Remove AttrIcon

- Has no compelling use case (all use cases need the texture size
  which this attribute cannot provide)
- Duplicates functionality
- The rationale for adding it initially was never that strong

attribute.go

@@ -2,59 +2,37 @@ package tomo
 
 import "image"
 import "image/color"
-import "golang.org/x/image/font"
 import "git.tebibyte.media/tomo/tomo/canvas"
 
-// AttrSet is a set of attributes wherein only one/zero of each attribute type
-// can exist. It is keyed by the AttrNumber of each attribute and must not be
-// modified directly.
-type AttrSet map[int] Attr
-
-// AS builds an AttrSet out of a vararg list of Attr values.
-func AS (attrs ...Attr) AttrSet {
-	set := AttrSet { }
-	set.Add(attrs...)
-	return set
-}
-
-// Add adds attributes to the set.
-func (this AttrSet) Add (attrs ...Attr) {
-	for _, attr := range attrs {
-		this[attr.attr()] = attr
-	}
-}
-
-// MergeUnder takes attributes from another set and adds them if they don't
-// already exist in this one.
-func (this AttrSet) MergeUnder (other AttrSet) {
-	if other == nil { return }
-	for _, attr := range other {
-		if _, exists := this[attr.attr()]; !exists {
-			this.Add(attr)
-		}
-	}
-}
-
-// MergeOver takes attributes from another set and adds them, overriding this
-// one.
-func (this AttrSet) MergeOver (other AttrSet) {
-	if other == nil { return }
-	for _, attr := range other {
-		this.Add(attr)
-	}
-}
-
 // Attr modifies one thing about a box's style.
 type Attr interface {
 	// Equals returns true if both attributes can reasonably be declared
 	// equal.
 	Equals (Attr) bool
-	attr () int
+	Kind   () AttrKind
+	attr   ()
 }
 
+type AttrKind int; const (
+	AttrKindColor AttrKind = iota
+	AttrKindTexture
+	AttrKindTextureMode
+	AttrKindBorder
+	AttrKindMinimumSize
+	AttrKindPadding
+	AttrKindGap
+	AttrKindTextColor
+	AttrKindDotColor
+	AttrKindFace
+	AttrKindWrap
+	AttrKindAlign
+	AttrKindOverflow
+	AttrKindLayout
+)
+
 // AttrColor sets the background color of a box.
 type AttrColor struct { color.Color }
-// AttrTexture sets the texture of a box to a named texture.
+// AttrTexture sets the texture of a box to a texture.
 type AttrTexture struct { canvas.Texture }
 // AttrTextureMode sets the rendering mode of a box's texture.
 type AttrTextureMode TextureMode
@@ -70,8 +48,8 @@ type AttrGap image.Point
 type AttrTextColor struct { color.Color }
 // AttrDotColor sets the text selection color, if the box is a TextBox.
 type AttrDotColor struct { color.Color }
-// AttrFace sets the font face, if the box is a TextBox.
-type AttrFace struct { font.Face }
+// AttrFace sets the type face, if the box is a TextBox.
+type AttrFace Face
 // AttrWrap sets if the text wraps, if the box is a TextBox.
 type AttrWrap bool
 // AttrAlign sets the alignment, if the box is a ContentBox.
@@ -118,8 +96,8 @@ func ADotColor (col color.Color) AttrDotColor {
 	return AttrDotColor { Color: col }
 }
 // AFace is a convenience constructor for the face attribute.
-func AFace (face font.Face) AttrFace {
-	return AttrFace { Face: face }
+func AFace (face Face) AttrFace {
+	return AttrFace(face)
 }
 // AWrap is a convenience constructor for the wrap attribute.
 func AWrap (wrap bool) AttrWrap {
@@ -256,24 +234,32 @@ func (this AttrLayout) Equals (other Attr) bool {
 	return false
 }
 
-// AttrNumber returns the number of an attribute. Each attribute type has a
-// unique number. The exact values of these numbers are not part of the API and
-// may change.
-func AttrNumber (attr Attr) int {
-	return attr.attr()
-}
+func (AttrColor)       Kind () AttrKind { return AttrKindColor }
+func (AttrTexture)     Kind () AttrKind { return AttrKindTexture }
+func (AttrTextureMode) Kind () AttrKind { return AttrKindTextureMode }
+func (AttrBorder)      Kind () AttrKind { return AttrKindBorder }
+func (AttrMinimumSize) Kind () AttrKind { return AttrKindMinimumSize }
+func (AttrPadding)     Kind () AttrKind { return AttrKindPadding }
+func (AttrGap)         Kind () AttrKind { return AttrKindGap }
+func (AttrTextColor)   Kind () AttrKind { return AttrKindTextColor }
+func (AttrDotColor)    Kind () AttrKind { return AttrKindDotColor }
+func (AttrFace)        Kind () AttrKind { return AttrKindFace }
+func (AttrWrap)        Kind () AttrKind { return AttrKindWrap }
+func (AttrAlign)       Kind () AttrKind { return AttrKindAlign }
+func (AttrOverflow)    Kind () AttrKind { return AttrKindOverflow }
+func (AttrLayout)      Kind () AttrKind { return AttrKindLayout }
 
-func (AttrColor)       attr () int { return  0 }
-func (AttrTexture)     attr () int { return  1 }
-func (AttrTextureMode) attr () int { return  2 }
-func (AttrBorder)      attr () int { return  3 }
-func (AttrMinimumSize) attr () int { return  4 }
-func (AttrPadding)     attr () int { return  5 }
-func (AttrGap)         attr () int { return  6 }
-func (AttrTextColor)   attr () int { return  7 }
-func (AttrDotColor)    attr () int { return  8 }
-func (AttrFace)        attr () int { return  9 }
-func (AttrWrap)        attr () int { return 10 }
-func (AttrAlign)       attr () int { return 11 }
-func (AttrOverflow)    attr () int { return 12 }
-func (AttrLayout)      attr () int { return 13 }
+func (AttrColor)       attr () { }
+func (AttrTexture)     attr () { }
+func (AttrTextureMode) attr () { }
+func (AttrBorder)      attr () { }
+func (AttrMinimumSize) attr () { }
+func (AttrPadding)     attr () { }
+func (AttrGap)         attr () { }
+func (AttrTextColor)   attr () { }
+func (AttrDotColor)    attr () { }
+func (AttrFace)        attr () { }
+func (AttrWrap)        attr () { }
+func (AttrAlign)       attr () { }
+func (AttrOverflow)    attr () { }
+func (AttrLayout)      attr () { }

backend.go

@@ -1,8 +1,8 @@
 package tomo
 
-import "sort"
+import "sync"
 import "image"
-import "errors"
+import "git.tebibyte.media/tomo/tomo/data"
 import "git.tebibyte.media/tomo/tomo/canvas"
 
 // Backend is any Tomo implementation. Backends handle window creation, layout,
@@ -33,22 +33,30 @@ type Backend interface {
 	// must reject any canvas that was not made by it.
 	NewCanvas (image.Rectangle) canvas.CanvasCloser
 
-	// SetStyle sets the style that will be used on objects. The backend is
-	// in charge of applying the style to objects. When this method is
-	// called, it must propagate a StyleChange event to all boxes it is
-	// keeping track of.
-	SetStyle (*Style)
+	// ColorRGBA returns the RGBA of a color according to the current style,
+	// as specified in color.Color.RGBA. It may be rendered invalid if the
+	// visual style changes, but the backend must send a StyleChange event
+	// to all managed boxes when this happens.
+	ColorRGBA (id Color) (r, g, b, a uint32)
 
-	// SetIconSet sets the icon set that icons will be pulled from. When
-	// this method is called, it must propagate an IconChange event to all
-	// boxes it is keeping track of.
-	SetIconSet (IconSet)
+	// IconTexture returns the texture of an icon. It may be closed and
+	// therefore rendered invalid if the icon set changes, but the backend
+	// must send an IconSetChange event to all managed boxes when this
+	// happens.
+	IconTexture (Icon, IconSize) canvas.Texture
 
-	// Run runs the event loop until Stop() is called, or the backend
+	// MimeIconTexture returns the texture of an icon corresponding to the
+	// specified MIME type. It may be closed and therefore rendered invalid
+	// if the icon set changes, but the backend must send an IconSetChange
+	// event to all managed boxes when this happens.
+	MimeIconTexture (data.Mime, IconSize) canvas.Texture
+
+	// Run runs the event loop until Stop is called, or the backend
 	// experiences a fatal error.
 	Run () error
 	
-	// Stop must unblock run.
+	// Stop must unblock run. This behavior may only be called from within
+	// tomo.Stop.
 	Stop ()
 
 	// Do performs a callback function in the event loop thread as soon as
@@ -56,54 +64,21 @@ type Backend interface {
 	Do (func ())
 }
 
-// Factory is a function that attempts to instatiate a backend. If the
-// instantiation process fails at any point, it must clean up all resources and
-// return nil and an error explaining what happened.
-type Factory func () (Backend, error)
+var backendLock sync.Mutex
+var backend Backend
 
-var registered []factoryEntry
-type factoryEntry struct {
-	Factory
-	priority int
+func assertBackend () {
+	if backend == nil { panic("nil backend") }
 }
 
-// Register registers a backend factory with the given priority number.
-func Register (priority int, factory Factory) {
-	registered = append(registered, factoryEntry {
-		priority: priority,
-		Factory:  factory,
-	})
-}
+// SetBackend sets the backend that functions in this package will call upon.
+// This function will panic if there is already a backend running.
+func SetBackend (back Backend) {
+	backendLock.Lock()
+	defer backendLock.Unlock()
 
-// initialize instantiates a backend. The first backend (sorted by priority)
-// that does not throw an error when initialized is used. If no backend could be
-// instantiated, this function returns an error. This function should be called
-// only once.
-func initialize () (Backend, error) {
-	backend, err := instantiate()
-	if err != nil { return nil, err }
-	return backend, err
-}
-
-func instantiate () (Backend, error) {
-	if len(registered) < 0 {
-		return nil, errors.New("no available backends")
+	if backend != nil {
+		panic("SetBackend called while another backend was running")
 	}
-
-	// sort backends by priority
-	sort.Slice(registered, func (left, right int) bool {
-		return registered[left].priority < registered[right].priority
-	})
-
-	// attempt to instantiate
-	errorLog := ""
-	for _, factory := range registered {
-		backend, err := factory.Factory()
-		if err == nil {
-			return backend, nil
-		} else {
-			errorLog += "  " + err.Error() + "\n"
-		}
-	}
-	return nil, errors.New("all backends failed:\n" + errorLog)
+	backend = back
 }

go.mod

@@ -1,5 +1,3 @@
 module git.tebibyte.media/tomo/tomo
 
 go 1.20
-
-require golang.org/x/image v0.11.0

go.sum

@@ -1,33 +0,0 @@
-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 v0.11.0 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=
-golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
-golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
-golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
-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 v0.12.0/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=
-golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
-golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

icon.go

@@ -370,46 +370,20 @@ const (
 	IconWeatherStorm                 Icon = "WeatherStorm"
 )
 
-// Texture returns a texture of the corresponding icon ID.
+// Texture returns a texture of the corresponding icon ID. It may be closed and
+// therefore rendered invalid if the icon set changes, so it is necessary to
+// subscribe to the IconSetChange event in order to get a new icon texture when
+// this happens.
 func (id Icon) Texture (size IconSize) canvas.Texture {
-	if iconSet == nil { return nil }
-	return iconSet.Icon(id, size)
-}
-
-// MimeIcon returns an icon corresponding to a MIME type.
-func MimeIcon (mime data.Mime, size IconSize) canvas.Texture {
-	if iconSet == nil { return nil }
-	return iconSet.MimeIcon(mime, size)
-}
-
-// IconSet holds a set of icon textures.
-type IconSet interface {
-	// A word on textures:
-	//
-	// Because textures can be linked to some resource that is outside of
-	// the control of Go's garbage collector, methods of IconSet must not
-	// allocate new copies of a texture each time they are called. It is
-	// fine to lazily load textures and save them for later use, but the
-	// same texture must never be allocated multiple times as this could
-	// cause a memory leak.
-	//
-	// As such, textures returned by these methods must be protected.
-	
-	// Icon returns a texture of the corresponding icon ID. If there is no
-	// suitable option, it should return nil.
-	Icon (Icon, IconSize) canvas.Texture
-
-	// MimeIcon returns a texture of an icon corresponding to a MIME type.
-	// If there is no suitable specific option, it should return a more
-	// generic icon or a plain file icon.
-	MimeIcon (data.Mime, IconSize) canvas.Texture
-}
-
-var iconSet IconSet
-
-// SetIconSet sets the icon set.
-func SetIconSet (set IconSet) {
 	assertBackend()
-	iconSet = set
-	backend.SetIconSet(set)
+	return backend.IconTexture(id, size)
+}
+
+// MimeIconTexture returns an icon corresponding to a MIME type. It may be
+// closed and therefore rendered invalid if the icon set changes, so it is
+// necessary to subscribe to the IconSetChange event in order to get a new icon
+// texture when this happens.
+func MimeIconTexture (mime data.Mime, size IconSize) canvas.Texture {
+	assertBackend()
+	return backend.MimeIconTexture(mime, size)
 }

object.go

@@ -57,8 +57,12 @@ type Box interface {
 	// SetTag adds or removes a named tag.
 	SetTag (string, bool)
 
-	// SetAttr overrides a style attribute.
-	SetAttr(Attr)
+	// SetAttr sets a style attribute, overriding the currently applied
+	// style.
+	SetAttr (Attr)
+	// UnsetAttr reverts a style attribute to whatever is specified by the
+	// currently applied style.
+	UnsetAttr (AttrKind)
 
 	// 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

style.go

@@ -1,80 +0,0 @@
-package tomo
-
-import "fmt"
-import "image/color"
-
-// 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
-}
-
-// String satisfies the fmt.Stringer interface. It follows the format of:
-//   Package.Object
-func (r Role) String () string {
-	return fmt.Sprintf("%s.%s", r.Package, r.Object)
-}
-
-// 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 style == nil { return }
-	return style.Colors[id].RGBA()
-}
-
-var style *Style
-
-// SetStyle sets the style.
-func SetStyle (sty *Style) {
-	assertBackend()
-	style = sty
-	backend.SetStyle(sty)
-}
-
-// Style can apply a visual style to different objects.
-type Style struct {
-	// Rules determines which styles get applied to which Objects.
-	Rules []Rule
-
-	// Colors maps tomo.Color values to color.RGBA values.
-	Colors map[Color] color.Color
-}
-
-// Rule describes under what circumstances should certain style attributes be
-// active.
-type Rule struct {
-	Role Role
-	Tags []string
-	Set  AttrSet
-}
-
-// Ru is shorthand for creating a rule structure
-func Ru (set AttrSet, role Role, tags ...string) Rule {
-	return Rule {
-		Role: role,
-		Tags: tags,
-		Set:  set,
-	}
-}

tomo.go

@@ -1,38 +1,8 @@
 package tomo
 
-import "sync"
 import "image"
-import "errors"
 import "git.tebibyte.media/tomo/tomo/canvas"
 
-var backendLock sync.Mutex
-var backend Backend
-
-// Run initializes a backend, runs the specified callback function, and runs the
-// event loop in that order. This function blocks until Stop is called, or the
-// backend experiences a fatal error.
-func Run (callback func ()) error {
-	if backend != nil {
-		return errors.New("there is already a backend running")
-	}
-
-	back, err := initialize()
-	if err != nil { return err }
-	
-	backendLock.Lock()
-	backend = back
-	backendLock.Unlock()
-
-	callback()
-	// callback may have called tomo.Stop
-	if backend == nil { return nil }
-	return backend.Run()
-}
-
-func assertBackend () {
-	if backend == nil { panic("nil backend") }
-}
-
 // Stop stops the backend, unblocking run. Run may be called again after calling
 // Stop.
 func Stop () {

unit.go

@@ -1,5 +1,6 @@
 package tomo
 
+import "fmt"
 import "image"
 import "image/color"
 
@@ -11,6 +12,16 @@ type Side int; const (
 	SideLeft
 )
 
+func (side Side) String () string {
+	switch side {
+	case SideTop:    return "SideTop"
+	case SideRight:  return "SideRight"
+	case SideBottom: return "SideBottom"
+	case SideLeft:   return "SideLeft"
+	default:         return fmt.Sprintf("Side(%d)", side)
+	}
+}
+
 // Inset represents a rectangle inset that can have a different value for each
 // side.
 type Inset [4]int
@@ -37,6 +48,10 @@ func I (sides ...int) Inset {
 	}
 }
 
+func (inset Inset) String () string {
+	return fmt.Sprintf("%d %d %d %d", inset[0], inset[1], inset[2], inset[3])
+}
+
 // 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
@@ -87,6 +102,12 @@ type Border struct {
 	Color [4]color.Color
 }
 
+func (border Border) String () string {
+	return fmt.Sprintf("%v %v %v %v / %v",
+		border.Color[0], border.Color[1], border.Color[2], border.Color[3],
+		border.Width)
+}
+
 // Align lists basic alignment types.
 type Align int; const (
 	AlignStart Align = iota // similar to left-aligned text
@@ -95,6 +116,16 @@ type Align int; const (
 	AlignEven               // similar to justified text
 )
 
+func (align Align) String () string {
+	switch align {
+	case AlignStart:  return "AlignStart"
+	case AlignMiddle: return "AlignMiddle"
+	case AlignEnd:    return "AlignEnd"
+	case AlignEven:   return "AlignEven"
+	default:          return fmt.Sprintf("Align(%d)", align)
+	}
+}
+
 // TextureMode lists texture rendering modes.
 type TextureMode int; const (
 	TextureModeTile TextureMode = iota
@@ -103,3 +134,92 @@ type TextureMode int; const (
 	// TODO more modes: fit, fill, and stretch
 	// Of course canvas will need to have a concept of this.
 )
+
+func (mode TextureMode) String () string {
+	switch mode {
+	case TextureModeTile:   return "TextureModeTile"
+	case TextureModeCenter: return "TextureModeCenter"
+	default:                return fmt.Sprintf("TextureMode(%d)", mode)
+	}
+}
+
+// Face represents a typeface. 
+type Face struct {
+	// Font specifies the font name. This should be searched for in a list
+	// of installed fonts.
+        Font string
+        // Size is the point size of the face.
+        Size float64
+	// Weight is the weight of the face. If zero, it should be interpreted
+	// as normal (equivalent to 400).
+        Weight int
+        // Italic is how italicized the face is. It ranges from 0 to 1. It is
+        // different from Slant in that it may alter the design of the glyphs
+        // instead of simply skewing them.
+        Italic float64
+        // Slant is how slanted the face is. It ranges from 0 to 1. It is
+        // different from Italic in that it simply skews the glyphs without
+        // altering their design.
+        Slant float64
+}
+
+func (face Face) String () string {
+	return fmt.Sprintf (
+		"%s %fpt W%d I%f S%f",
+		face.Font, face.Size, face.Weight, face.Italic, face.Slant)
+}
+
+// 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
+}
+
+// String satisfies the fmt.Stringer interface. It follows the format of:
+//   Package.Object
+func (r Role) String () string {
+	return fmt.Sprintf("%s.%s", r.Package, r.Object)
+}
+
+// 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
+)
+
+func (id Color) String () string {
+	switch id {
+	case ColorBackground: return "ColorBackground"
+	case ColorForeground: return "ColorForeground"
+	case ColorRaised:     return "ColorRaised"
+	case ColorSunken:     return "ColorSunken"
+	case ColorAccent:     return "ColorAccent"
+	default:              return fmt.Sprintf("Color(%d)", id)
+	}
+}
+
+// RGBA satisfies the color.Color interface. The result of this method may be
+// rendered invalid if the visual style changes, so it is often necessary to
+// subscribe to the StyleChange event in order to get new RGBA values when this
+// happens.
+func (id Color) RGBA () (r, g, b, a uint32) {
+	assertBackend()
+	return backend.ColorRGBA(id)
+}