It displays things on a screen

box.go

@@ -237,9 +237,11 @@ func (this *box) recursiveRedo () {
 }
 
 func (this *box) invalidateDraw () {
+	if this.parent == nil { return }
 	this.parent.window().invalidateDraw(this)
 }
 
 func (this *box) invalidateLayout () {
+	if this.parent == nil { return }
 	this.parent.window().invalidateLayout(this)
 }

canvas/canvas.go

@@ -14,18 +14,19 @@ type Canvas struct {
 }
 
 // New creates a new canvas from a bounding rectangle.
-func New (x *xgbutil.XUtil, bounds image.Rectangle) Canvas {
+func New (x *xgbutil.XUtil, bounds image.Rectangle) *Canvas {
-	return Canvas { xgraphics.New(x, bounds) }
+	return NewFrom(xgraphics.New(x, bounds))
 }
 
 // NewFrom creates a new canvas from an existing xgraphics.Image.
-func NewFrom (image *xgraphics.Image) Canvas {
+func NewFrom (image *xgraphics.Image) *Canvas {
-	return Canvas { image }
+	if image == nil { return nil }
+	return &Canvas { image }
 }
 
 // Pen returns a new drawing context.
-func (this Canvas) Pen () canvas.Pen {
+func (this *Canvas) Pen () canvas.Pen {
-	return pen {
+	return &pen {
 		image: this.Image,
 		gfx:   ggfx.Image[uint8] {
 			Pix:    this.Image.Pix,
@@ -37,16 +38,25 @@ func (this Canvas) Pen () canvas.Pen {
 }
 
 // Clip returns a sub-canvas of this canvas.
-func (this Canvas) Clip (bounds image.Rectangle) canvas.Canvas {
+func (this *Canvas) Clip (bounds image.Rectangle) canvas.Canvas {
-	return Canvas { this.Image.SubImage(bounds).(*xgraphics.Image) }
+	this.assert()
+	subImage := this.Image.SubImage(bounds)
+	if subImage == nil { return nil }
+	xImage := subImage.(*xgraphics.Image)
+	return &Canvas { xImage }
 }
 
 // Push pushes this canvas to the screen.
-func (this Canvas) Push (window xproto.Window) {
+func (this *Canvas) Push (window xproto.Window) {
+	this.assert()
 	this.XDraw()
 	this.XExpPaint(window, this.Bounds().Min.X, this.Bounds().Min.Y)
 }
 
+func (this *Canvas) assert () {
+	if this == nil { panic("nil canvas") }
+}
+
 // TODO: we need to implement:
 //  - cap
 //  - joint
@@ -65,7 +75,7 @@ type pen struct {
 	fill   [4]uint8
 }
 
-func (this pen) Rectangle (bounds image.Rectangle) {
+func (this *pen) Rectangle (bounds image.Rectangle) {
 	if this.weight == 0 {
 		this.gfx.FillRectangle(this.fill[:], bounds)
 	} else {
@@ -73,7 +83,7 @@ func (this pen) Rectangle (bounds image.Rectangle) {
 	}
 }
 
-func (this pen) Path (points ...image.Point) {
+func (this *pen) Path (points ...image.Point) {
 	if this.weight == 0 {
 		this.gfx.FillPolygon(this.fill[:], points...)
 	} else if this.closed {
@@ -83,21 +93,21 @@ func (this pen) Path (points ...image.Point) {
 	}
 }
  
-func (this pen) Closed       (closed bool)              { this.closed = closed }
+func (this *pen) Closed       (closed bool)              { this.closed = closed }
-func (this pen) Cap          (endCap canvas.Cap)        { this.endCap = endCap }
+func (this *pen) Cap          (endCap canvas.Cap)        { this.endCap = endCap }
-func (this pen) Joint        (joint  canvas.Joint)      { this.joint  = joint  }
+func (this *pen) Joint        (joint  canvas.Joint)      { this.joint  = joint  }
-func (this pen) StrokeWeight (weight int)               { this.weight = weight }
+func (this *pen) StrokeWeight (weight int)               { this.weight = weight }
-func (this pen) StrokeAlign  (align canvas.StrokeAlign) { this.align  = align  }
+func (this *pen) StrokeAlign  (align canvas.StrokeAlign) { this.align  = align  }
 
-func (this pen) Stroke (stroke color.Color) { this.stroke = convertColor(stroke) }
+func (this *pen) Stroke (stroke color.Color) { this.stroke = convertColor(stroke) }
-func (this pen) Fill (fill color.Color)     { this.fill   = convertColor(fill)   }
+func (this *pen) Fill (fill color.Color)     { this.fill   = convertColor(fill)   }
 
 func convertColor (c color.Color) [4]uint8 {
 	r, g, b, a := c.RGBA()
 	return [4]uint8 {
 		uint8(b >> 8),
 		uint8(g >> 8),
-		uint8(a >> 8),
 		uint8(r >> 8),
+		uint8(a >> 8),
 	}
 }

event.go

@@ -10,8 +10,11 @@ func (window *window) handleExpose (
 	connection *xgbutil.XUtil,
 	event xevent.ExposeEvent,
 ) {
+	if window.xCanvas == nil {
+		window.reallocateCanvas()
+	}
 	window.compressExpose(*event.ExposeEvent)
-	window.xCanvas.Push(window.xWindow.Id)
+	window.pushAll()
 }
 
 func (window *window) updateBounds () {
@@ -33,7 +36,7 @@ func (window *window) handleConfigureNotify (
 	event xevent.ConfigureNotifyEvent,
 ) {
 	if window.root == nil { return }
-
+	
 	configureEvent := *event.ConfigureNotifyEvent
 	
 	newWidth  := int(configureEvent.Width)
@@ -46,7 +49,7 @@ func (window *window) handleConfigureNotify (
 	if sizeChanged {
 		configureEvent = window.compressConfigureNotify(configureEvent)
 		window.reallocateCanvas()
-		window.root.SetBounds(window.metrics.bounds)
+
 		// TODO figure out what to do with this
 		// if !window.exposeEventFollows(configureEvent) {
 		// }

system.go

@@ -2,7 +2,6 @@ package x
 
 import "image"
 import "git.tebibyte.media/tomo/tomo"
-import "git.tebibyte.media/tomo/x/canvas"
 import "git.tebibyte.media/tomo/tomo/canvas"
 
 type boxSet map[anyBox] struct { }
@@ -46,11 +45,17 @@ type anyBox interface {
 }
 
 func (window *window) SetRoot (root tomo.Object) {
-	box := root.Box().(anyBox)
+	if window.root != nil {
-	window.root.setParent(nil)
+		window.root.setParent(nil)
-	box.setParent(window)
+	}
-	window.invalidateLayout(box)
+	if root == nil {
-	window.root = box
+		window.root = nil
+	} else {
+		box := root.Box().(anyBox)
+		box.setParent(window)
+		window.invalidateLayout(box)
+		window.root = box
+	}
 }
 
 func (window *window) window () *window {
@@ -78,11 +83,20 @@ func (window *window) focus (box anyBox) {
 }
 
 func (window *window) afterEvent () {
+	if window.xCanvas == nil { return }
+
 	if window.needRedo {
+		// set child bounds
+		childBounds := window.metrics.bounds
+		childBounds = childBounds.Sub(childBounds.Min)
+		window.root.SetBounds(childBounds)
+
+		// full relayout/redraw		
 		if window.root != nil {
 			window.root.recursiveRedo()
 		}
-		window.xCanvas.Push(window.xWindow.Id)
+		window.pushAll()
+		window.needRedo = false
 		return
 	}
 
@@ -95,5 +109,7 @@ func (window *window) afterEvent () {
 		box.doDraw()
 		toPush = toPush.Union(box.Bounds())
 	}
-	window.xCanvas.Clip(toPush).(xcanvas.Canvas).Push(window.xWindow.Id)
+	if !toPush.Empty() {
+		window.pushRegion(toPush)
+	}
 }

window.go

@@ -24,7 +24,7 @@ type window struct {
 	backend *Backend
 	xWindow *xwindow.Window
 	xImage  *xgraphics.Image
-	xCanvas xcanvas.Canvas
+	xCanvas *xcanvas.Canvas
 
 	title string
 
@@ -55,7 +55,7 @@ func (backend *Backend) NewWindow (
 	output tomo.MainWindow,
 	err error,
 ) {
-	if backend == nil { panic("nil backend") }
+	backend.assert()
 	window, err := backend.newWindow(bounds, false)
 	
 	output = mainWindow { window: window }
@@ -104,10 +104,10 @@ func (backend *Backend) newWindow (
 		window.Close()
 	})
 
-	// xevent.ExposeFun(window.handleExpose).
+	xevent.ExposeFun(window.handleExpose).
-		// Connect(backend.x, window.xWindow.Id)
+		Connect(backend.x, window.xWindow.Id)
-	// xevent.ConfigureNotifyFun(window.handleConfigureNotify).
+	xevent.ConfigureNotifyFun(window.handleConfigureNotify).
-		// Connect(backend.x, window.xWindow.Id)
+		Connect(backend.x, window.xWindow.Id)
 	// xevent.KeyPressFun(window.handleKeyPress).
 		// Connect(backend.x, window.xWindow.Id)
 	// xevent.KeyReleaseFun(window.handleKeyRelease).
@@ -130,8 +130,6 @@ func (backend *Backend) newWindow (
 	window.metrics.bounds = bounds
 	window.setMinimumSize(8, 8)
 
-	window.reallocateCanvas()
-
 	backend.windows[window.xWindow.Id] = window
 
 	output = window
@@ -243,14 +241,6 @@ func (window *window) Paste (callback func (data.Data, error), accept ...data.Mi
 }
 
 func (window *window) Show () {
-	// fill the screen with black if there is no active child
-	if window.root == nil {
-		window.xCanvas.For (func (x, y int) xgraphics.BGRA {
-			return xgraphics.BGRA { }
-		})
-		window.xCanvas.Push(window.xWindow.Id)
-	}
-
 	window.xWindow.Map()
 	if window.shy { window.grabInput() }
 }
@@ -314,8 +304,11 @@ func (window *window) setClientLeader (leader *window) error {
 }
 
 func (window *window) reallocateCanvas () {
-	previousWidth  := window.xCanvas.Bounds().Dx()
+	var previousWidth, previousHeight int
-	previousHeight := window.xCanvas.Bounds().Dy()
+	if window.xCanvas != nil {
+		previousWidth  = window.xCanvas.Bounds().Dx()
+		previousHeight = window.xCanvas.Bounds().Dy()
+	}
 	
 	newWidth  := window.metrics.bounds.Dx()
 	newHeight := window.metrics.bounds.Dy()
@@ -325,7 +318,7 @@ func (window *window) reallocateCanvas () {
 	allocStep := 128
 	
 	if larger || smaller {
-		if window.xCanvas.Image != nil {
+		if window.xCanvas != nil {
 			window.xCanvas.Destroy()
 		}
 		window.xCanvas = xcanvas.NewFrom(xgraphics.New (
@@ -336,9 +329,28 @@ func (window *window) reallocateCanvas () {
 				(newHeight / allocStep + 1) * allocStep)))
 		window.xCanvas.CreatePixmap()
 	}
+
 	window.needRedo = true
 }
 
+func (window *window) pushAll () {
+	if window.xCanvas != nil {
+		window.xCanvas.Push(window.xWindow.Id)
+	}
+}
+
+func (window *window) pushRegion (region image.Rectangle) {
+	if window.xCanvas == nil {
+		return
+	}
+	
+	subCanvas := window.xCanvas.Clip(region)
+	if subCanvas == nil {
+		return
+	}
+	subCanvas.(*xcanvas.Canvas).Push(window.xWindow.Id)
+}
+
 func (window *window) setMinimumSize (width, height int) {
 	if width  < 8 { width  = 8 }
 	if height < 8 { height = 8 }