right offset if we've deleted characters
+	m.offsetRight = min(m.offsetRight, len(m.value))
+
+	if m.pos < m.offset {
+		m.offset = m.pos
+
+		w := 0
+		i := 0
+		runes := m.value[m.offset:]
+
+		for i < len(runes) && w <= m.Width {
+			w += rw.RuneWidth(runes[i])
+			if w <= m.Width+1 {
+				i++
+			}
 		}
+
+		m.offsetRight = m.offset + i
+	} else if m.pos >= m.offsetRight {
+		m.offsetRight = m.pos
+
+		w := 0
+		runes := m.value[:m.offsetRight]
+		i := len(runes) - 1
+
+		for i > 0 && w < m.Width {
+			w += rw.RuneWidth(runes[i])
+			if w <= m.Width {
+				i--
+			}
+		}
+
+		m.offset = m.offsetRight - (len(runes) - 1 - i)
 	}
 }
 
@@ -158,6 +256,67 @@ func (m *Model) colorPlaceholder(s string) string {
 		String()
 }
 
+// deleteWordLeft deletes the word left to the cursor.
+func (m *Model) deleteWordLeft() {
+	if m.pos == 0 || len(m.value) == 0 {
+		return
+	}
+
+	i := m.pos
+	m.SetCursor(m.pos - 1)
+	for unicode.IsSpace(m.value[m.pos]) {
+		// ignore series of whitespace before cursor
+		m.SetCursor(m.pos - 1)
+	}
+
+	for m.pos > 0 {
+		if !unicode.IsSpace(m.value[m.pos]) {
+			m.SetCursor(m.pos - 1)
+		} else {
+			if m.pos > 0 {
+				// keep the previous space
+				m.SetCursor(m.pos + 1)
+			}
+			break
+		}
+	}
+
+	if i > len(m.value) {
+		m.value = m.value[:m.pos]
+	} else {
+		m.value = append(m.value[:m.pos], m.value[i:]...)
+	}
+}
+
+// deleteWordRight deletes the word right to the cursor.
+func (m *Model) deleteWordRight() {
+	if m.pos >= len(m.value) || len(m.value) == 0 {
+		return
+	}
+
+	i := m.pos
+	m.SetCursor(m.pos + 1)
+	for unicode.IsSpace(m.value[m.pos]) {
+		// ignore series of whitespace after cursor
+		m.SetCursor(m.pos + 1)
+	}
+
+	for m.pos < len(m.value) {
+		if !unicode.IsSpace(m.value[m.pos]) {
+			m.SetCursor(m.pos + 1)
+		} else {
+			break
+		}
+	}
+
+	if m.pos > len(m.value) {
+		m.value = m.value[:i]
+	} else {
+		m.value = append(m.value[:i], m.value[m.pos:]...)
+	}
+	m.SetCursor(i)
+}
+
 func (m *Model) wordLeft() {
 	if m.pos == 0 || len(m.value) == 0 {
 		return
@@ -166,8 +325,8 @@ func (m *Model) wordLeft() {
 	i := m.pos - 1
 
 	for i >= 0 {
-		if unicode.IsSpace(rune(m.value[i])) {
-			m.pos--
+		if unicode.IsSpace(m.value[i]) {
+			m.SetCursor(m.pos - 1)
 			i--
 		} else {
 			break
@@ -175,8 +334,8 @@ func (m *Model) wordLeft() {
 	}
 
 	for i >= 0 {
-		if !unicode.IsSpace(rune(m.value[i])) {
-			m.pos--
+		if !unicode.IsSpace(m.value[i]) {
+			m.SetCursor(m.pos - 1)
 			i--
 		} else {
 			break
@@ -192,8 +351,8 @@ func (m *Model) wordRight() {
 	i := m.pos
 
 	for i < len(m.value) {
-		if unicode.IsSpace(rune(m.value[i])) {
-			m.pos++
+		if unicode.IsSpace(m.value[i]) {
+			m.SetCursor(m.pos + 1)
 			i++
 		} else {
 			break
@@ -201,8 +360,8 @@ func (m *Model) wordRight() {
 	}
 
 	for i < len(m.value) {
-		if !unicode.IsSpace(rune(m.value[i])) {
-			m.pos++
+		if !unicode.IsSpace(m.value[i]) {
+			m.SetCursor(m.pos + 1)
 			i++
 		} else {
 			break
@@ -210,21 +369,38 @@ func (m *Model) wordRight() {
 	}
 }
 
+func (m Model) echoTransform(v string) string {
+	switch m.EchoMode {
+	case EchoPassword:
+		return strings.Repeat(string(m.EchoCharacter), rw.StringWidth(v))
+	case EchoNone:
+		return ""
+
+	default:
+		return v
+	}
+}
+
 // BlinkMsg is sent when the cursor should alternate it's blinking state.
 type BlinkMsg struct{}
 
 // NewModel creates a new model with default settings.
 func NewModel() Model {
 	return Model{
-		Prompt:           "> ",
-		BlinkSpeed:       defaultBlinkSpeed,
-		Placeholder:      "",
+		Prompt:      "> ",
+		Placeholder: "",
+
+		BlinkSpeed: defaultBlinkSpeed,
+
 		TextColor:        "",
 		PlaceholderColor: "240",
 		CursorColor:      "",
-		CharLimit:        0,
 
-		value: "",
+		EchoCharacter: '*',
+
+		CharLimit: 0,
+
+		value: nil,
 		focus: false,
 		blink: true,
 		pos:   0,
@@ -241,12 +417,16 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 	switch msg := msg.(type) {
 	case tea.KeyMsg:
 		switch msg.Type {
-		case tea.KeyBackspace:
-			fallthrough
-		case tea.KeyDelete:
-			if len(m.value) > 0 {
-				m.value = m.value[:m.pos-1] + m.value[m.pos:]
-				m.pos--
+		case tea.KeyBackspace: // delete character before cursor
+			if msg.Alt {
+				m.deleteWordLeft()
+			} else {
+				if len(m.value) > 0 {
+					m.value = append(m.value[:max(0, m.pos-1)], m.value[m.pos:]...)
+					if m.pos > 0 {
+						m.SetCursor(m.pos - 1)
+					}
+				}
 			}
 		case tea.KeyLeft:
 			if msg.Alt { // alt+left arrow, back one word
@@ -254,7 +434,7 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 				break
 			}
 			if m.pos > 0 {
-				m.pos--
+				m.SetCursor(m.pos - 1)
 			}
 		case tea.KeyRight:
 			if msg.Alt { // alt+right arrow, forward one word
@@ -262,30 +442,37 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 				break
 			}
 			if m.pos < len(m.value) {
-				m.pos++
+				m.SetCursor(m.pos + 1)
 			}
+		case tea.KeyCtrlW: // ^W, delete word left of cursor
+			m.deleteWordLeft()
 		case tea.KeyCtrlF: // ^F, forward one character
 			fallthrough
 		case tea.KeyCtrlB: // ^B, back one charcter
 			fallthrough
-		case tea.KeyCtrlA: // ^A, go to beginning
+		case tea.KeyHome, tea.KeyCtrlA: // ^A, go to beginning
 			m.CursorStart()
-		case tea.KeyCtrlD: // ^D, delete char under cursor
+		case tea.KeyDelete, tea.KeyCtrlD: // ^D, delete char under cursor
 			if len(m.value) > 0 && m.pos < len(m.value) {
-				m.value = m.value[:m.pos] + m.value[m.pos+1:]
+				m.value = append(m.value[:m.pos], m.value[m.pos+1:]...)
 			}
-		case tea.KeyCtrlE: // ^E, go to end
+		case tea.KeyCtrlE, tea.KeyEnd: // ^E, go to end
 			m.CursorEnd()
 		case tea.KeyCtrlK: // ^K, kill text after cursor
 			m.value = m.value[:m.pos]
-			m.pos = len(m.value)
+			m.SetCursor(len(m.value))
 		case tea.KeyCtrlU: // ^U, kill text before cursor
 			m.value = m.value[m.pos:]
-			m.pos = 0
+			m.SetCursor(0)
 			m.offset = 0
+		case tea.KeyCtrlV: // ^V paste
+			m.Paste()
 		case tea.KeyRune: // input a regular character
-
 			if msg.Alt {
+				if msg.Rune == 'd' { // alt+d, delete word right of cursor
+					m.deleteWordRight()
+					break
+				}
 				if msg.Rune == 'b' { // alt+b, back one word
 					m.wordLeft()
 					break
@@ -298,14 +485,11 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 
 			// Input a regular character
 			if m.CharLimit <= 0 || len(m.value) < m.CharLimit {
-				m.value = m.value[:m.pos] + string(msg.Rune) + m.value[m.pos:]
-				m.pos++
+				m.value = append(m.value[:m.pos], append([]rune{msg.Rune}, m.value[m.pos:]...)...)
+				m.SetCursor(m.pos + 1)
 			}
 		}
 
-	case ErrMsg:
-		m.Err = msg
-
 	case BlinkMsg:
 		m.blink = !m.blink
 		return m, Blink(m)
@@ -317,41 +501,29 @@ func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
 }
 
 // View renders the textinput in its current state.
-func View(model tea.Model) string {
-	m, ok := model.(Model)
-	if !ok {
-		return "could not perform assertion on model"
-	}
-
+func View(m Model) string {
 	// Placeholder text
-	if m.value == "" && m.Placeholder != "" {
+	if len(m.value) == 0 && m.Placeholder != "" {
 		return placeholderView(m)
 	}
 
-	left := m.offset
-	right := 0
-	if m.Width > 0 {
-		right = min(len(m.value), m.offset+m.Width+1)
-	} else {
-		right = len(m.value)
-	}
-	value := m.value[left:right]
-	pos := m.pos - m.offset
-
-	v := m.colorText(value[:pos])
+	value := m.value[m.offset:m.offsetRight]
+	pos := max(0, m.pos-m.offset)
+	v := m.colorText(m.echoTransform(string(value[:pos])))
 
 	if pos < len(value) {
-		v += cursorView(string(value[pos]), m) // cursor and text under it
-		v += m.colorText(value[pos+1:])        // text after cursor
+		v += cursorView(m.echoTransform(string(value[pos])), m)  // cursor and text under it
+		v += m.colorText(m.echoTransform(string(value[pos+1:]))) // text after cursor
 	} else {
 		v += cursorView(" ", m)
 	}
 
 	// If a max width and background color were set fill the empty spaces with
 	// the background color.
-	if m.Width > 0 && len(m.BackgroundColor) > 0 && len(value) <= m.Width {
-		padding := m.Width - len(value)
-		if len(value)+padding <= m.Width && pos < len(value) {
+	valWidth := rw.StringWidth(string(value))
+	if m.Width > 0 && len(m.BackgroundColor) > 0 && valWidth <= m.Width {
+		padding := max(0, m.Width-valWidth)
+		if valWidth+padding <= m.Width && pos < len(value) {
 			padding++
 		}
 		v += strings.Repeat(
@@ -363,7 +535,7 @@ func View(model tea.Model) string {
 	return m.Prompt + v
 }
 
-// placeholderView
+// placeholderView.
 func placeholderView(m Model) string {
 	var (
 		v string
@@ -372,10 +544,7 @@ func placeholderView(m Model) string {
 
 	// Cursor
 	if m.blink && m.PlaceholderColor != "" {
-		v += cursorView(
-			m.colorPlaceholder(p[:1]),
-			m,
-		)
+		v += cursorView(m.colorPlaceholder(p[:1]), m)
 	} else {
 		v += cursorView(p[:1], m)
 	}
@@ -412,6 +581,10 @@ func Blink(model Model) tea.Cmd {
 	}
 }
 
+func clamp(v, low, high int) int {
+	return min(high, max(low, v))
+}
+
 func min(a, b int) int {
 	if a < b {
 		return a

viewport/viewport.go

@@ -1,147 +1,369 @@
 package viewport
 
 import (
+	"math"
 	"strings"
 
 	tea "github.com/charmbracelet/bubbletea"
 )
 
+const (
+	spacebar = " "
+)
+
 // MODEL
 
 type Model struct {
-	Err    error
 	Width  int
 	Height int
-	Y      int
+
+	// YOffset is the vertical scroll position.
+	YOffset int
+
+	// YPosition is the position of the viewport in relation to the terminal
+	// window. It's used in high performance rendering.
+	YPosition int
+
+	// HighPerformanceRendering bypasses the normal Bubble Tea renderer to
+	// provide higher performance rendering. Most of the time the normal Bubble
+	// Tea rendering methods will suffice, but if you're passing content with
+	// a lot of ANSI escape codes you may see improved rendering in certain
+	// terminals with this enabled.
+	//
+	// This should only be used in program occupying the entire terminal,
+	// which is usually via the alternate screen buffer.
+	HighPerformanceRendering bool
 
 	lines []string
 }
 
+// AtTop returns whether or not the viewport is in the very top position.
+func (m Model) AtTop() bool {
+	return m.YOffset <= 0
+}
+
+// AtBottom returns whether or not the viewport is at or past the very bottom
+// position.
+func (m Model) AtBottom() bool {
+	return m.YOffset >= len(m.lines)-1-m.Height
+}
+
+// PastBottom returns whether or not the viewport is scrolled beyond the last
+// line. This can happen when adjusting the viewport height.
+func (m Model) PastBottom() bool {
+	return m.YOffset > len(m.lines)-1-m.Height
+}
+
 // Scrollpercent returns the amount scrolled as a float between 0 and 1.
 func (m Model) ScrollPercent() float64 {
 	if m.Height >= len(m.lines) {
 		return 1.0
 	}
-	y := float64(m.Y)
+	y := float64(m.YOffset)
 	h := float64(m.Height)
-	t := float64(len(m.lines))
-	return y / (t - h)
+	t := float64(len(m.lines) - 1)
+	v := y / (t - h)
+	return math.Max(0.0, math.Min(1.0, v))
 }
 
-// SetContent set the pager's text content.
+// SetContent set the pager's text content. For high performance rendering the
+// Sync command should also be called.
 func (m *Model) SetContent(s string) {
 	s = strings.Replace(s, "\r\n", "\n", -1) // normalize line endings
 	m.lines = strings.Split(s, "\n")
 }
 
-// NewModel creates a new pager model. Pass the dimensions of the pager.
-func NewModel(width, height int) Model {
-	return Model{
-		Width:  width,
-		Height: height,
+// Return the lines that should currently be visible in the viewport.
+func (m Model) visibleLines() (lines []string) {
+	if len(m.lines) > 0 {
+		top := max(0, m.YOffset)
+		bottom := clamp(m.YOffset+m.Height, top, len(m.lines))
+		lines = m.lines[top:bottom]
 	}
+	return lines
 }
 
 // ViewDown moves the view down by the number of lines in the viewport.
 // Basically, "page down".
-func (m *Model) ViewDown() {
-	m.Y = min(len(m.lines)-m.Height, m.Y+m.Height)
+func (m *Model) ViewDown() []string {
+	if m.AtBottom() {
+		return nil
+	}
+
+	m.YOffset = min(
+		m.YOffset+m.Height,      // target
+		len(m.lines)-1-m.Height, // fallback
+	)
+
+	return m.visibleLines()
 }
 
 // ViewUp moves the view up by one height of the viewport. Basically, "page up".
-func (m *Model) ViewUp() {
-	m.Y = max(0, m.Y-m.Height)
-}
+func (m *Model) ViewUp() []string {
+	if m.AtTop() {
+		return nil
+	}
 
-// HalfViewUp moves the view up by half the height of the viewport.
-func (m *Model) HalfViewUp() {
-	m.Y = max(0, m.Y-m.Height/2)
+	m.YOffset = max(
+		m.YOffset-m.Height, // target
+		0,                  // fallback
+	)
+
+	return m.visibleLines()
 }
 
 // HalfViewDown moves the view down by half the height of the viewport.
-func (m *Model) HalfViewDown() {
-	m.Y = min(len(m.lines)-m.Height, m.Y+m.Height/2)
+func (m *Model) HalfViewDown() (lines []string) {
+	if m.AtBottom() {
+		return nil
+	}
+
+	m.YOffset = min(
+		m.YOffset+m.Height/2,    // target
+		len(m.lines)-1-m.Height, // fallback
+	)
+
+	if len(m.lines) > 0 {
+		top := max(m.YOffset+m.Height/2, 0)
+		bottom := clamp(m.YOffset+m.Height, top, len(m.lines)-1)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
 }
 
-// LineDown moves the view up by the given number of lines.
-func (m *Model) LineDown(n int) {
-	m.Y = min(len(m.lines)-m.Height, m.Y+n)
+// HalfViewUp moves the view up by half the height of the viewport.
+func (m *Model) HalfViewUp() (lines []string) {
+	if m.AtTop() {
+		return nil
+	}
+
+	m.YOffset = max(
+		m.YOffset-m.Height/2, // target
+		0,                    // fallback
+	)
+
+	if len(m.lines) > 0 {
+		top := max(m.YOffset, 0)
+		bottom := clamp(m.YOffset+m.Height/2, top, len(m.lines)-1)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
 }
 
 // LineDown moves the view down by the given number of lines.
-func (m *Model) LineUp(n int) {
-	m.Y = max(0, m.Y-n)
+func (m *Model) LineDown(n int) (lines []string) {
+	if m.AtBottom() || n == 0 {
+		return nil
+	}
+
+	// Make sure the number of lines by which we're going to scroll isn't
+	// greater than the number of lines we actually have left before we reach
+	// the bottom.
+	maxDelta := (len(m.lines) - 1) - (m.YOffset + m.Height) // number of lines - viewport bottom edge
+	n = min(n, maxDelta)
+
+	m.YOffset = min(
+		m.YOffset+n,             // target
+		len(m.lines)-1-m.Height, // fallback
+	)
+
+	if len(m.lines) > 0 {
+		top := max(m.YOffset+m.Height-n, 0)
+		bottom := clamp(m.YOffset+m.Height, top, len(m.lines)-1)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
+}
+
+// LineUp moves the view down by the given number of lines. Returns the new
+// lines to show.
+func (m *Model) LineUp(n int) (lines []string) {
+	if m.AtTop() || n == 0 {
+		return nil
+	}
+
+	// Make sure the number of lines by which we're going to scroll isn't
+	// greater than the number of lines we are from the top.
+	n = min(n, m.YOffset)
+
+	m.YOffset = max(m.YOffset-n, 0)
+
+	if len(m.lines) > 0 {
+		top := max(0, m.YOffset)
+		bottom := clamp(m.YOffset+n, top, len(m.lines)-1)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
+}
+
+// GotoTop sets the viewport to the top position.
+func (m *Model) GotoTop() (lines []string) {
+	if m.AtTop() {
+		return nil
+	}
+
+	m.YOffset = 0
+
+	if len(m.lines) > 0 {
+		top := m.YOffset
+		bottom := clamp(m.YOffset+m.Height, top, len(m.lines)-1)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
+}
+
+// GotoTop sets the viewport to the bottom position.
+func (m *Model) GotoBottom() (lines []string) {
+	m.YOffset = max(len(m.lines)-1-m.Height, 0)
+
+	if len(m.lines) > 0 {
+		top := m.YOffset
+		bottom := max(len(m.lines)-1, 0)
+		lines = m.lines[top:bottom]
+	}
+
+	return lines
+}
+
+// COMMANDS
+
+// Sync tells the renderer where the viewport will be located and requests
+// a render of the current state of the viewport. It should be called for the
+// first render and after a window resize.
+//
+// For high performance rendering only.
+func Sync(m Model) tea.Cmd {
+	if len(m.lines) == 0 {
+		return nil
+	}
+
+	// TODO: we should probably use m.visibleLines() rather than these two
+	// expressions.
+	top := max(m.YOffset, 0)
+	bottom := clamp(m.YOffset+m.Height, 0, len(m.lines)-1)
+
+	return tea.SyncScrollArea(
+		m.lines[top:bottom],
+		m.YPosition,
+		m.YPosition+m.Height,
+	)
+}
+
+// ViewDown is a high performance command that moves the viewport up by a given
+// numer of lines. Use Model.ViewDown to get the lines that should be rendered.
+// For example:
+//
+//     lines := model.ViewDown(1)
+//     cmd := ViewDown(m, lines)
+//
+func ViewDown(m Model, lines []string) tea.Cmd {
+	if len(lines) == 0 {
+		return nil
+	}
+	return tea.ScrollDown(lines, m.YPosition, m.YPosition+m.Height)
+}
+
+// ViewUp is a high performance command the moves the viewport down by a given
+// number of lines height. Use Model.ViewDown to get the lines that should be
+// rendered.
+func ViewUp(m Model, lines []string) tea.Cmd {
+	if len(lines) == 0 {
+		return nil
+	}
+	return tea.ScrollUp(lines, m.YPosition, m.YPosition+m.Height)
 }
 
 // UPDATE
 
-// Update runs the update loop with default keybindings. To define your own
-// keybindings use the methods on Model.
+// Update runs the update loop with default keybindings similar to popular
+// pagers. To define your own keybindings use the methods on Model (i.e.
+// Model.LineDown()) and define your own update function.
 func Update(msg tea.Msg, m Model) (Model, tea.Cmd) {
-	switch msg := msg.(type) {
+	var cmd tea.Cmd
 
+	switch msg := msg.(type) {
 	case tea.KeyMsg:
 		switch msg.String() {
 		// Down one page
-		case "pgdown":
-			fallthrough
-		case " ": // spacebar
-			fallthrough
-		case "f":
-			m.ViewDown()
-			return m, nil
+		case "pgdown", spacebar, "f":
+			lines := m.ViewDown()
+			if m.HighPerformanceRendering {
+				cmd = ViewDown(m, lines)
+			}
 
 		// Up one page
-		case "pgup":
-			fallthrough
-		case "b":
-			m.ViewUp()
-			return m, nil
+		case "pgup", "b":
+			lines := m.ViewUp()
+			if m.HighPerformanceRendering {
+				cmd = ViewUp(m, lines)
+			}
 
 		// Down half page
-		case "d":
-			m.HalfViewDown()
-			return m, nil
+		case "d", "ctrl+d":
+			lines := m.HalfViewDown()
+			if m.HighPerformanceRendering {
+				cmd = ViewDown(m, lines)
+			}
 
 		// Up half page
-		case "u":
-			m.HalfViewUp()
-			return m, nil
+		case "u", "ctrl+u":
+			lines := m.HalfViewUp()
+			if m.HighPerformanceRendering {
+				cmd = ViewUp(m, lines)
+			}
 
 		// Down one line
-		case "down":
-			fallthrough
-		case "j":
-			m.LineDown(1)
-			return m, nil
+		case "down", "j":
+			lines := m.LineDown(1)
+			if m.HighPerformanceRendering {
+				cmd = ViewDown(m, lines)
+			}
 
 		// Up one line
-		case "up":
-			fallthrough
-		case "k":
-			m.LineUp(1)
-			return m, nil
+		case "up", "k":
+			lines := m.LineUp(1)
+			if m.HighPerformanceRendering {
+				cmd = ViewUp(m, lines)
+			}
+		}
+
+	case tea.MouseMsg:
+		switch msg.Type {
+		case tea.MouseWheelUp:
+			lines := m.LineUp(3)
+			if m.HighPerformanceRendering {
+				cmd = ViewUp(m, lines)
+			}
+
+		case tea.MouseWheelDown:
+			lines := m.LineDown(3)
+			if m.HighPerformanceRendering {
+				cmd = ViewDown(m, lines)
+			}
 		}
 	}
 
-	return m, nil
+	return m, cmd
 }
 
 // VIEW
 
 // View renders the viewport into a string.
 func View(m Model) string {
-	if m.Err != nil {
-		return m.Err.Error()
+	if m.HighPerformanceRendering {
+		// Just send newlines since we're doing to be rendering the actual
+		// content seprately. We still need send something that equals the
+		// height of this view so that the Bubble Tea standard renderer can
+		// position anything below this view properly.
+		return strings.Repeat("\n", m.Height-1)
 	}
 
-	var lines []string
-
-	if len(m.lines) > 0 {
-		top := max(0, m.Y)
-		bottom := min(len(m.lines), m.Y+m.Height)
-		lines = m.lines[top:bottom]
-	}
+	lines := m.visibleLines()
 
 	// Fill empty space with newlines
 	extraLines := ""
@@ -154,6 +376,10 @@ func View(m Model) string {
 
 // ETC
 
+func clamp(v, low, high int) int {
+	return min(high, max(low, v))
+}
+
 func min(a, b int) int {
 	if a < b {
 		return a