1 files changed, 102 insertions, 0 deletions
diff --git a/layout/layer.go b/layout/layer.go
new file mode 100644
index 0000000..ff6d466
--- /dev/null
+++ b/layout/layer.go
@@ -0,0 +1,102 @@
+package layer
+
+import (
+	"container/list"
+	"errors"
+	"image"
+	"image/draw"
+
+	"github.com/faiface/gui/event"
+)
+
+type ImageFlusher interface {
+	Image() *image.RGBA
+	Flush(r image.Rectangle)
+}
+
+type LayerList struct {
+	event.Dispatch
+	dst    ImageFlusher
+	layers list.List
+}
+
+func (l *LayerList) Dst(dst ImageFlusher) {
+	l.dst = dst
+	for e := l.layers.Back(); e != nil; e = e.Prev() {
+		layer := e.Value.(*Layer)
+		rgba := image.NewRGBA(dst.Image().Bounds())
+		draw.Draw(rgba, layer.rgba.Bounds(), layer.rgba, layer.rgba.Bounds().Min, draw.Src)
+		layer.rgba = rgba
+	}
+}
+
+func (l *LayerList) Push() *Layer {
+	layer := &Layer{
+		lst:  l,
+		rgba: image.NewRGBA(l.dst.Image().Bounds()),
+	}
+	layer.elm = l.layers.PushFront(layer)
+	return layer
+}
+
+func (l *LayerList) Remove(layer *Layer) {
+	if layer.lst == nil {
+		panic(errors.New("layer: Remove: layer already removed"))
+	}
+	l.layers.Remove(layer.elm)
+	layer.lst = nil
+}
+
+func (l *LayerList) Front(layer *Layer) {
+	if layer.lst == nil {
+		panic(errors.New("layer: Front: layer removed"))
+	}
+	l.layers.MoveToFront(layer.elm)
+}
+
+func (l *LayerList) Flush(r image.Rectangle) {
+	if l.dst == nil {
+		panic(errors.New("layer: Flush: no destination"))
+	}
+	draw.Draw(l.dst.Image(), r, image.Transparent, r.Min, draw.Src)
+	for e := l.layers.Back(); e != nil; e = e.Prev() {
+		layer := e.Value.(*Layer)
+		draw.Draw(l.dst.Image(), r, layer.rgba, r.Min, draw.Over)
+	}
+	l.dst.Flush(r)
+}
+
+func (l *LayerList) Happen(event string) bool {
+	if l.Dispatch.Happen(event) {
+		return true
+	}
+	for e := l.layers.Front(); e != nil; e = e.Next() {
+		layer := e.Value.(*Layer)
+		if layer.Happen(event) {
+			return true
+		}
+	}
+	return false
+}
+
+type Layer struct {
+	event.Dispatch
+	lst  *LayerList
+	elm  *list.Element
+	rgba *image.RGBA
+}
+
+func (l *Layer) List() *LayerList {
+	return l.lst
+}
+
+func (l *Layer) Image() *image.RGBA {
+	return l.rgba
+}
+
+func (l *Layer) Flush(r image.Rectangle) {
+	if l.lst == nil {
+		panic(errors.New("layer: Flush: layer removed"))
+	}
+	l.lst.Flush(r)
+}