add layers

1 files changed, 67 insertions, 0 deletions

diff --git a/layers/layers.go b/layers/layers.go
new file mode 100644
index 0000000..6c1b560
--- /dev/null
+++ b/layers/layers.go
@@ -0,0 +1,67 @@
+package layers
+
+import (
+	"container/list"
+	"errors"
+	"image"
+	"image/draw"
+)
+
+type Layers struct {
+	dst    draw.Image
+	r      image.Rectangle
+	layers list.List
+}
+
+func (l *Layers) Dst(dst draw.Image, r image.Rectangle) {
+	l.dst = dst
+	l.r = r
+	for e := l.layers.Front(); e != nil; e = e.Next() {
+		layer := e.Value.(*Layer)
+		rgba := image.NewRGBA(r)
+		draw.Draw(rgba, layer.rgba.Bounds(), layer.rgba, layer.rgba.Bounds().Min, draw.Src)
+		layer.rgba = rgba
+	}
+}
+
+func (l *Layers) Push() *Layer {
+	layer := &Layer{
+		l:    l,
+		rgba: image.NewRGBA(l.r),
+	}
+	layer.e = l.layers.PushBack(layer)
+	return layer
+}
+
+func (l *Layers) Flush(r image.Rectangle) {
+	if l.dst == nil {
+		panic(errors.New("layers: Flush: no destination"))
+	}
+	draw.Draw(l.dst, r, image.Transparent, r.Min, draw.Src)
+	for e := l.layers.Front(); e != nil; e = e.Next() {
+		layer := e.Value.(*Layer)
+		draw.Draw(l.dst, r, layer.rgba, r.Min, draw.Over)
+	}
+}
+
+type Layer struct {
+	l    *Layers
+	e    *list.Element
+	rgba *image.RGBA
+}
+
+func (l *Layer) Remove() {
+	l.l.layers.Remove(l.e)
+}
+
+func (l *Layer) Front() {
+	l.l.layers.MoveToFront(l.e)
+}
+
+func (l *Layer) Image() *image.RGBA {
+	return l.rgba
+}
+
+func (l *Layer) Flush(r image.Rectangle) {
+	l.l.Flush(r)
+}