Upgrade x/image

backend.go

@@ -4,18 +4,26 @@ import "sort"
 import "image"
 import "errors"
 
+// Backend is any Tomo implementation. Backends handle window creation, layout,
+// rendering, and events so that there can be as many platform-specific
+// optimizations as possible.
 type Backend interface {
+	// These methods create new objects. The backend must reject any object
+	// that was not made by it.
 	NewWindow       (image.Rectangle) (MainWindow, error)
 	NewBox          () Box
 	NewTextBox      () TextBox
 	NewCanvasBox    () CanvasBox
 	NewContainerBox () ContainerBox
 
+	// Run runs the event loop until Stop() is called, or the backend
+	// experiences a fatal error.
+	Run () error
+	
 	// Stop must unblock run.
-	Run  () error
 	Stop ()
 
-	// Do performs a callback function in the main thread as soon as
+	// Do performs a callback function in the event loop thread as soon as
 	// possible. This method must be safe to call concurrently.
 	Do (func ())
 }

canvas/canvas.go

@@ -8,24 +8,24 @@ import "image/color"
 
 // Cap represents a stroke cap type.
 type Cap int; const (
-	CapButt Cap = iota
-	CapRound
-	CapSquare
+	CapButt Cap = iota // Square cap that ends at the point
+	CapRound           // Round cap that surrounds the point
+	CapSquare          // square cap that surrounds the point
 )
 
 // Joint represents a stroke joint type.
 type Joint int; const (
-	JointRount Joint = iota
-	JointSharp
-	JointMiter
+	JointRount Joint = iota // Rounded joint
+	JointSharp              // Sharp joint
+	JointMiter              // Clipped/beveled joint
 )
 
 // StrokeAlign determines whether a stroke is drawn inside, outside, or on a
 // path.
 type StrokeAlign int; const (
-	StrokeAlignCenter StrokeAlign = iota
-	StrokeAlignInner
-	StrokeAlignOuter
+	StrokeAlignCenter StrokeAlign = iota // Centered on the path
+	StrokeAlignInner                     // Inset into the path
+	StrokeAlignOuter                     // Outset around the path
 )
 
 // Pen represents a drawing context that is linked to a canvas. Each canvas can
@@ -44,9 +44,8 @@ type Pen interface {
 	StrokeWeight (int)         // how thick the stroke is
 	StrokeAlign  (StrokeAlign) // where the stroke is drawn
 
-	// set the stroke/fill to a solid color
-	Stroke (color.Color)
-	Fill   (color.Color)
+	Stroke (color.Color) // Sets the stroke to a solid color
+	Fill   (color.Color) // Sets the fill to a solid color
 }
 
 // Canvas is an image that supports drawing paths.
@@ -62,6 +61,7 @@ type Canvas interface {
 
 // Drawer is an object that can draw to a canvas.
 type Drawer interface {
+	// Draw draws to the given canvas.
 	Draw (Canvas)
 }
 

canvas/shatter.go

@@ -0,0 +1,96 @@
+package canvas
+
+import "image"
+
+// Shatter takes in a bounding rectangle, and several rectangles to be
+// subtracted from it. It returns a slice of rectangles that tile together to
+// make up the difference between them. This is intended to be used for figuring
+// out which areas of a container box's background are covered by other boxes so
+// it doesn't waste CPU cycles drawing to those areas.
+func Shatter (
+	glass image.Rectangle,
+	rocks ...image.Rectangle,
+) (
+	tiles []image.Rectangle,
+) {
+	// in this function, the metaphor of throwing several rocks at a sheet
+	// of glass is used to illustrate the concept.
+
+	tiles = []image.Rectangle { glass }
+	for _, rock := range rocks {
+		
+		// check each tile to see if the rock has collided with it
+		tileLen := len(tiles)
+		for tileIndex := 0; tileIndex < tileLen; tileIndex ++ {
+			tile := tiles[tileIndex]
+			if !rock.Overlaps(tile) { continue }
+			newTiles, n := shatterOnce(tile, rock)
+			if n > 0 {
+				// the tile was shattered into one or more sub
+				// tiles
+				tiles[tileIndex] = newTiles[0]
+				tiles = append(tiles, newTiles[1:n]...)
+			} else {
+				// the tile was entirely obscured by the rock
+				// and must be wholly removed
+				tiles = remove(tiles, tileIndex)
+				tileIndex --
+				tileLen --
+			}
+		}
+	}
+	return
+}
+
+func shatterOnce (glass, rock image.Rectangle) (tiles [4]image.Rectangle, n int) {
+	rock = rock.Intersect(glass)
+
+	// |'''''''''''|
+	// |           |
+	// |###|'''|   |
+	// |###|___|   |
+	// |           |
+	// |___________|
+	if rock.Min.X > glass.Min.X { tiles[n] = image.Rect (
+		glass.Min.X, rock.Min.Y,
+		rock.Min.X,  rock.Max.Y,
+	); n ++ }
+	
+	// |'''''''''''|
+	// |           |
+	// |   |'''|###|
+	// |   |___|###|
+	// |           |
+	// |___________|
+	if rock.Max.X < glass.Max.X { tiles[n] = image.Rect (
+		rock.Max.X,  rock.Min.Y,
+		glass.Max.X, rock.Max.Y,
+	); n ++ }
+	
+	// |###########|
+	// |###########|
+	// |   |'''|   |
+	// |   |___|   |
+	// |           |
+	// |___________|
+	if rock.Min.Y > glass.Min.Y { tiles[n] = image.Rect (
+		glass.Min.X, glass.Min.Y,
+		glass.Max.X, rock.Min.Y,
+	); n ++ }
+	
+	// |'''''''''''|
+	// |           |
+	// |   |'''|   |
+	// |   |___|   |
+	// |###########|
+	// |###########|
+	if rock.Max.Y < glass.Max.Y { tiles[n] = image.Rect (
+		glass.Min.X, rock.Max.Y,
+		glass.Max.X, glass.Max.Y,
+	); n ++ }
+	return
+}
+
+func remove[ELEMENT any] (slice []ELEMENT, s int) []ELEMENT {
+    return append(slice[:s], slice[s + 1:]...)
+}

data/data.go

@@ -27,7 +27,10 @@ func (mime Mime) String () string {
 	return mime.Type + "/" + mime.Subtype
 }
 
+// MimePlain returns the MIME type of plain text.
 func MimePlain () Mime { return Mime { "text", "plain"    } }
+
+// MimeFile returns the MIME type of a file path/URI.
 func MimeFile  () Mime { return Mime { "text", "uri-list" } }
 
 type byteReadCloser struct { *bytes.Reader }

event/event.go

@@ -9,46 +9,77 @@ type Cookie interface {
 	Close ()
 }
 
-// Broadcaster manages event listeners
-type Broadcaster struct {
+// Broadcaster manages event listeners.
+type Broadcaster[L any] struct {
 	lastID    int
-	listeners map[int] func ()
+	listeners map[int] L
 }
 
 // Connect adds a new listener to the broadcaster and returns a corresponding
 // cookie.
-func (broadcaster *Broadcaster) Connect (listener func ()) Cookie {
-	if listener == nil { return nil }
-
-	if broadcaster.listeners == nil {
-		broadcaster.listeners = make(map[int] func ())
-	}
+func (broadcaster *Broadcaster[L]) Connect (listener L) Cookie {
+	broadcaster.ensure()
 	
 	cookie := broadcaster.newCookie()
 	broadcaster.listeners[cookie.id] = listener
 	return cookie
 }
 
-// Broadcast runs all event listeners at once.
-func (broadcaster *Broadcaster)  Broadcast () {
-	for _, listener := range broadcaster.listeners {
-		listener()
-	}
+// Listeners returns a map of all connected listeners.
+func (broadcaster *Broadcaster[L]) Listeners () map[int] L {
+	broadcaster.ensure()
+	return broadcaster.listeners
 }
 
-func (broadcaster *Broadcaster) newCookie () cookie {
+func (broadcaster *Broadcaster[L]) newCookie () cookie[L] {
 	broadcaster.lastID ++
-	return cookie {
+	return cookie[L] {
 		id:          broadcaster.lastID,
 		broadcaster: broadcaster,
 	}
 }
 
-type cookie struct {
-	id int
-	broadcaster *Broadcaster
+func (broadcaster *Broadcaster[L]) ensure () {
+	if broadcaster.listeners == nil {
+		broadcaster.listeners = make(map[int] L)
+	}
 }
 
-func (cookie cookie) Close () {
+// NoCookie is a cookie that does nothing when closed.
+type NoCookie struct { }
+func (NoCookie) Close () { }
+
+type cookie[L any] struct {
+	id int
+	broadcaster *Broadcaster[L]
+}
+
+func (cookie cookie[L]) Close () {
 	delete(cookie.broadcaster.listeners, cookie.id)
 }
+
+// FuncBroadcaster is a broadcaster that manages functions with no arguments.
+type FuncBroadcaster struct {
+	Broadcaster[func ()]
+}
+
+// Broadcast calls all connected listener funcs.
+func (broadcaster *FuncBroadcaster) Broadcast () {
+	for _, listener := range broadcaster.Listeners() {
+		listener()
+	}
+}
+
+type multiCookie []Cookie
+
+// MultiCookie creates a single cookie that, when closed, closes a list of other
+// cookies.
+func MultiCookie (cookies ...Cookie) Cookie {
+	return multiCookie(cookies)
+}
+
+func (cookies multiCookie) Close () {
+	for _, cookie := range cookies {
+		cookie.Close()
+	}
+}

go.mod

@@ -2,4 +2,4 @@ module git.tebibyte.media/tomo/tomo
 
 go 1.20
 
-require golang.org/x/image v0.8.0
+require golang.org/x/image v0.11.0

go.sum

@@ -3,6 +3,8 @@ golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACk
 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=
@@ -26,6 +28,7 @@ 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=

input/input.go

@@ -59,6 +59,18 @@ const (
 	KeyF10 Key = 138
 	KeyF11 Key = 139
 	KeyF12 Key = 140
+	KeyF13 Key = 141
+	KeyF14 Key = 142
+	KeyF15 Key = 143
+	KeyF16 Key = 144
+	KeyF17 Key = 145
+	KeyF18 Key = 146
+	KeyF19 Key = 147
+	KeyF20 Key = 148
+	KeyF21 Key = 149
+	KeyF22 Key = 150
+	KeyF23 Key = 151
+	KeyF24 Key = 152
 )
 
 // Button represents a mouse button.

object.go

@@ -3,19 +3,97 @@ package tomo
 import "image"
 import "image/color"
 import "golang.org/x/image/font"
+import "git.tebibyte.media/tomo/tomo/text"
 import "git.tebibyte.media/tomo/tomo/data"
 import "git.tebibyte.media/tomo/tomo/event"
 import "git.tebibyte.media/tomo/tomo/input"
 import "git.tebibyte.media/tomo/tomo/canvas"
 
-type Inset [4]int
-type Gap   image.Point
+// Side represents one side of a rectangle.
+type Side int; const (
+	SideTop Side = iota
+	SideRight
+	SideBottom
+	SideLeft
+)
 
+// Inset represents a rectangle inset that can have a different value for each
+// side.
+type Inset [4]int
+
+// I allows you to create an inset in a CSS-ish way:
+//
+//   - One argument: all sides are set to this value
+//   - Two arguments: the top and bottom sides are set to the first value, and
+//     the left and right sides are set to the second value.
+//   - Three arguments: the top side is set by the first value, the left and
+//     right sides are set by the second vaue, and the bottom side is set by the
+//     third value.
+//   - Four arguments: each value corresponds to a side.
+//
+// This function will panic if an argument count that isn't one of these is
+// given.
+func I (sides ...int) Inset {
+	switch len(sides) {
+	case 1: return Inset { sides[0], sides[0], sides[0], sides[0] }
+	case 2: return Inset { sides[0], sides[1], sides[0], sides[1] }
+	case 3: return Inset { sides[0], sides[1], sides[2], sides[1] }
+	case 4: return Inset { sides[0], sides[1], sides[2], sides[3] }
+	default: panic("I: illegal argument count.")
+	}
+}
+
+// Apply returns the given rectangle, shrunk on all four sides by the given
+// inset. If a measurment of the inset is negative, that side will instead be
+// expanded outward. If the rectangle's dimensions cannot be reduced any
+// further, an empty rectangle near its center will be returned.
+func (inset Inset) Apply (bigger image.Rectangle) (smaller image.Rectangle) {
+	smaller = bigger
+	if smaller.Dx() < inset[3] + inset[1] {
+		smaller.Min.X = (smaller.Min.X + smaller.Max.X) / 2
+		smaller.Max.X = smaller.Min.X
+	} else {
+		smaller.Min.X += inset[3]
+		smaller.Max.X -= inset[1]
+	}
+
+	if smaller.Dy() < inset[0] + inset[2] {
+		smaller.Min.Y = (smaller.Min.Y + smaller.Max.Y) / 2
+		smaller.Max.Y = smaller.Min.Y
+	} else {
+		smaller.Min.Y += inset[0]
+		smaller.Max.Y -= inset[2]
+	}
+	return
+}
+
+// Inverse returns a negated version of the inset.
+func (inset Inset) Inverse () (prime Inset) {
+	return Inset {
+		inset[0] * -1,
+		inset[1] * -1,
+		inset[2] * -1,
+		inset[3] * -1,
+	}
+}
+
+// Horizontal returns the sum of SideRight and SideLeft.
+func (inset Inset) Horizontal () int {
+	return inset[SideRight] + inset[SideLeft]
+}
+
+// Vertical returns the sum of SideTop and SideBottom.
+func (inset Inset) Vertical () int {
+	return inset[SideTop] + inset[SideBottom]
+}
+
+// Border represents a single border of a box.
 type Border struct {
 	Width Inset
 	Color [4]color.Color
 }
 
+// Align lists basic alignment types.
 type Align int; const (
 	AlignStart Align = iota // similar to left-aligned text
 	AlignMiddle             // similar to center-aligned text
@@ -23,29 +101,76 @@ type Align int; const (
 	AlignEven               // similar to justified text
 )
 
+// Object is any obscreen object. Each object must be linked to a box, even if
+// it is that box.
 type Object interface {
 	Box () Box
 }
 
+// Box is a basic styled box.
 type Box interface {
 	Object
+
+	// Window returns the Window this Box is a part of.
+	Window         () Window
+	// Bounds returns the outer bounding rectangle of the Box relative to
+	// the Window.
 	Bounds         () image.Rectangle
+	// InnerBounds returns the inner bounding rectangle of the box. It is
+	// the value of Bounds inset by the Box's border and padding.
 	InnerBounds    () image.Rectangle
+	// MinimumSize returns the minimum width and height this Box's bounds
+	// can be set to. This will return the value of whichever of these is
+	// greater:
+	//   - The size as set by SetMinimumSize
+	//   - The size taken up by the Box's border and padding. If there is
+	//     internal content that does not overflow, the size of that is also
+	//     taken into account here.
+	MinimumSize    () image.Point
+	// SetBounds sets the bounding rectangle of this Box relative to the
+	// Window.
 	SetBounds      (image.Rectangle)
+	// SetColor sets the background color of this Box.
 	SetColor       (color.Color)
+	// SetBorder sets the Border(s) of the box. The first Border will be the
+	// most outset, and the last Border will be the most inset.
 	SetBorder      (...Border)
-	SetMinimumSize (int, int)
+	// SetMinimumSize sets the minimum width and height of the box, as
+	// described in MinimumSize.
+	SetMinimumSize (image.Point)
+	// SetPadding sets the padding between the Box's innermost Border and
+	// its content.
 	SetPadding     (Inset)
 
+	// SetDNDData sets the data that will be picked up if this Box is
+	// dragged. If this is nil (which is the default), this Box will not be
+	// picked up.
 	SetDNDData   (data.Data)
+	// SetDNDAccept sets the type of data that can be dropped onto this Box.
+	// If this is nil (which is the default), this Box will reject all
+	// drops.
 	SetDNDAccept (...data.Mime)
+	// SetFocused sets whether or not this Box has keyboard focus. If set to
+	// true, this method will steal focus away from whichever Object
+	// currently has focus.
 	SetFocused   (bool)
+	// SetFocusable sets whether or not this Box can receive keyboard focus.
+	// If set to false and the Box is already focused. the focus is removed.
 	SetFocusable (bool)
-	
-	Focused       () bool
-	Modifiers     (func ()) input.Modifiers
-	MousePosition (func ()) image.Point
 
+	// Focused returns whether or not this Box has keyboard focus.
+	Focused       () bool
+	// Modifiers returns which modifier keys on the keyboard are currently
+	// being held down.
+	Modifiers     () input.Modifiers
+	// MousePosition returns the position of the mouse pointer relative to
+	// the Window.
+	MousePosition () image.Point
+
+	// These are event subscription functions that allow callbacks to be
+	// connected to particular events. Multiple callbacks may be connected
+	// to the same event at once. Callbacks can be removed by closing the
+	// returned cookie.
 	OnFocusEnter  (func ()) event.Cookie
 	OnFocusLeave  (func ()) event.Cookie
 	OnDNDEnter    (func ()) event.Cookie
@@ -59,58 +184,172 @@ type Box interface {
 	OnScroll      (func (deltaX, deltaY float64)) event.Cookie
 	OnKeyDown     (func (key input.Key, numberPad bool)) event.Cookie
 	OnKeyUp       (func (key input.Key, numberPad bool)) event.Cookie
-
-	ContentBounds         () image.Rectangle
-	ScrollTo              (image.Point)
-	OnContentBoundsChange (func ()) event.Cookie
-}
-
-type TextBox interface {
-	Box
-	SetTextColor (color.Color)
-	SetFace      (font.Face)
-	SetHAlign    (Align)
-	SetVAlign    (Align)
 }
 
+// CanvasBox is a box that can be drawn to.
 type CanvasBox interface {
 	Box
+
+	// SetDrawer sets the Drawer that will be called upon to draw the Box's
+	// content when it is invalidated.
 	SetDrawer  (canvas.Drawer)
+
+	// Invalidate causes the Box's area to be redrawn at the end of the
+	// event cycle, even if it wouldn't be otherwise.
 	Invalidate ()
 }
 
-type ContainerBox interface {
+// ContentBox is an abstract box that has some kind of content. Its only purpose
+// is to be embedded into TextBox and ContainerBox.
+type ContentBox interface {
 	Box
-	SetGap    (Gap)
-	Add       (Object)
-	Delete    (Object)
-	Insert    (child Object, before Object)
-	Clear     ()
-	Length    () int
-	At        (int) Object
-	SetLayout (Layout)
+
+	// SetOverflow sets whether or not the Box's content overflows
+	// horizontally and vertically. Overflowing content is clipped to the
+	// bounds of the Box inset by all Borders (but not padding).
+	SetOverflow           (horizontal, vertical bool)
+	// SetAlign sets how the Box's content is distributed horizontally and
+	// vertically.
+	SetAlign              (x, y Align)
+	// ContentBounds returns the bounds of the inner content of the Box
+	// relative to the window.
+	ContentBounds         () image.Rectangle
+	// ScrollTo shifts the origin of the Box's content to the origin of the
+	// Box's InnerBounds, offset by the given point.
+	ScrollTo              (image.Point)
+	// OnContentBoundsChange specifies a function to be called when the
+	// Box's ContentBounds or InnerBounds changes.
+	OnContentBoundsChange (func ()) event.Cookie
 }
 
+// TextBox is a box that contains text content.
+type TextBox interface {
+	ContentBox
+
+	// SetText sets the text content of the Box.
+	SetText       (string)
+	// SetTextColor sets the text color.
+	SetTextColor  (color.Color)
+	// SetFace sets the font face text is rendered in.
+	SetFace       (font.Face)
+	// SetWrap sets whether or not the text wraps.
+	SetWrap       (bool)
+
+	// SetSelectable sets whether or not the text content can be
+	// highlighted/selected.
+	SetSelectable (bool)
+	// SetDotColor sets the highlight color of selected text.
+	SetDotColor   (color.Color)
+	// Select sets the text cursor or selection.
+	Select        (text.Dot)
+	// Dot returns the text cursor or selection.
+	Dot           () text.Dot
+	// OnDotChange specifies a function to be called when the text cursor or
+	// selection changes.
+	OnDotChange   (func ()) event.Cookie
+}
+
+// ContentBox is a box that can contain child Objects. It arranges them
+// according to a layout rule.
+type ContainerBox interface {
+	ContentBox
+
+	// SetPropagateEvents specifies whether or not child Objects will
+	// receive user input events. It is true by default. If it is false, all
+	// user input that would otherwise be directed to a child Box is
+	// directed to this Box.
+	SetPropagateEvents (bool)
+	// SetGap sets the gap between child Objects.
+	SetGap             (image.Point)
+	// Add appends a child Object.
+	Add                (Object)
+	// Delete removes a child Object, if it is a child of this Box.
+	Delete             (Object)
+	// Insert inserts a child Object before a specified Object. If the
+	// before Object is nil or is not contained within this Box, the
+	// inserted Object is appended.
+	Insert             (child Object, before Object)
+	// Clear removes all child Objects.
+	Clear              ()
+	// Length returns the amount of child objects.
+	Length             () int
+	// At returns the child Object at the specified index.
+	At                 (int) Object
+	// SetLayout sets the layout of this Box. Child Objects will be
+	// positioned according to it.
+	SetLayout          (Layout)
+}
+
+// LayoutHints are passed to a layout to tell it how to arrange child boxes.
+type LayoutHints struct {
+	// Bounds is the bounding rectangle that children should be placed
+	// within. Any padding values are already applied.
+	Bounds image.Rectangle
+	// OverflowX and OverflowY control wether child Boxes may be positioned
+	// outside of Bounds.
+	OverflowX bool
+	OverflowY bool
+	// AlignX and AlignY control how child Boxes are aligned horizontally
+	// and vertically. The effect of this may vary depending on the Layout.
+	AlignX    Align
+	AlignY    Align
+	// Gap controls the amount of horizontal and vertical spacing in-between
+	// child Boxes.
+	Gap image.Point
+}
+
+// A Layout can be given to a ContainerBox to arrange child objects.
+type Layout interface {
+	// MinimumSize returns the minimum width and height of
+	// LayoutHints.Bounds needed to properly lay out all child Boxes.
+	MinimumSize (LayoutHints, []Box) image.Point
+	// Arrange arranges child boxes according to the given LayoutHints.
+	Arrange     (LayoutHints, []Box)
+}
+
+// Window is an operating system window. It can contain one object.
 type Window interface {
+	// SetRoot sets the root child of the window. There can only be one at
+	// a time, and setting it will remove the current child if there is one.
 	SetRoot  (Object)
+	// SetTitle sets the title of the window.
 	SetTitle (string)
-	SetIcon  (sizes []image.Image)
-	NewMenu  (image.Rectangle) (Window, error)
-	NewModal (image.Rectangle) (Window, error)
+	// SetIcon sets the icon of the window. When multiple icon sizes are
+	// provided, the best fitting one is chosen for display.
+	SetIcon  (... image.Image)
+	// Widget returns a window representing a smaller iconified form of this
+	// window. How exactly this window is used depends on the platform.
+	// Subsequent calls to this method on the same window will return the
+	// same window object.
 	Widget   () (Window, error)
+	// NewMenu creates a new menu window. This window is undecorated and
+	// will close once the user clicks outside of it.
+	NewMenu  (image.Rectangle) (Window, error)
+	// NewModal creates a new modal window that blocks all input to this
+	// window until it is closed.
+	NewModal (image.Rectangle) (Window, error)
+	// Copy copies data to the clipboard.
 	Copy     (data.Data)
+	// Paste reads data from the clipboard. When the data is available or an
+	// error has occurred, the provided function will be called.
 	Paste    (callback func (data.Data, error), accept ...data.Mime)
+	// Show shows the window.
 	Show     ()
+	// Hide hides the window.
 	Hide     ()
+	// Close closes the window.
 	Close    ()
+	// OnClose specifies a function to be called when the window is closed.
 	OnClose  (func ()) event.Cookie
 }
 
+// MainWindow is a top-level operating system window.
 type MainWindow interface {
 	Window
+
+	// NewChild creates a new window that is semantically a child of this
+	// window. It does not actually reside within this window, but it may be
+	// linked to it via some other means. This is intended for things like
+	// toolboxes and tear-off menus.
 	NewChild (image.Rectangle) (Window, error)
 }
-
-type Layout interface {
-	Arrange (image.Rectangle, Gap, []Box)
-}

text/text.go

@@ -0,0 +1,248 @@
+package text
+
+import "unicode"
+
+// Dot represents a cursor or text selection. It has a start and end position,
+// referring to where the user began and ended the selection respectively.
+type Dot struct { Start, End int }
+
+// EmptyDot returns a zero-width dot at the specified position.
+func EmptyDot (position int) Dot {
+	return Dot { position, position }
+}
+
+// Canon places the lesser value at the start, and the greater value at the end.
+// Note that a canonized dot does not in all cases correspond directly to the
+// original, because there is a semantic value to the start and end positions.
+func (dot Dot) Canon () Dot {
+	if dot.Start > dot.End {
+		return Dot { dot.End, dot.Start }
+	} else {
+		return dot
+	}
+}
+
+// Empty returns whether or not the 
+func (dot Dot) Empty () bool {
+	return dot.Start == dot.End
+}
+
+// Add shifts the dot to the right by the specified amount.
+func (dot Dot) Add (delta int) Dot {
+	return Dot {
+		dot.Start + delta,
+		dot.End   + delta,
+	}
+}
+
+// Sub shifts the dot to the left by the specified amount.
+func (dot Dot) Sub (delta int) Dot {
+	return Dot {
+		dot.Start - delta,
+		dot.End   - delta,
+	}
+}
+
+// Constrain constrains the dot's start and end from zero to length (inclusive).
+func (dot Dot) Constrain (length int) Dot {
+	if dot.Start < 0      { dot.Start = 0      }
+	if dot.Start > length { dot.Start = length }
+	if dot.End   < 0      { dot.End   = 0      }
+	if dot.End   > length { dot.End   = length }
+	return dot
+}
+
+// Width returns how many runes the dot spans.
+func (dot Dot) Width () int {
+	dot = dot.Canon()
+	return dot.End - dot.Start
+}
+
+// Slice returns the subset of text that the dot covers.
+func (dot Dot) Slice (text []rune) []rune {
+	dot = dot.Canon().Constrain(len(text))
+	return text[dot.Start:dot.End]
+}
+
+// WordToLeft returns how far away to the left the next word boundary is from a
+// given position.
+func WordToLeft (text []rune, position int) (length int) {
+	if position < 1 { return }
+	if position > len(text) { position = len(text) }
+
+	index := position - 1
+	for index >= 0 && unicode.IsSpace(text[index]) {
+		length ++
+		index --
+	}
+	for index >= 0 && !unicode.IsSpace(text[index]) {
+		length ++
+		index --
+	}
+	return
+}
+
+// WordToRight returns how far away to the right the next word boundary is from
+// a given position.
+func WordToRight (text []rune, position int) (length int) {
+	if position < 0 { return }
+	if position > len(text) { position = len(text) }
+
+	index := position
+	for index < len(text) && unicode.IsSpace(text[index]) {
+		length ++
+		index ++
+	}
+	for index < len(text) && !unicode.IsSpace(text[index]) {
+		length ++
+		index ++
+	}
+	return
+}
+
+// WordAround returns a dot that surrounds the word at the specified position.
+func WordAround (text []rune, position int) (around Dot) {
+	return Dot {
+		position - WordToLeft(text, position),
+		position + WordToRight(text, position),
+	}
+}
+
+// Backspace deletes the rune to the left of the dot. If word is true, it
+// deletes up until the next word boundary on the left. If the dot is non-empty,
+// it deletes the text inside of the dot.
+func Backspace (text []rune, dot Dot, word bool) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		distance := 1
+		if word {
+			distance = WordToLeft(text, dot.End)
+		}
+		result = append (
+			result,
+			text[:dot.Sub(distance).Constrain(len(text)).End]...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Sub(distance).Start)
+		return
+	} else {
+		return Delete(text, dot, word)
+	}
+}
+
+// Delete deletes the rune to the right of the dot. If word is true, it deletes
+// up until the next word boundary on the right. If the dot is non-empty, it
+// deletes the text inside of the dot.
+func Delete (text []rune, dot Dot, word bool) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		distance := 1
+		if word {
+			distance = WordToRight(text, dot.End)
+		}
+		result = append(result, text[:dot.End]...)
+		result = append (
+			result,
+			text[dot.Add(distance).Constrain(len(text)).End:]...)
+		moved = dot
+		return	
+	} else {
+		dot = dot.Canon()
+		result = append(result, text[:dot.Start]...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Start)
+		return
+	}
+}
+
+// Lift removes the section of text inside of the dot, and returns a copy of it.
+func Lift (text []rune, dot Dot) (result []rune, moved Dot, lifted []rune) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		moved = dot
+		return
+	}
+
+	dot = dot.Canon()
+	lifted = make([]rune, dot.Width())
+	copy(lifted, dot.Slice(text))
+	result = append(result, text[:dot.Start]...)
+	result = append(result, text[dot.End:]...)
+	moved = EmptyDot(dot.Start)
+	return
+}
+
+// Type inserts one of more runes into the text at the dot position. If the dot
+// is non-empty, it replaces the text inside of the dot with the new runes.
+func Type (text []rune, dot Dot, characters ...rune) (result []rune, moved Dot) {
+	dot = dot.Constrain(len(text))
+	if dot.Empty() {
+		result = append(result, text[:dot.End]...)
+		result = append(result, characters...)
+		if dot.End < len(text) {
+			result = append(result, text[dot.End:]...)
+		}
+		moved = EmptyDot(dot.Add(len(characters)).End)
+		return
+	} else {
+		dot = dot.Canon()
+		result = append(result, text[:dot.Start]...)
+		result = append(result, characters...)
+		result = append(result, text[dot.End:]...)
+		moved = EmptyDot(dot.Add(len(characters)).Start)
+		return
+	}
+}
+
+// MoveLeft moves the dot left one rune. If word is true, it moves the dot to
+// the next word boundary on the left.
+func MoveLeft (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Canon().Constrain(len(text))
+	distance := 0
+	if dot.Empty() {
+		distance = 1
+	}
+	if word {
+		distance = WordToLeft(text, dot.Start)
+	}
+	moved = EmptyDot(dot.Sub(distance).Start)
+	return
+}
+
+// MoveRight moves the dot right one rune. If word is true, it moves the dot to
+// the next word boundary on the right.
+func MoveRight (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Canon().Constrain(len(text))
+	distance := 0
+	if dot.Empty() {
+		distance = 1
+	}
+	if word {
+		distance = WordToRight(text, dot.End)
+	}
+	moved = EmptyDot(dot.Add(distance).End)
+	return
+}
+
+// SelectLeft moves the end of the dot left one rune. If word is true, it moves
+// the end of the dot to the next word boundary on the left.
+func SelectLeft (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Constrain(len(text))
+	distance := 1
+	if word {
+		distance = WordToLeft(text, dot.End)
+	}
+	dot.End -= distance
+	return dot
+}
+
+// SelectRight moves the end of the dot right one rune. If word is true, it
+// moves the end of the dot to the next word boundary on the right.
+func SelectRight (text []rune, dot Dot, word bool) (moved Dot) {
+	dot = dot.Constrain(len(text))
+	distance := 1
+	if word {
+		distance = WordToRight(text, dot.End)
+	}
+	dot.End += distance
+	return dot
+}

theme/theme.go

@@ -0,0 +1,66 @@
+package theme
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/event"
+
+// Role describes the role of an object.
+type Role struct {
+	// Package is an optional namespace field. If specified, it should be
+	// the package name or module name the object is from.
+	Package string
+	
+	// Object specifies what type of object it is. For example:
+	//   - TextInput
+	//   - Table
+	//   - Label
+	//   - Dial
+	// This should correspond directly to the type name of the object.
+	Object string
+}
+
+// R is shorthand for creating a Role structure.
+func R (pack, object string) Role {
+	return Role { Package: pack, Object: object }
+} 
+
+// Color represents a color ID.
+type Color int; const (
+	ColorBackground Color = iota
+	ColorForeground
+	ColorRaised
+	ColorSunken
+	ColorAccent
+)
+
+// RGBA satisfies the color.Color interface.
+func (id Color) RGBA () (r, g, b, a uint32) {
+	if current == nil { return }
+	return current.RGBA(id)
+}
+
+// Theme is an object that can apply a visual style to different objects.
+type Theme interface {
+	// Apply applies the theme to the given object, according to the given
+	// role. This may register event listeners with the given object;
+	// closing the returned cookie will remove them.
+	Apply (tomo.Object, Role) event.Cookie
+	
+	// RGBA returns the RGBA values of the corresponding color ID.
+	RGBA (Color) (r, g, b, a uint32)
+}
+
+var current Theme
+
+// SetTheme sets the theme.
+func SetTheme (theme Theme) {
+	current = theme
+}
+
+// Apply applies the current theme to the given object, according to the given
+// role. This may register event listeners with the given object; closing the
+// returned cookie will remove them.
+func Apply (object tomo.Object, role Role) event.Cookie {
+	if current == nil { return event.NoCookie { } }
+	return current.Apply(object, role)
+}
+

tomo.go

@@ -1,8 +1,10 @@
 package tomo
 
+import "sync"
 import "image"
 import "errors"
 
+var backendLock sync.Mutex
 var backend Backend
 
 // Run initializes a backend, runs the specified callback function, and runs the
@@ -17,7 +19,10 @@ func Run (callback func ()) error {
 
 	back, err := Initialize()
 	if err != nil { return err }
+	
+	backendLock.Lock()
 	backend = back
+	backendLock.Unlock()
 
 	callback()
 	return backend.Run()
@@ -32,29 +37,44 @@ func assertBackend () {
 func Stop () {
 	assertBackend()
 	backend.Stop()
+	
+	backendLock.Lock()
 	backend = nil
+	backendLock.Unlock()
 }
 
+// Do performs a callback function in the event loop thread as soon as possible.
+func Do (callback func ()) {
+	backendLock.Lock()
+	if backend != nil { backend.Do(callback) }
+	backendLock.Unlock()
+}
+
+// NewWindow creates and returns a window within the specified bounds on screen.
 func NewWindow (bounds image.Rectangle) (MainWindow, error) {
 	assertBackend()
 	return backend.NewWindow(bounds)
 }
 
+// NewBox creates and returns a basic Box.
 func NewBox () Box {
 	assertBackend()
 	return backend.NewBox()
 }
 
+// NewTextBox creates and returns a Box that can display text.
 func NewTextBox () TextBox {
 	assertBackend()
 	return backend.NewTextBox()
 }
 
+// NewCanvasBox creates and returns a Box that can display custom graphics.
 func NewCanvasBox () CanvasBox {
 	assertBackend()
 	return backend.NewCanvasBox()
 }
 
+// NewContainerBox creates and returns a Box that can contain other boxes.
 func NewContainerBox () ContainerBox {
 	assertBackend()
 	return backend.NewContainerBox()