[orx-view-box] Add demo for proxy programs

orx-view-box/src/commonMain/kotlin/ViewBox.kt

@@ -235,10 +235,12 @@ class ViewBox(
  * @param f [ViewBox] configuration function
  * @return a newly created [ViewBox]
  */
-fun Program.viewBox(area: Rectangle,
+fun Program.viewBox(
+    area: Rectangle,
     translateMouse: Boolean = true,
     translateKeyboard: Boolean = true,
-                    f: ViewBox.() -> Unit): ViewBox {
+    f: ViewBox.() -> Unit = {}
+): ViewBox {
     val viewBox = ViewBox(this, area, translateMouse, translateKeyboard)
     viewBox.f()
     return viewBox

orx-view-box/src/demo/kotlin/DemoProxyProgram01.kt

@@ -0,0 +1,38 @@
+import org.openrndr.Program
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.viewbox.viewBox
+import org.openrndr.math.Vector2
+import kotlin.math.cos
+
+fun Program.program01() {
+    var color: ColorRGBa by this.userProperties
+    color = ColorRGBa.WHITE
+
+    var someFunction : ()->Unit by this.userProperties
+    someFunction = {
+        color = ColorRGBa(Math.random(), Math.random(), Math.random())
+    }
+
+    extend {
+        drawer.fill = color
+        drawer.circle(Vector2(width/2.0, height/2.0), cos(seconds) * 50.0 + 50.0)
+    }
+}
+
+fun main() {
+    application {
+        program {
+            val proxyBox = viewBox(drawer.bounds).apply { program01() }
+            var color: ColorRGBa by proxyBox.userProperties
+            var someFunction: () -> Unit by proxyBox.userProperties
+            color = ColorRGBa.PINK
+            extend {
+                if (Math.random() < 0.01) {
+                    someFunction()
+                }
+                proxyBox.draw()
+            }
+        }
+    }
+}