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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+
+                            Preamble
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+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -1,4 +1,6 @@
 # objects
 
+[![Go Reference](https://pkg.go.dev/badge/git.tebibyte.media/tomo/objects.svg)](https://pkg.go.dev/git.tebibyte.media/tomo/objects)
+
 Objects contains a standard collection of re-usable objects. All objects in this
 module visually conform to whatever the theme is set to.

button.go

@@ -4,10 +4,16 @@ import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/tomo/theme"
 import "git.tebibyte.media/tomo/tomo/input"
 import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/objects/layouts"
+
+var buttonLayout     = layouts.NewGrid([]bool { true        }, []bool { true })
+var iconButtonLayout = layouts.NewGrid([]bool { false, true }, []bool { true })
 
 // Button is a clickable button.
 type Button struct {
-	tomo.TextBox
+	tomo.ContainerBox
+	label *Label
+	icon  *Icon
 	on struct {
 		click event.FuncBroadcaster
 	}
@@ -15,16 +21,45 @@ type Button struct {
 
 // NewButton creates a new button with the specified text.
 func NewButton (text string) *Button {
-	box := &Button { TextBox: tomo.NewTextBox() }
-	theme.Apply(box, theme.R("objects", "Button"))
-	box.SetText(text)
-	box.SetAlign(tomo.AlignMiddle, tomo.AlignMiddle)
+	box := &Button {
+		ContainerBox: tomo.NewContainerBox(),
+		label:        NewLabel(text),
+	}
+	theme.Apply(box, theme.R("objects", "Button", ""))
+	box.label.SetAlign(tomo.AlignMiddle, tomo.AlignMiddle)
+	box.Add(box.label)
+	box.SetLayout(buttonLayout)
+	
+	box.CaptureDND(true)
+	box.CaptureMouse(true)
+	box.CaptureScroll(true)
+	box.CaptureKeyboard(true)
+	
 	box.OnMouseUp(box.handleMouseUp)
 	box.OnKeyUp(box.handleKeyUp)
 	box.SetFocusable(true)
 	return box
 }
 
+// SetText sets the text of the button's label.
+func (this *Button) SetText (text string) {
+	this.label.SetText(text)
+}
+
+// SetIcon sets an icon for this button.
+// TODO: use tomo.Icon instead, use small size icons
+func (this *Button) SetIcon (icon *Icon) {
+	if this.icon != nil { this.Delete(this.icon) }
+	this.icon = icon
+
+	if this.icon == nil {
+		this.SetLayout(buttonLayout)
+	} else {
+		this.SetLayout(iconButtonLayout)
+		this.Insert(this.icon, this.label)
+	}
+}
+
 // OnClick specifies a function to be called when the button is clicked.
 func (this *Button) OnClick (callback func ()) event.Cookie {
 	return this.on.click.Connect(callback)

container.go

@@ -0,0 +1,39 @@
+package objects
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// Container is an object that can contain other objects. It can be used as a
+// primitive for building more complex layouts. It has two variants: an outer
+// container, and an inner container. The outer container has padding around
+// its edges, whereas the inner container does not. The container will have a
+// corresponding object role variation of either "outer" or "inner".
+type Container struct {
+	tomo.ContainerBox
+}
+
+func newContainer (layout tomo.Layout, children ...tomo.Object) *Container {
+	this := &Container {
+		ContainerBox: tomo.NewContainerBox(),
+	}
+	this.SetLayout(layout)
+	for _, child := range children {
+		this.Add(child)
+	}
+	return this
+}
+
+// NewOuterContainer creates a new container that has padding around it.
+func NewOuterContainer (layout tomo.Layout, children ...tomo.Object) *Container {
+	this := newContainer(layout, children...)
+	theme.Apply(this, theme.R("objects", "Container", "outer"))
+	return this
+}
+
+// NewInnerContainer creates a new container that has no padding around it.
+func NewInnerContainer (layout tomo.Layout, children ...tomo.Object) *Container {
+	this := newContainer(layout, children...)
+	theme.Apply(this, theme.R("objects", "Container", "inner"))
+	return this
+}
+

go.mod

@@ -2,6 +2,6 @@ module git.tebibyte.media/tomo/objects
 
 go 1.20
 
-require git.tebibyte.media/tomo/tomo v0.20.0
+require git.tebibyte.media/tomo/tomo v0.30.0
 
-require golang.org/x/image v0.8.0 // indirect
+require golang.org/x/image v0.11.0 // indirect

go.sum

@@ -1,10 +1,10 @@
-git.tebibyte.media/tomo/tomo v0.20.0 h1:dJJWmCAj/8XtbxjiCkgykP2vNCeP5zuvMEKGChbQ0AI=
-git.tebibyte.media/tomo/tomo v0.20.0/go.mod h1:lTwjpiHbP4UN/kFw+6FwhG600B+PMKVtMOr7wpd5IUY=
+git.tebibyte.media/tomo/tomo v0.30.0 h1:JoTklJ7yFVrzre4AwuKBMwzho9GomC9ySw354wDB4f4=
+git.tebibyte.media/tomo/tomo v0.30.0/go.mod h1:C9EzepS9wjkTJjnZaPBh22YvVPyA4hbBAJVU20Rdmps=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
-golang.org/x/image v0.8.0 h1:agUcRXV/+w6L9ryntYYsF2x9fQTMd4T8fiiYXAVW6Jg=
-golang.org/x/image v0.8.0/go.mod h1:PwLxp3opCYg4WR2WO9P0L6ESnsD6bLTWcw8zanLMVFM=
+golang.org/x/image v0.11.0 h1:ds2RoQvBvYTiJkwpSFDwCcDFNX7DqjL2WsUgTNk0Ooo=
+golang.org/x/image v0.11.0/go.mod h1:bglhjqbqVuEb9e9+eNR45Jfu7D+T4Qan+NhQk8Ck2P8=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
@@ -27,7 +27,7 @@ golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
-golang.org/x/text v0.10.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
+golang.org/x/text v0.12.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=

heading.go

@@ -0,0 +1,23 @@
+package objects
+
+import "fmt"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// Heading is a label that denotes the start of some section of content. It can
+// have a level from 0 to 2, with 0 being the most prominent and 2 being the
+// most subtle. The level is described in the role variation.
+type Heading struct {
+	tomo.TextBox
+}
+
+// NewHeading creates a new section heading. The level can be from 0 to 2.
+func NewHeading (level int, text string) *Label {
+	if level < 0 { level = 0 }
+	if level > 2 { level = 2 }
+	this := &Label { TextBox: tomo.NewTextBox() }
+	theme.Apply(this, theme.R("objects", "Heading", fmt.Sprint(level)))
+	this.SetText(text)
+	return this
+}
+

icon.go

@@ -0,0 +1,42 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/data"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/canvas"
+
+// Icon displays a single icon.
+type Icon struct {
+	tomo.Box
+}
+
+// NewIcon creates a new icon from an icon ID.
+func NewIcon (id theme.Icon, size theme.IconSize) *Icon {
+	this := &Icon {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(this, theme.R("objects", "Icon", size.String()))
+	this.SetTexture(id.Texture(size))
+	return this
+}
+
+// NewMimeIcon creates a new icon from a MIME type.
+func NewMimeIcon (mime data.Mime, size theme.IconSize) *Icon {
+	this := &Icon {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(this, theme.R("objects", "Icon", size.String()))
+	this.SetTexture(theme.MimeIcon(mime, size))
+	return this
+}
+
+func (this *Icon) SetTexture (texture canvas.Texture) {
+	this.Box.SetTexture(texture)
+	if texture == nil {
+		this.SetMinimumSize(image.Pt(0, 0))
+	} else {
+		bounds := texture.Bounds()
+		this.SetMinimumSize(bounds.Max.Sub(bounds.Min))
+	}
+}

input.go

@@ -1,5 +1,6 @@
 package objects
 
+import "image"
 import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/tomo/text"
 import "git.tebibyte.media/tomo/tomo/theme"
@@ -18,11 +19,14 @@ type TextInput struct {
 // NewTextInput creates a new text input containing the specified text.
 func NewTextInput (text string) *TextInput {
 	this := &TextInput { TextBox: tomo.NewTextBox() }
-	theme.Apply(this, theme.R("objects", "TextInput"))
+	theme.Apply(this, theme.R("objects", "TextInput", ""))
+	this.SetAlign(tomo.AlignStart, tomo.AlignMiddle)
 	this.SetText(text)
 	this.SetFocusable(true)
 	this.SetSelectable(true)
+	this.SetOverflow(true, false)
 	this.OnKeyDown(this.handleKeyDown)
+	this.OnScroll(this.handleScroll)
 	return this
 }
 
@@ -50,6 +54,9 @@ func (this *TextInput) handleKeyDown (key input.Key, numpad bool) {
 	sel       := modifiers.Shift
 	changed   := false
 
+	// TODO all this (except editing stuff) really should be moved into the
+	// backend
+
 	switch {
 	case key == input.KeyEnter:
 		this.on.enter.Broadcast()
@@ -88,3 +95,7 @@ func (this *TextInput) handleKeyDown (key input.Key, numpad bool) {
 	this.Select(dot)
 	if changed { this.SetText(string(this.text)) }
 }
+
+func (this *TextInput) handleScroll (x, y float64) {
+	this.ScrollTo(this.ContentBounds().Min.Add(image.Pt(int(x), int(y))))
+}

label.go

@@ -11,8 +11,7 @@ type Label struct {
 // NewLabel creates a new text label.
 func NewLabel (text string) *Label {
 	this := &Label { TextBox: tomo.NewTextBox() }
-	theme.Apply(this, theme.R("objects", "Label"))
+	theme.Apply(this, theme.R("objects", "Label", ""))
 	this.SetText(text)
 	return this
 }
-

layouts/cut.go

@@ -0,0 +1,173 @@
+package layouts
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+
+// Cut is a layout that can be divided into smaller and smaller sections.
+type Cut struct {
+	branches []*Cut
+	expand   []bool
+	vertical bool
+}
+
+// NewCut creates and returns a new Cut layout.
+func NewCut () *Cut {
+	return new(Cut)
+}
+
+// Vertical divides the layout vertically. Sections are specified using
+// booleans. If a section is true, it will expand. If false, it will contract.
+func (this *Cut) Vertical (expand ...bool) {
+	this.expand   = expand
+	this.vertical = true
+	this.fill()
+}
+
+// Horizontal divides the layout horizontally. Sections are specified using
+// booleans. If a section is true, it will expand. If false, it will contract.
+func (this *Cut) Horizontal (expand ...bool) {
+	this.expand   = expand
+	this.vertical = false
+	this.fill()
+}
+
+// At returns the section of this layout at the specified index.
+func (this *Cut) At (index int) *Cut {
+	return this.branches[index]
+}
+
+func (this *Cut) real () bool {
+	return this != nil && this.branches != nil
+}
+
+func (this *Cut) fill () {
+	this.branches = make([]*Cut, len(this.expand))
+	for index := range this.branches {
+		this.branches[index] = new(Cut)
+	}
+}
+
+func (this *Cut) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	size, _ := this.minimumSize(hints, boxes)
+	return size
+}
+
+func (this *Cut) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	this.arrange(hints, boxes)
+}
+
+func (this *Cut) minimumSize (hints tomo.LayoutHints, boxes []tomo.Box) (image.Point, []tomo.Box) {
+	size := image.Point { }
+
+	for index, branch := range this.branches {
+		if len(boxes) == 0 { break }
+
+		var point image.Point
+		if branch.real() {
+			point, boxes = branch.minimumSize(hints, boxes)
+		} else {
+			point = boxes[0].MinimumSize()
+			boxes = boxes[1:]
+		}
+
+		if this.vertical {
+			if point.X > size.X { size.X  = point.X     }
+			if index   > 0      { size.Y += hints.Gap.Y }
+			size.Y += point.Y
+		} else {
+			if point.Y > size.Y { size.Y  = point.Y     }
+			if index   > 0      { size.X += hints.Gap.X }
+			size.X += point.X
+		}
+	}
+
+	return size, boxes
+}
+
+func (this *Cut) arrange (hints tomo.LayoutHints, boxes []tomo.Box) []tomo.Box {
+	nChildren := len(this.branches)
+
+	// collect minimum sizes and physical endpoints
+	var minimums = make([]image.Point,  nChildren)
+	var leaves   = make([]tomo.Box,     nChildren)
+	var nBranches int
+	remaining := boxes
+	for index, branch := range this.branches {
+		if branch.real() {
+			minimums[index], remaining = branch.minimumSize(hints, remaining)
+		} else {
+			if len(remaining) == 0 { break }
+			leaves[index]   = remaining[0]
+			minimums[index] = remaining[0].MinimumSize()
+			remaining       = remaining[1:]
+		}
+		nBranches ++
+	}
+
+	// determine the amount of space to divide among expanding branches
+	gaps := nBranches - 1
+	var freeSpace float64; if this.vertical {
+		freeSpace = float64(hints.Bounds.Dy() - hints.Gap.Y * gaps)
+	} else {
+		freeSpace = float64(hints.Bounds.Dx() - hints.Gap.X * gaps)
+	}
+	var nExpanding float64
+	for index, minimum := range minimums {
+		if this.expand[index] {
+			nExpanding ++
+		} else if this.vertical {
+			freeSpace -= float64(minimum.Y)
+		} else {
+			freeSpace -= float64(minimum.X)
+		}
+	}
+	expandingSize := freeSpace / nExpanding
+
+	// calculate the size and position of branches
+	var bounds = make([]image.Rectangle, nChildren)
+	x := float64(hints.Bounds.Min.X)
+	y := float64(hints.Bounds.Min.Y)
+	for index, minimum := range minimums {
+		// get size along significant axis
+		var size float64; if this.expand[index] {
+			size = expandingSize
+		} else if this.vertical {
+			size = float64(minimum.Y)
+		} else {
+			size = float64(minimum.X)
+		}
+
+		// figure out bounds from size
+		if this.vertical {
+			bounds[index].Max = image.Pt (
+				int(hints.Bounds.Dx()),
+				int(size))
+		} else {
+			bounds[index].Max = image.Pt (
+				int(size),
+				int(hints.Bounds.Dy()))
+		}
+		bounds[index] = bounds[index].Add(image.Pt(int(x), int(y)))
+
+		// move along
+		if this.vertical {
+			y += float64(hints.Gap.Y) + size
+		} else {
+			x += float64(hints.Gap.X) + size
+		}
+	}
+
+	// apply the size and position
+	for index, bound := range bounds {
+		if leaves[index] != nil {
+			leaves[index].SetBounds(bound)
+			boxes = boxes[1:]
+		} else if this.branches[index] != nil {
+			newHints := hints
+			newHints.Bounds = bound
+			boxes = this.branches[index].arrange(newHints, boxes)
+		}
+	}
+	
+	return boxes
+}

layouts/grid.go

@@ -0,0 +1,108 @@
+package layouts
+
+import "math"
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+
+// Grid is a layout that arranges boxes in a grid formation with distinct rows
+// and columns. It is great for creating forms.
+type Grid struct {
+	xExpand []bool
+	yExpand []bool
+}
+
+// NewGrid creates a new grid layout. Rows and columns are specified as slices
+// of booleans, where true means a row or column will expand and false means it
+// will contract. Boxes are laid out left to right, then top to bottom. Boxes
+// that go beyond the lengh of rows will be laid out according to columns, but
+// they will not expand vertically.
+func NewGrid (columns, rows []bool) *Grid {
+	this := &Grid {
+		xExpand: columns,
+		yExpand: rows,
+	}
+	return this
+}
+
+func (this *Grid) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	cols, rows := this.minimums(boxes)
+	size := image.Pt (
+		(len(cols) - 1) * hints.Gap.X,
+		(len(rows) - 1) * hints.Gap.Y)
+	for _, width  := range cols { size.X += width  }
+	for _, height := range rows { size.Y += height }
+	return size
+}
+
+func (this *Grid) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	xExpand := func (index int) bool {
+		return this.xExpand[index]
+	}
+	yExpand := func (index int) bool {
+		if index < len(this.yExpand) { return this.yExpand[index] }
+		return false
+	}
+
+	cols, rows := this.minimums(boxes)
+	expand(hints, cols, hints.Bounds.Dx(), xExpand)
+	expand(hints, rows, hints.Bounds.Dy(), yExpand)
+
+	position := hints.Bounds.Min
+	for index, box := range boxes {
+		col, row := index % len(cols), index / len(cols)
+		box.SetBounds(image.Rectangle {
+			Min: position,
+			Max: position.Add(image.Pt(cols[col], rows[row])),
+		})
+		if col == len(cols) - 1 {
+			position.X = hints.Bounds.Min.X
+			position.Y += rows[row] + hints.Gap.Y
+		} else {
+			position.X += cols[col] + hints.Gap.X
+		}
+	}
+}
+
+func (this *Grid) minimums (boxes []tomo.Box) ([]int, []int) {
+	nCols, nRows := this.dimensions(boxes)
+	cols,  rows  := make([]int, nCols), make([]int, nRows)
+
+	for index, box := range boxes {
+		col, row := index % len(cols), index / len(cols)
+		minimum := box.MinimumSize()
+		if cols[col] < minimum.X {
+			cols[col] = minimum.X
+		}
+		if rows[row] < minimum.Y {
+			rows[row] = minimum.Y
+		}
+	}
+	
+	return cols, rows
+}
+
+func (this *Grid) dimensions (boxes []tomo.Box) (int, int) {
+	return len(this.xExpand), ceilDiv(len(boxes), len(this.xExpand)) 
+}
+
+func expand (hints tomo.LayoutHints, sizes []int, space int, expands func (int) bool) {
+	gaps       := len(sizes) - 1
+	freeSpace  := float64(space - hints.Gap.Y * gaps)
+	nExpanding := 0; for index, minimum := range sizes {
+		if expands(index) {
+			nExpanding ++
+		} else {
+			freeSpace -= float64(minimum)
+		}
+	}
+	expandingSize := freeSpace / float64(nExpanding)
+	for index := range sizes {
+		if expands(index) {
+			sizes[index] = int(expandingSize)
+		}
+	}
+}
+
+func ceilDiv (x, y int) int {
+	return int(math.Ceil(float64(x) / float64(y)))
+}

layouts/layouts.go

@@ -0,0 +1,88 @@
+package layouts
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+
+type Row struct { }
+
+func (Row) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	dot := image.Point { }
+	for _, box := range boxes {
+		minimum := box.MinimumSize()
+		dot.X += minimum.X
+		if dot.Y < minimum.Y {
+			dot.Y = minimum.Y
+		}
+	}
+	dot.X += hints.Gap.X * (len(boxes) - 1)
+	return dot
+}
+
+func (Row) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	// TODO respect alignment value
+	dot := hints.Bounds.Min
+	for index, box := range boxes {
+		if index > 0 { dot.X += hints.Gap.X }
+		minimum := box.MinimumSize()
+		box.SetBounds(image.Rectangle {
+			Min: dot,
+			Max: dot.Add(image.Pt(minimum.X, hints.Bounds.Dy())),
+		})
+		dot.X += minimum.X
+	}
+
+	width  := dot.X - hints.Bounds.Min.X
+	offset := 0
+	
+	switch hints.AlignX {
+	case tomo.AlignMiddle:
+		offset = (hints.Bounds.Dx() - width) / 2
+	case tomo.AlignEnd:
+		offset = hints.Bounds.Dx() - width
+	}
+	for _, box := range boxes {
+		box.SetBounds(box.Bounds().Add(image.Pt(offset, 0)))
+	}
+}
+
+type Column struct { }
+
+func (Column) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	dot := image.Point { }
+	for _, box := range boxes {
+		minimum := box.MinimumSize()
+		dot.Y += minimum.Y
+		if dot.X < minimum.X {
+			dot.X = minimum.X
+		}
+	}
+	dot.Y += hints.Gap.Y * (len(boxes) - 1)
+	return dot
+}
+
+func (Column) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	// TODO respect alignment value
+	dot := hints.Bounds.Min
+	for index, box := range boxes {
+		if index > 0 { dot.Y += hints.Gap.Y }
+		minimum := box.MinimumSize()
+		box.SetBounds(image.Rectangle {
+			Min: dot,
+			Max: dot.Add(image.Pt(hints.Bounds.Dx(), minimum.Y)),
+		})
+		dot.Y += minimum.Y
+	}
+	
+	height := dot.Y - hints.Bounds.Min.Y
+	offset := 0
+	
+	switch hints.AlignY {
+	case tomo.AlignMiddle:
+		offset = (hints.Bounds.Dy() - height) / 2
+	case tomo.AlignEnd:
+		offset = hints.Bounds.Dy() - height
+	}
+	for _, box := range boxes {
+		box.SetBounds(box.Bounds().Add(image.Pt(0, offset)))
+	}
+}

scrollbar.go

@@ -0,0 +1,364 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+
+// Scrollbar is a special type of slider that can control the scroll of any
+// overflowing ContainerBox.
+type Scrollbar struct {
+	tomo.ContainerBox
+	handle     *SliderHandle
+	layout     scrollbarLayout
+	dragging   bool
+	dragOffset image.Point
+
+	linkCookie event.Cookie
+
+	on struct {
+		valueChange event.FuncBroadcaster
+	}
+}
+
+func newScrollbar (orient string) *Scrollbar {
+	this := &Scrollbar {
+		ContainerBox: tomo.NewContainerBox(),
+		handle: &SliderHandle {
+			Box: tomo.NewBox(),
+		},
+		layout: scrollbarLayout {
+			vertical: orient == "vertical",
+		},
+	}
+
+	this.Add(this.handle)
+	this.SetFocusable(true)
+
+	this.CaptureDND(true)
+	this.CaptureMouse(true)
+	this.CaptureScroll(true)
+	this.CaptureKeyboard(true)
+
+	this.OnKeyDown(this.handleKeyDown)
+	this.OnMouseDown(this.handleMouseDown)
+	this.OnMouseUp(this.handleMouseUp)
+	this.OnMouseMove(this.handleMouseMove)
+	this.OnScroll(this.handleScroll)
+	theme.Apply(this.handle, theme.R("objects", "SliderHandle", orient))
+	theme.Apply(this,        theme.R("objects", "Slider", orient))
+	return this
+}
+
+// NewVerticalScrollbar creates a new vertical scrollbar.
+func NewVerticalScrollbar () *Scrollbar {
+	return newScrollbar("vertical")
+}
+
+// NewHorizontalScrollbar creates a new horizontal scrollbar.
+func NewHorizontalScrollbar () *Scrollbar {
+	return newScrollbar("horizontal")
+}
+
+// Link assigns this scrollbar to a ContentBox. Closing the returned cookie will
+// unlink it.
+func (this *Scrollbar) Link (box tomo.ContentBox) event.Cookie {
+	this.layout.linked = box
+	this.linkCookie = this.newLinkCookie (
+		box.OnContentBoundsChange(this.handleLinkedContentBoundsChange))
+	this.SetLayout(this.layout)
+	return this.linkCookie
+}
+
+func (this *Scrollbar) handleLinkedContentBoundsChange () {
+	if this.layout.linked == nil { return }
+	previousValue := this.layout.value
+	trackLength := this.layout.contentLength() - this.layout.viewportLength()
+	if trackLength == 0 {
+		this.layout.value = 0
+	} else {
+		this.layout.value = this.layout.contentPos() / trackLength
+	}
+	this.SetLayout(this.layout)
+	if this.layout.value != previousValue {
+		this.on.valueChange.Broadcast()
+	}
+}
+
+// SetValue sets the value of the scrollbar between 0 and 1, where 0 is scrolled
+// all the way to the left/top, and 1 is scrolled all the way to the
+// right/bottom.
+func (this *Scrollbar) SetValue (value float64) {
+	if this.layout.linked == nil { return }
+	if value > 1 { value = 1 }
+	if value < 0 { value = 0 }
+	
+	trackLength := this.layout.contentLength() - this.layout.viewportLength()
+	position    := trackLength * value
+	point       := this.layout.linked.ContentBounds().Min
+	if this.layout.vertical {
+		point.Y = int(position)
+	} else {
+		point.X = int(position)
+	}
+	this.layout.linked.ScrollTo(point)
+	
+}
+
+// Value returns the value of the scrollbar between 0 and 1 where 0 is scrolled
+// all the way to the left/top, and 1 is scrolled all the way to the
+// right/bottom.
+func (this *Scrollbar) Value () float64 {
+	if this.layout.linked == nil { return 0 }
+	return this.layout.value
+}
+
+// OnValueChange specifies a function to be called when the position of the
+// scrollbar changes.
+func (this *Scrollbar) OnValueChange (callback func ()) event.Cookie {
+	return this.on.valueChange.Connect(callback)
+}
+
+func (this *Scrollbar) handleKeyDown (key input.Key, numpad bool) {
+	var increment float64; if this.layout.vertical {
+		increment = -0.05
+	} else {
+		increment = 0.05
+	}
+
+	switch key {
+	case input.KeyUp, input.KeyLeft:
+		if this.Modifiers().Alt {
+			this.SetValue(0)
+		} else {
+			this.SetValue(this.Value() - increment)
+		}
+	case input.KeyDown, input.KeyRight:
+		if this.Modifiers().Alt {
+			this.SetValue(1)
+		} else {
+			this.SetValue(this.Value() + increment)
+		}
+	case input.KeyHome:
+		this.SetValue(0)
+	case input.KeyEnd:
+		this.SetValue(1)
+	}
+}
+
+func (this *Scrollbar) handleMouseDown (button input.Button) {
+	pointer := this.MousePosition()
+	handle  := this.handle.Bounds()
+
+	within := pointer.In(handle)
+	var above bool; if this.layout.vertical {
+		above = pointer.Y < handle.Min.Y + handle.Dy() / 2
+	} else {
+		above = pointer.X < handle.Min.X + handle.Dx() / 2
+	}
+
+	switch button {
+	case input.ButtonLeft:
+		if within {
+			this.dragging   = true
+			this.dragOffset =
+				pointer.Sub(this.handle.Bounds().Min).
+				Add(this.InnerBounds().Min)
+			this.drag()
+		} else {
+			this.dragOffset = this.fallbackDragOffset()
+			this.dragging   = true
+			this.drag()
+		}
+	case input.ButtonMiddle:
+		if above {
+			this.scrollBy(-this.pageSize())
+		} else {
+			this.scrollBy(this.pageSize())
+		}
+	case input.ButtonRight:
+		if above {
+			this.scrollBy(-this.stepSize())
+		} else {
+			this.scrollBy(this.stepSize())
+		}
+	}
+}
+
+func (this *Scrollbar) handleMouseUp (button input.Button) {
+	if button != input.ButtonLeft || !this.dragging { return }
+	this.dragging = false
+}
+
+func (this *Scrollbar) handleMouseMove () {
+	if !this.dragging { return }
+	this.drag()
+}
+
+func (this *Scrollbar) handleScroll (x, y float64) {
+	if this.layout.linked == nil { return }
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Add(image.Pt(int(x), int(y))))
+}
+
+func (this *Scrollbar) drag () {
+	pointer := this.MousePosition().Sub(this.dragOffset)
+	gutter  := this.InnerBounds()
+	handle  := this.handle.Bounds()
+
+	if this.layout.vertical {
+		this.SetValue (
+			float64(pointer.Y) /
+			float64(gutter.Dy() - handle.Dy()))
+	} else {
+		this.SetValue (
+			float64(pointer.X) /
+			float64(gutter.Dx() - handle.Dx()))
+	}
+}
+
+func (this *Scrollbar) fallbackDragOffset () image.Point {
+	if this.layout.vertical {
+		return this.InnerBounds().Min.
+			Add(image.Pt(0, this.handle.Bounds().Dy() / 2))
+	} else {
+		return this.InnerBounds().Min.
+			Add(image.Pt(this.handle.Bounds().Dx() / 2, 0))
+	}
+}
+
+func (this *Scrollbar) pageSize () int {
+	if this.layout.linked == nil { return 0 }
+	viewport := this.layout.linked.InnerBounds()
+	if this.layout.vertical {
+		return viewport.Dy()
+	} else {
+		return viewport.Dx()
+	}
+}
+
+func (this *Scrollbar) stepSize () int {
+	// FIXME: this should not be hardcoded, need to get base font metrics
+	// from theme somehow. should be (emspace, lineheight)
+	return 16
+}
+
+func (this *Scrollbar) scrollBy (distance int) {
+	if this.layout.linked == nil { return }
+	var vector image.Point; if this.layout.vertical {
+		vector.Y = distance
+	} else {
+		vector.X = distance
+	}
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Add(vector))
+}
+
+type scrollbarCookie struct {
+	owner *Scrollbar
+	subCookies []event.Cookie
+}
+
+func (this *Scrollbar) newLinkCookie (subCookies ...event.Cookie) *scrollbarCookie {
+	return &scrollbarCookie {
+		owner:      this,
+		subCookies: subCookies,
+	}
+}
+
+func (this *scrollbarCookie) Close () {
+	for _, cookie := range this.subCookies {
+		cookie.Close()
+	}
+	this.owner.layout.linked = nil
+	this.owner.SetLayout(this.owner.layout)
+}
+
+type scrollbarLayout struct {
+	vertical bool
+	value    float64
+	linked   tomo.ContentBox
+}
+
+func (scrollbarLayout) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	if len(boxes) != 1 { return image.Pt(0, 0) }
+	return boxes[0].MinimumSize()
+}
+
+func (this scrollbarLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	if len(boxes) != 1 { return }
+	handle := image.Rectangle { Max: boxes[0].MinimumSize() }
+	gutter := hints.Bounds
+
+	var gutterLength float64;
+	var handleMin    float64;
+	if this.vertical {
+		gutterLength = float64(gutter.Dy())
+		handleMin    = float64(handle.Dy())
+	} else {
+		gutterLength = float64(gutter.Dx())
+		handleMin    = float64(handle.Dx())
+	}
+
+	// calculate handle length
+	handleLength := gutterLength * this.viewportContentRatio()
+	if handleLength < handleMin { handleLength = handleMin }
+	if handleLength >= gutterLength {
+		// just hide the handle if it isn't needed.
+		// TODO: we need a way to hide and show boxes, this is janky as
+		// fuck
+		boxes[0].SetBounds(image.Rect(-16, -16, 0, 0))
+		return
+	}
+	if this.vertical {
+		handle.Max.Y = int(handleLength)
+	} else {
+		handle.Max.X = int(handleLength)
+	}
+
+	// calculate handle position
+	handlePosition := (gutterLength - handleLength) * this.value
+	var handleOffset image.Point
+	if this.vertical {
+		handleOffset = image.Pt(0, int(handlePosition))
+	} else {
+		handleOffset = image.Pt(int(handlePosition), 0)
+	}
+	handle = handle.Add(handleOffset).Add(gutter.Min)
+	
+	// place handle
+	boxes[0].SetBounds(handle)
+	
+}
+
+func (this scrollbarLayout) viewportContentRatio () float64 {
+	if this.linked == nil { return 0 }
+	return this.viewportLength() / this.contentLength()
+}
+
+func (this scrollbarLayout) viewportLength () float64 {
+	if this.vertical {
+		return float64(this.linked.InnerBounds().Dy())
+	} else {
+		return float64(this.linked.InnerBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentLength () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Dy())
+	} else {
+		return float64(this.linked.ContentBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentPos () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Min.Y)
+	} else {
+		return float64(this.linked.ContentBounds().Min.X)
+	}
+}

scrollcontainer.go

@@ -0,0 +1,167 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// ScrollSide determines which Scrollbars are active in a ScrollContainer.
+type ScrollSide int; const (
+	ScrollVertical ScrollSide = 1 << iota
+	ScrollHorizontal
+	ScrollBoth = ScrollVertical | ScrollHorizontal
+)
+
+// Horizontal returns true if the side includes a horizontal bar.
+func (sides ScrollSide) Horizontal () bool {
+	return sides & ScrollHorizontal > 0
+}
+
+// Vertical returns true if the side includes a vertical bar.
+func (sides ScrollSide) Vertical () bool {
+	return sides & ScrollVertical > 0
+}
+
+// String returns one of:
+//   - both
+//   - horizontal
+//   - vertical
+//   - none
+func (sides ScrollSide) String () string {
+	switch {
+	case sides.Horizontal() && sides.Vertical(): return "both"
+	case sides.Horizontal():                     return "horizontal"
+	case sides.Vertical():                       return "vertical"
+	default:                                     return "none"
+	}
+}
+
+// ScrollContainer couples a ContentBox with one or two Scrollbars.
+type ScrollContainer struct {
+	tomo.ContainerBox
+	layout *scrollContainerLayout
+
+	horizontalCookie event.Cookie
+	verticalCookie   event.Cookie
+}
+
+// NewScrollContainer creates a new scroll container.
+func NewScrollContainer (sides ScrollSide) *ScrollContainer {
+	this := &ScrollContainer {
+		ContainerBox: tomo.NewContainerBox(),
+		layout:       &scrollContainerLayout { },
+	}
+	if sides.Vertical() {
+		this.layout.vertical = NewVerticalScrollbar()
+		this.Add(this.layout.vertical)
+	}
+	if sides.Horizontal() {
+		this.layout.horizontal = NewHorizontalScrollbar()
+		this.Add(this.layout.horizontal)
+	}
+	this.CaptureScroll(true)
+	this.OnScroll(this.handleScroll)
+	theme.Apply(this, theme.R("objects", "ScrollContainer", sides.String()))
+	this.SetLayout(this.layout)
+	return this
+}
+
+// SetRoot sets the root child of the ScrollContainer. There can only be one at
+// a time, and setting it will remove and unlink the current child if there is
+// one.
+func (this *ScrollContainer) SetRoot (root tomo.ContentBox) {
+	if this.layout.root != nil {
+		// delete root and close cookies
+		this.Delete(this.layout.root)
+		if this.horizontalCookie != nil {
+			this.horizontalCookie.Close()
+			this.horizontalCookie = nil
+		}
+		if this.verticalCookie != nil {
+			this.verticalCookie.Close()
+			this.verticalCookie = nil
+		}
+	}
+	this.layout.root = root
+	if root != nil {
+		// insert root at the beginning (for keynav)
+		switch {
+		case this.layout.vertical != nil:
+			this.Insert(root, this.layout.vertical)
+		case this.layout.horizontal != nil:
+			this.Insert(root, this.layout.horizontal)
+		default:
+			this.Add(root)
+		}
+		
+		// link root and remember cookies
+		if this.layout.horizontal != nil {
+			this.horizontalCookie = this.layout.horizontal.Link(root)
+		}
+		if this.layout.vertical != nil {
+			this.verticalCookie =  this.layout.vertical.Link(root)
+		}
+	}
+}
+
+func (this *ScrollContainer) handleScroll (x, y float64) {
+	if this.layout.root == nil { return }
+	this.layout.root.ScrollTo (
+		this.layout.root.ContentBounds().Min.
+		Add(image.Pt(int(x), int(y))))
+}
+
+type scrollContainerLayout struct {
+	root       tomo.ContentBox
+	horizontal *Scrollbar
+	vertical   *Scrollbar
+}
+
+func (this *scrollContainerLayout) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	var minimum image.Point; if this.root != nil {
+		minimum = this.root.MinimumSize()
+	}
+	if this.horizontal != nil {
+		minimum.Y += this.horizontal.MinimumSize().Y
+	}
+	if this.vertical != nil {
+		minimum.X += this.vertical.MinimumSize().X
+		minimum.Y = max(minimum.Y, this.vertical.MinimumSize().Y)
+	}
+	if this.horizontal != nil {
+		minimum.X = max(minimum.X, this.horizontal.MinimumSize().X)
+	}
+	return minimum
+}
+
+func (this *scrollContainerLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	rootBounds := hints.Bounds
+	if this.horizontal != nil {
+		rootBounds.Max.Y -= this.horizontal.MinimumSize().Y
+	}
+	if this.vertical != nil {
+		rootBounds.Max.X -= this.vertical.MinimumSize().X
+	}
+	if this.root != nil {
+		this.root.SetBounds(rootBounds)
+	}
+	if this.horizontal != nil {
+		this.horizontal.SetBounds(image.Rect (
+			hints.Bounds.Min.X,
+			rootBounds.Max.Y,
+			rootBounds.Max.X,
+			hints.Bounds.Max.Y))
+	}
+	if this.vertical != nil {
+		this.vertical.SetBounds(image.Rect (
+			rootBounds.Max.X,
+			hints.Bounds.Min.Y,
+			hints.Bounds.Max.X,
+			rootBounds.Max.Y))
+	}
+}
+
+func max (x, y int) int {
+	if x > y { return x }
+	return y
+}

separator.go

@@ -0,0 +1,18 @@
+package objects
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// Separator is a line for visually separating elements.
+type Separator struct {
+	tomo.Box
+}
+
+// NewSeparator creates a new separator line.
+func NewSeparator () *Separator {
+	this := &Separator {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(this, theme.R("objects", "Separator", ""))
+	return this
+}

slider.go

@@ -0,0 +1,223 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+
+// Slider is a control that selects a numeric value between 0 and 1.
+type Slider struct {
+	tomo.ContainerBox
+	handle     *SliderHandle
+	layout     sliderLayout
+	dragging   bool
+	dragOffset image.Point
+
+	on struct {
+		valueChange event.FuncBroadcaster
+	}
+}
+
+// SliderHandle is a simple object that serves as a handle for sliders and
+// scrollbars. It is completely inert.
+type SliderHandle struct {
+	tomo.Box
+}
+
+func newSlider (orient string, value float64) *Slider {
+	this := &Slider {
+		ContainerBox: tomo.NewContainerBox(),
+		handle: &SliderHandle {
+			Box: tomo.NewBox(),
+		},
+		layout: sliderLayout {
+			vertical: orient == "vertical",
+		},
+	}
+
+	this.Add(this.handle)
+	this.SetFocusable(true)
+
+	this.CaptureDND(true)
+	this.CaptureMouse(true)
+	this.CaptureScroll(true)
+	this.CaptureKeyboard(true)
+
+	this.SetValue(value)
+	this.OnKeyDown(this.handleKeyDown)
+	this.OnMouseDown(this.handleMouseDown)
+	this.OnMouseUp(this.handleMouseUp)
+	this.OnMouseMove(this.handleMouseMove)
+	theme.Apply(this.handle, theme.R("objects", "SliderHandle", orient))
+	theme.Apply(this,        theme.R("objects", "Slider", orient))
+	return this
+}
+
+// NewVerticalSlider creates a new vertical slider with the specified value.
+func NewVerticalSlider (value float64) *Slider {
+	return newSlider("vertical", value)
+}
+
+// NewHorizontalSlider creates a new horizontal slider with the specified value.
+func NewHorizontalSlider (value float64) *Slider {
+	return newSlider("horizontal", value)
+}
+
+// SetValue sets the value of the slider between 0 and 1.
+func (this *Slider) SetValue (value float64) {
+	if value < 0 { value = 0 }
+	if value > 1 { value = 1 }
+	if value == this.layout.value { return }
+	this.layout.value = value
+	this.SetLayout(this.layout)
+	this.on.valueChange.Broadcast()
+}
+
+// Value returns the value of the slider between 0 and 1.
+func (this *Slider) Value () float64 {
+	return this.layout.value
+}
+
+// OnValueChange specifies a function to be called when the slider's value
+// changes.
+func (this *Slider) OnValueChange (callback func ()) event.Cookie {
+	return this.on.valueChange.Connect(callback)
+}
+
+func (this *Slider) handleKeyDown (key input.Key, numpad bool) {
+	var increment float64; if this.layout.vertical {
+		increment = -0.05
+	} else {
+		increment = 0.05
+	}
+
+	switch key {
+	case input.KeyUp, input.KeyLeft:
+		if this.Modifiers().Alt {
+			this.SetValue(0)
+		} else {
+			this.SetValue(this.Value() - increment)
+		}
+	case input.KeyDown, input.KeyRight:
+		if this.Modifiers().Alt {
+			this.SetValue(1)
+		} else {
+			this.SetValue(this.Value() + increment)
+		}
+	case input.KeyHome:
+		this.SetValue(0)
+	case input.KeyEnd:
+		this.SetValue(1)
+	}
+}
+
+func (this *Slider) handleMouseDown (button input.Button) {
+	pointer := this.MousePosition()
+	handle  := this.handle.Bounds()
+	
+	within := pointer.In(handle)
+	var above bool; if this.layout.vertical {
+		above = pointer.Y < handle.Min.Y + handle.Dy() / 2
+	} else {
+		above = pointer.X < handle.Min.X + handle.Dx() / 2
+	}
+
+	switch button {
+	case input.ButtonLeft:
+		if within {
+			this.dragging   = true
+			this.dragOffset =
+				pointer.Sub(this.handle.Bounds().Min).
+				Add(this.InnerBounds().Min)
+			this.drag()
+		} else {
+			this.dragOffset = this.fallbackDragOffset()
+			this.dragging   = true
+			this.drag()
+		}
+	case input.ButtonMiddle:
+		if above {
+			this.SetValue(0)
+		} else {
+			this.SetValue(1)
+		}
+	case input.ButtonRight:
+		if above {
+			this.SetValue(this.Value() - 0.05)
+		} else {
+			this.SetValue(this.Value() + 0.05)
+		}
+	}
+}
+
+func (this *Slider) handleMouseUp (button input.Button) {
+	if button != input.ButtonLeft || !this.dragging { return }
+	this.dragging = false
+}
+
+func (this *Slider) handleMouseMove () {
+	if !this.dragging { return }
+	this.drag()
+}
+
+func (this *Slider) drag () {
+	pointer := this.MousePosition().Sub(this.dragOffset)
+	gutter  := this.InnerBounds()
+	handle  := this.handle.Bounds()
+
+	if this.layout.vertical {
+		this.SetValue (
+			1 -
+			float64(pointer.Y) /
+			float64(gutter.Dy() - handle.Dy()))
+	} else {
+		this.SetValue (
+			float64(pointer.X) /
+			float64(gutter.Dx() - handle.Dx()))
+	}
+}
+
+func (this *Slider) fallbackDragOffset () image.Point {
+	if this.layout.vertical {
+		return this.InnerBounds().Min.
+			Add(image.Pt(0, this.handle.Bounds().Dy() / 2))
+	} else {
+		return this.InnerBounds().Min.
+			Add(image.Pt(this.handle.Bounds().Dx() / 2, 0))
+	}
+}
+
+type sliderLayout struct {
+	vertical bool
+	value    float64
+}
+
+func (sliderLayout) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	if len(boxes) != 1 { return image.Pt(0, 0) }
+	return boxes[0].MinimumSize()
+}
+
+func (this sliderLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	if len(boxes) != 1 { return }
+	handle := image.Rectangle { Max: boxes[0].MinimumSize() }
+	gutter := hints.Bounds
+
+	if this.vertical {
+		height := gutter.Dy() - handle.Dy()
+		offset := int(float64(height) * (1 - this.value))
+		handle.Max.X = gutter.Dx()
+		boxes[0].SetBounds (
+			handle.
+			Add(image.Pt(0, offset)).
+			Add(gutter.Min))
+	} else {
+		width  := gutter.Dx() - handle.Dx()
+		offset := int(float64(width) * this.value)
+		handle.Max.Y = gutter.Dy()
+		boxes[0].SetBounds (
+			handle.
+			Add(image.Pt(offset, 0)).
+			Add(gutter.Min))
+	}
+}

textview.go

@@ -0,0 +1,27 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// TextView is an area for displaying a large amount of multi-line text.
+type TextView struct {
+	tomo.TextBox
+}
+
+// NewTextView creates a new text view.
+func NewTextView (text string) *TextView {
+	this := &TextView { TextBox: tomo.NewTextBox() }
+	theme.Apply(this, theme.R("objects", "TextView", ""))
+	this.SetFocusable(true)
+	this.SetSelectable(true)
+	this.SetText(text)
+	this.SetOverflow(false, true)
+	this.SetWrap(true)
+	this.OnScroll(this.handleScroll)
+	return this
+}
+
+func (this *TextView) handleScroll (x, y float64) {
+	this.ScrollTo(this.ContentBounds().Min.Add(image.Pt(int(x), int(y))))
+}