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package gui
import (
"fmt"
"image"
)
// Event is something that can happen in an environment.
//
// This package defines only one kind of event: Resize. Other packages implementing environments
// may implement more kinds of events. For example, the win package implements all kinds of
// events for mouse and keyboard.
type Event interface {
String() string
}
// Resize is an event that happens when the environment changes the size of its drawing area.
type Resize struct {
image.Rectangle
}
func (r Resize) String() string {
return fmt.Sprintf("resize/%d/%d/%d/%d", r.Min.X, r.Min.Y, r.Max.X, r.Max.Y)
}
// MakeEventsChan implements a channel of events with an unlimited capacity. It does so
// by creating a goroutine that queues incoming events. Sending to this channel never blocks
// and no events get lost.
//
// The unlimited capacity channel is very suitable for delivering events because the consumer
// may be unavailable for some time (doing a heavy computation), but will get to the events
// later.
//
// An unlimited capacity channel has its dangers in general, but is completely fine for
// the purpose of delivering events. This is because the production of events is fairly
// infrequent and should never out-run their consumption in the long term.
func MakeEventsChan() (<-chan Event, chan<- Event) {
out, in := make(chan Event), make(chan Event)
go func() {
var queue []Event
for {
x, ok := <-in
if !ok {
close(out)
return
}
queue = append(queue, x)
for len(queue) > 0 {
select {
case out <- queue[0]:
queue = queue[1:]
case x, ok := <-in:
if !ok {
for _, x := range queue {
out <- x
}
close(out)
return
}
queue = append(queue, x)
}
}
}
}()
return out, in
}
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