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package gui
import (
"image"
"image/draw"
)
// Mux can be used to multiplex an Env, let's call it a root Env. Mux implements a way to
// create multiple virtual Envs that all interact with the root Env. They receive the same
// events and their draw functions get redirected to the root Env.
type Mux struct {
addEventsIn chan<- chan<- Event
size sharedVal[image.Rectangle]
draw chan<- func(draw.Image) image.Rectangle
}
// NewMux creates a new Mux that multiplexes the given Env. It returns the Mux along with
// a master Env. The master Env is just like any other Env created by the Mux, except that
// closing the Draw() channel on the master Env closes the whole Mux and all other Envs
// created by the Mux.
func NewMux(env Env) (mux *Mux, master Env) {
addEventsIn := make(chan chan<- Event)
size := newSharedVal[image.Rectangle]()
drawChan := make(chan func(draw.Image) image.Rectangle)
mux = &Mux{
addEventsIn: addEventsIn,
size: size,
draw: drawChan,
}
go func() {
var eventsIns []chan<- Event
defer close(env.Draw())
defer close(addEventsIn)
defer size.close()
defer func() {
for _, eventsIn := range eventsIns {
close(eventsIn)
}
}()
for {
select {
case d, ok := <-drawChan:
if !ok { // closed by master env
return
}
env.Draw() <- d
case e, ok := <-env.Events():
if !ok {
return
}
if resize, ok := e.(Resize); ok {
size.set <- resize.Rectangle
}
for _, eventsIn := range eventsIns {
eventsIn <- e
}
case eventsIn := <-addEventsIn:
eventsIns = append(eventsIns, eventsIn)
}
}
}()
master = mux.makeEnv(true)
return mux, master
}
// MakeEnv creates a new virtual Env that interacts with the root Env of the Mux. Closing
// the Draw() channel of the Env will not close the Mux, or any other Env created by the Mux
// but will delete the Env from the Mux.
func (mux *Mux) MakeEnv() Env {
return mux.makeEnv(false)
}
type muxEnv struct {
events <-chan Event
draw chan<- func(draw.Image) image.Rectangle
}
func (m *muxEnv) Events() <-chan Event { return m.events }
func (m *muxEnv) Draw() chan<- func(draw.Image) image.Rectangle { return m.draw }
func (mux *Mux) makeEnv(master bool) Env {
eventsOut, eventsIn := MakeEventsChan()
drawChan := make(chan func(draw.Image) image.Rectangle)
env := &muxEnv{eventsOut, drawChan}
mux.addEventsIn <- eventsIn
// make sure to always send a resize event to a new Env
eventsIn <- Resize{mux.size.get()}
go func() {
func() {
// When the master Env gets its Draw() channel closed, it closes all the Events()
// channels of all the children Envs, and it also closes the internal draw channel
// of the Mux. Otherwise, closing the Draw() channel of the master Env wouldn't
// close the Env the Mux is muxing. However, some child Envs of the Mux may still
// send some drawing commmands before they realize that their Events() channel got
// closed.
//
// That is perfectly fine if their drawing commands simply get ignored. This down here
// is a little hacky, but (I hope) perfectly fine solution to the problem.
//
// When the internal draw channel of the Mux gets closed, the line marked with ! will
// cause panic. We recover this panic, then we receive, but ignore all furhter draw
// commands, correctly draining the Env until it closes itself.
defer func() {
if recover() != nil {
drain(drawChan)
}
}()
for d := range drawChan {
mux.draw <- d // !
}
}()
if master {
close(mux.draw)
}
}()
return env
}
func drain[T any](c <-chan T) { for range c {} }
|