added missing file;

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/System/gui.scala	Thu Apr 04 18:25:47 2013 +0200
@@ -0,0 +1,121 @@
+/*  Title:      Pure/System/gui.scala
+    Author:     Makarius
+
+Elementary GUI tools.
+*/
+
+package isabelle
+
+
+import java.awt.{Image, Component, Toolkit}
+import javax.swing.{ImageIcon, JOptionPane, UIManager}
+
+import scala.swing.{ComboBox, TextArea, ScrollPane}
+import scala.swing.event.SelectionChanged
+
+
+object GUI
+{
+  /* Swing look-and-feel */
+
+  def get_laf(): String =
+  {
+    def laf(name: String): Option[String] =
+      UIManager.getInstalledLookAndFeels().find(_.getName == name).map(_.getClassName)
+
+    if (Platform.is_windows || Platform.is_macos)
+      UIManager.getSystemLookAndFeelClassName()
+    else
+      laf("Nimbus") orElse laf("GTK+") getOrElse
+        UIManager.getCrossPlatformLookAndFeelClassName()
+  }
+
+  def init_laf(): Unit = UIManager.setLookAndFeel(get_laf())
+
+
+  /* simple dialogs */
+
+  def scrollable_text(txt: String, width: Int = 60, editable: Boolean = false): ScrollPane =
+  {
+    val text = new TextArea(txt)
+    if (width > 0) text.columns = width
+    text.editable = editable
+    new ScrollPane(text)
+  }
+
+  private def simple_dialog(kind: Int, default_title: String,
+    parent: Component, title: String, message: Seq[Any])
+  {
+    Swing_Thread.now {
+      val java_message = message map { case x: scala.swing.Component => x.peer case x => x }
+      JOptionPane.showMessageDialog(parent,
+        java_message.toArray.asInstanceOf[Array[AnyRef]],
+        if (title == null) default_title else title, kind)
+    }
+  }
+
+  def dialog(parent: Component, title: String, message: Any*) =
+    simple_dialog(JOptionPane.PLAIN_MESSAGE, null, parent, title, message)
+
+  def warning_dialog(parent: Component, title: String, message: Any*) =
+    simple_dialog(JOptionPane.WARNING_MESSAGE, "Warning", parent, title, message)
+
+  def error_dialog(parent: Component, title: String, message: Any*) =
+    simple_dialog(JOptionPane.ERROR_MESSAGE, "Error", parent, title, message)
+
+  def confirm_dialog(parent: Component, title: String, option_type: Int, message: Any*): Int =
+    Swing_Thread.now {
+      val java_message = message map { case x: scala.swing.Component => x.peer case x => x }
+      JOptionPane.showConfirmDialog(parent,
+        java_message.toArray.asInstanceOf[Array[AnyRef]], title,
+          option_type, JOptionPane.QUESTION_MESSAGE)
+    }
+
+
+  /* zoom box */
+
+  class Zoom_Box(apply_factor: Int => Unit) extends ComboBox[String](
+    List("50%", "70%", "85%", "100%", "125%", "150%", "175%", "200%", "300%", "400%"))
+  {
+    val Factor = "([0-9]+)%?".r
+    def parse(text: String): Int =
+      text match {
+        case Factor(s) =>
+          val i = Integer.parseInt(s)
+          if (10 <= i && i <= 1000) i else 100
+        case _ => 100
+      }
+
+    def print(i: Int): String = i.toString + "%"
+
+    def set_item(i: Int) {
+      peer.getEditor match {
+        case null =>
+        case editor => editor.setItem(print(i))
+      }
+    }
+
+    makeEditable()(c => new ComboBox.BuiltInEditor(c)(text => print(parse(text)), x => x))
+    reactions += {
+      case SelectionChanged(_) => apply_factor(parse(selection.item))
+    }
+    listenTo(selection)
+    selection.index = 3
+    prototypeDisplayValue = Some("00000%")
+  }
+
+
+  /* screen resolution */
+
+  def resolution_scale(): Double = Toolkit.getDefaultToolkit.getScreenResolution.toDouble / 72
+  def resolution_scale(i: Int): Int = (i.toDouble * resolution_scale()).round.toInt
+
+
+  /* icon */
+
+  def isabelle_icon(): ImageIcon =
+    new ImageIcon(Isabelle_System.platform_path(Path.explode("~~/lib/logo/isabelle.gif")))
+
+  def isabelle_image(): Image = isabelle_icon().getImage
+}
+