add window focus event to gui module

1 files changed, 33 insertions, 0 deletions

diff --git a/gui/env.go b/gui/env.go
new file mode 100644
index 0000000..2515417
--- /dev/null
+++ b/gui/env.go
@@ -0,0 +1,33 @@
+package gui
+
+import (
+	"image"
+	"image/draw"
+)
+
+// Env is the most important thing in this package. It is an interactive graphical
+// environment, such as a window.
+//
+// It has two channels: Events() and Draw().
+//
+// The Events() channel produces events, like mouse and keyboard presses, while the
+// Draw() channel receives drawing functions. A drawing function draws onto the
+// supplied draw.Image, which is the drawing area of the Env and returns a rectangle
+// covering the whole part of the image that got changed.
+//
+// An Env guarantees to produce a "resize/<x0>/<y0>/<x1>/<y1>" event as its first event.
+//
+// The Events() channel must be unlimited in capacity. Use MakeEventsChan() to create
+// a channel of events with an unlimited capacity.
+//
+// The Draw() channel may be synchronous.
+//
+// Drawing functions sent to the Draw() channel are not guaranteed to be executed.
+//
+// Closing the Draw() channel results in closing the Env. The Env will subsequently
+// close the Events() channel. On the other hand, when the Events() channel gets closed
+// the user of the Env should subsequently close the Draw() channel.
+type Env interface {
+	Events() <-chan Event
+	Draw() chan<- func(draw.Image) image.Rectangle
+}