From 7ca2e125c17bd541340bce55623bd40cf88ce64f Mon Sep 17 00:00:00 2001
From: Li Haoyi <haoyi@dropbox.com>
Date: Thu, 20 Nov 2014 02:07:02 -0800
Subject: Scala-async chapter works

---
 examples/demos/src/main/scala/advanced/Async.scala | 120 +++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 examples/demos/src/main/scala/advanced/Async.scala

(limited to 'examples/demos/src/main/scala/advanced/Async.scala')

diff --git a/examples/demos/src/main/scala/advanced/Async.scala b/examples/demos/src/main/scala/advanced/Async.scala
new file mode 100644
index 0000000..481e80e
--- /dev/null
+++ b/examples/demos/src/main/scala/advanced/Async.scala
@@ -0,0 +1,120 @@
+package advanced
+
+import org.scalajs.dom
+import concurrent._
+import async.Async._
+import scala.scalajs.js.annotation.JSExport
+import scalajs.concurrent.JSExecutionContext.Implicits.queue
+
+@JSExport
+object Async {
+  def init(canvas: dom.HTMLCanvasElement) = {
+    val renderer = canvas.getContext("2d")
+      .asInstanceOf[dom.CanvasRenderingContext2D]
+
+    canvas.style.backgroundColor = "#f8f8f8"
+    canvas.height = canvas.parentElement.clientHeight
+    canvas.width = canvas.parentElement.clientWidth
+
+    renderer.lineWidth = 5
+    renderer.strokeStyle = "red"
+    renderer.fillStyle = "cyan"
+    renderer
+  }
+  @JSExport
+  def main(canvas: dom.HTMLCanvasElement) = {
+    val renderer = init(canvas)
+    // async
+    def rect = canvas.getBoundingClientRect()
+
+    type ME = dom.MouseEvent
+    val mousemove =
+      Channel[ME](canvas.onmousemove = _)
+    val mouseup =
+      Channel[ME](canvas.onmouseup = _)
+    val mousedown =
+      Channel[ME](canvas.onmousedown = _)
+
+    async{
+      while(true){
+        val start = await(mousedown())
+        renderer.beginPath()
+        renderer.moveTo(
+          start.clientX - rect.left,
+          start.clientY - rect.top
+        )
+
+        var res = await(mousemove | mouseup)
+        while(res.`type` == "mousemove"){
+          renderer.lineTo(
+            res.clientX - rect.left,
+            res.clientY - rect.top
+          )
+          renderer.stroke()
+          res = await(mousemove | mouseup)
+        }
+
+        renderer.fill()
+        await(mouseup())
+        renderer.clearRect(0, 0, 1000, 1000)
+      }
+    }
+  }
+  @JSExport
+  def main0(canvas: dom.HTMLCanvasElement) = {
+    val renderer = init(canvas)
+    // traditional
+    def rect = canvas.getBoundingClientRect()
+
+    var dragState = 0
+
+    canvas.onmousemove ={(e: dom.MouseEvent) =>
+      if (dragState == 1) {
+        renderer.lineTo(
+          e.clientX - rect.left,
+          e.clientY - rect.top
+        )
+        renderer.stroke()
+      }
+    }
+    canvas.onmouseup = {(e: dom.MouseEvent) =>
+      if(dragState == 1) {
+        renderer.fill()
+        dragState = 2
+      }else if (dragState == 2){
+        renderer.clearRect(0, 0, 1000, 1000)
+        dragState = 0
+      }
+    }
+    canvas.onmousedown ={(e: dom.MouseEvent) =>
+      if (dragState == 0) {
+        dragState = 1
+        renderer.beginPath()
+        renderer.moveTo(
+          e.clientX - rect.left,
+          e.clientY - rect.top
+        )
+      }
+    }
+  }
+}
+
+case class Channel[T](init: (T => Unit) => Unit){
+  init(update)
+  private[this] var value: Promise[T] = null
+  def apply(): Future[T] = {
+    value = Promise[T]()
+    value.future
+  }
+  def update(t: T): Unit = {
+    if (value != null && !value.isCompleted) value.success(t)
+  }
+  def |(other: Channel[T]): Future[T] = {
+    val p = Promise[T]()
+    for{
+      f <- Seq(other(), this())
+      t <- f
+    } p.trySuccess(t)
+    p.future
+  }
+}
\ No newline at end of file
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