Add class for paint space background

src/com/annimon/turrets/Background.java

@@ -0,0 +1,64 @@
+package com.annimon.turrets;
+
+import java.awt.Color;
+import java.awt.Graphics;
+
+/**
+ *
+ * @author aNNiMON
+ */
+public class Background implements Constants {
+    
+    private static final int STARS_COUNT = (int) Math.sqrt(WIDTH * HEIGHT);
+    
+    private final Color bg, color;
+    private final double shadeAmount;
+
+    public Background() {
+        bg = new Color(Util.randomColor(0, 35));
+        color = new Color(Util.randomColor(150, 235));
+        shadeAmount = Util.rand(0.5, 2.5);
+    }
+    
+    public void draw(Graphics g) {
+        draw(g, WIDTH / 2, HEIGHT / 2, HEIGHT / 3);
+    }
+    
+    public void draw(Graphics g, int planetX, int planetY, int planetRadius) {
+        g.setColor(bg);
+        g.fillRect(0, 0, WIDTH, HEIGHT);
+        drawStars(g, STARS_COUNT);
+        drawPlanet(g, planetX, planetY, planetRadius, color, shadeAmount);
+    }
+    
+    private static void drawStars(Graphics g, int count) {
+        g.setColor(Color.WHITE);
+        for (int i = 0; i < count; i++) {
+            drawPoint(g, Util.rand(WIDTH), Util.rand(HEIGHT));
+        }
+    }
+
+    private static void drawPlanet(Graphics g, int xc, int yc, int rad, Color color, double shade) {
+        g.setColor(Color.BLACK);
+        fillCircle(g, xc, yc, rad, 0, 360);
+        
+        g.setColor(color);
+        for (int y = -rad; y < rad; y++) {
+            int x1 = (int) (Math.sqrt(rad * rad - y * y));
+            for (int x = -x1; x < x1; x++) {
+                final int n = (int) (Util.rand(x1) / shade);
+                if (n > x1 + x) {
+                    drawPoint(g, x + xc, y + yc);
+                }
+            }
+        }
+    }
+
+    private static void fillCircle(Graphics g, int xc, int yc, int radius, int startAngle, int arcAngle) {
+        g.fillArc(xc - radius, yc - radius, 2 * radius, 2 * radius, startAngle, arcAngle);
+    }
+    
+    private static void drawPoint(Graphics g, int x, int y) {
+        g.fillRect(x, y, 1, 1);
+    }
+}