1 files changed, 102 insertions, 0 deletions
diff --git a/env.go b/env.go
index 05276b5..f5f31cf 100644
--- a/env.go
+++ b/env.go
@@ -28,3 +28,105 @@ type Env interface {
 
 	killer
 }
+
+type env struct {
+	events     <-chan Event
+	draw       chan<- func(draw.Image) image.Rectangle
+	attachChan chan<- attachable
+	kill       chan<- bool
+	dead       <-chan bool
+	detachChan <-chan bool
+}
+
+// newEnv makes an Env that receives Events from, and sends draw functions to, the parent.
+//
+// Each Event received from parent is passed to filterEvents() along with the Events() channel
+// of the Env. Each draw function received from the Env's Draw() channel is passed to
+// filterDraws() along with the Draw() channel of the parent Env.
+//
+// filterEvents() and filterDraws() can be used to, e.g., simply forward the Event or draw function
+// to the channel, modify it before sending, not send it at all, or produce some other side-effects.
+//
+// shutdown() is called before the Env dies.
+func newEnv(parent Env,
+	filterEvents func(Event, chan<- Event),
+	filterDraws func(func(draw.Image) image.Rectangle, chan<- func(draw.Image) image.Rectangle),
+	shutdown func(),
+) Env {
+	eventsOut, eventsIn := makeEventsChan()
+	drawChan := make(chan func(draw.Image) image.Rectangle)
+	child := newAttachHandler()
+	kill := make(chan bool)
+	dead := make(chan bool)
+	detachFromParent := make(chan bool)
+
+	go func() {
+		defer func() {
+			dead <- true
+			close(dead)
+		}()
+		defer func() {
+			detachFromParent <- true
+			close(detachFromParent)
+		}()
+		defer shutdown()
+		defer close(eventsIn)
+		defer close(drawChan)
+		defer close(kill)
+		defer func() {
+			go drain(drawChan)
+			child.kill <- true
+			<-child.dead
+		}()
+
+		for {
+			select {
+			case e := <-parent.Events():
+				filterEvents(e, eventsIn)
+			case d := <-drawChan:
+				filterDraws(d, parent.Draw())
+			case <-kill:
+				return
+			}
+		}
+	}()
+
+	e := env{
+		events:     eventsOut,
+		draw:       drawChan,
+		attachChan: child.attach(),
+		kill:       kill,
+		dead:       dead,
+		detachChan: detachFromParent,
+	}
+	parent.attach() <- e
+	return e
+}
+
+func (e env) Events() <-chan Event {
+	return e.events
+}
+
+func (e env) Draw() chan<- func(draw.Image) image.Rectangle {
+	return e.draw
+}
+
+func (e env) Kill() chan<- bool {
+	return e.kill
+}
+
+func (e env) Dead() <-chan bool {
+	return e.dead
+}
+
+func (e env) attach() chan<- attachable {
+	return e.attachChan
+}
+
+func (e env) detach() <-chan bool {
+	return e.detachChan
+}
+
+func send[T any](v T, c chan<- T) {
+	c <- v
+}