Add background color support for PNG canvas, fix example code

Author: dwins

geoscript/src/main/scala/render/package.scala

@@ -179,12 +179,17 @@ package render {
 
 package object render {
   type Content = gt.map.MapContent
+  type Color = java.awt.Color
   type Draw = (awt.Graphics2D, Dimension) => Unit
   type Dimension = (Int, Int)
   type Layer = gt.map.Layer
   type StyleLayer = gt.map.Layer
   type DirectLayer = gt.map.DirectLayer
 
+  val White = java.awt.Color.WHITE
+  val Black = java.awt.Color.BLACK
+  val Transparent = new java.awt.Color(0, 0, 0, 0)
+
   private def mkChart(geoms: Traversable[_ <: Geometry]) = {
     import org.geotools.renderer.chart. { GeometryDataset, GeometryRenderer } 
     import org.jfree.chart
@@ -273,7 +278,7 @@ package object render {
   def file(f: String) = new java.io.File(f)
 
   def png[Spec, Out]
-    (dest: Spec = (), size: (Int, Int) = (512, 512))
+    (dest: Spec = (), size: (Int, Int) = (512, 512), background: Color = Transparent)
     (implicit encodable: Encodable[Spec, Out])
     : Canvas[Out]
   = new ImageCanvas(size).map {

geoscript/src/test/scala/tutorial/GeometryAdvanced.scala

@@ -4,30 +4,30 @@ import org.geoscript._, geometry._, render._
 
 object GeometryBuffer extends App {
   val poly = point(0, 0).buffer(1)
-  drawFull(Content(poly), new Window)
+  draw(Content(poly), canvas = new Window)
 }
 
 object GeometrySimplify extends App {
   val poly = point(0, 0).buffer(1)
-  drawFull(Content(simplify(poly, 0.05)), new Window)
-  drawFull(Content(simplify(poly, 0.1)), new Window)
+  draw(Content(simplify(poly, 0.05)), canvas = new Window)
+  draw(Content(simplify(poly, 0.1)), canvas = new Window)
 }
 
 object GeometryTransform extends App {
   val circle = point(0, 0).buffer(1)
-  drawFull(
+  draw(
     Content(Seq(circle, Transform.translated(dx=0.75, dy=0)(circle))),
-    new Window)
+    canvas = new Window)
 
   val box = polygon(Seq((0, 0), (1, 0), (1, 1), (0, 1), (0, 0)))
-  drawFull(
+  draw(
     Content(Seq(
       box, Transform.sheared(x=1, y=0).scaled(x=2, y=2)(box))),
-    new Window)
+      canvas = new Window)
 
   val bar = polygon(Seq((-5,-2),(5,-2),(5,2),(-5,2), (-5,-2)))
   val cross = bar union Transform.rotated(theta=math.toRadians(90))(bar)
-  drawFull(
+  draw(
     Content(Seq(cross, Transform.rotated(theta=math.toRadians(45))(cross))),
-    new Window)
+    canvas = new Window)
 }

geoscript/src/test/scala/tutorial/visualize.scala

@@ -9,5 +9,5 @@ object Visualize extends App {
     Seq(Seq((20,30), (35,35), (30,20), (20,30))))
   val bounds = new ReferencedEnvelope(poly.getEnvelopeInternal, projection.LatLon)
   val window = new Window
-  draw(Content(poly), bounds, window)
+  draw(Content(poly), Stretch(bounds), window)
 }