Migrate Starfield example to Graphics Example

This change migrates the Starfield animation effect from the
SWT-OldSchoolEffect repository to the standard SWT Graphics Example.

- Created StarfieldTab.java by extending AnimatedGraphicsTab.
- Registered StarfieldTab in GraphicsExample.java.
- Added localized strings to examples_graphics.properties.

Author: vogella

examples/org.eclipse.swt.examples/src/examples_graphics.properties

@@ -83,6 +83,7 @@ Rectangle=Rectangle
 Oval=Oval
 Word=Word
 Star=Star
+Starfield=Starfield
 Triangles=Triangles
 Default=Default
 RegionClipping=Region Clipping
@@ -184,5 +185,6 @@ rgbDescription=Miscellaneous tab that demonstrates emerging colors from layering
 RegionClippingDescription=This tab demonstrates how to apply a region clipping and the effects of applying one.  It also demonstrates the operations that can be applied between two regions.
 ShapesDescription=This tab draws 3D shapes (in 2D) using various line styles.
 SpiralDescription=Miscellaneous tab that presents a spiral consisting of the number of petals specified.
+StarfieldDescription=This is a miscellaneous demonstration that uses the drawPoint() operation to simulate a moving starfield.
 StarPolygonDescription=This tab draws a polygon and shows the effects of setting different fill rules: SWT.FILL_WINDING or SWT.FILL_EVEN_ODD
 AntialiasingTextDesc=This tab demonstrates antialiasing for text. Antialiasing is used for smoothing jagged edges in graphics. This tab allows the user to see the effects of different antialiasing values.

examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/graphics/GraphicsExample.java

@@ -469,6 +469,7 @@ GraphicsTab[] createTabs() {
 		new LineStyleTab(this),
 		new LineJoinTab(this),
 		new RegionClippingTab(this),
+		new StarfieldTab(this),
 		new CustomAlphaTab(this),
 		new TextAntialiasTab(this),
 		new GraphicAntialiasTab(this),

examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/graphics/StarfieldTab.java

@@ -0,0 +1,123 @@
+/*******************************************************************************
+ * Copyright (c) 2018 Laurent Caron and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Laurent Caron (laurent.caron at gmail dot com) - Original Version
+ *     IBM Corporation - adaptation to GraphicsExample
+ *******************************************************************************/
+
+package org.eclipse.swt.examples.graphics;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.graphics.Color;
+import org.eclipse.swt.graphics.GC;
+
+/**
+ * This tab displays a starfield animation.
+ */
+public class StarfieldTab extends AnimatedGraphicsTab {
+
+	private static final int NUMBER_OF_STARS = 1020;
+	private Star[] stars;
+
+	static class Star {
+		float xpos, ypos;
+		int zpos, speed;
+		int color;
+	}
+
+	public StarfieldTab(GraphicsExample example) {
+		super(example);
+	}
+
+	@Override
+	public String getCategory() {
+		return GraphicsExample.getResourceString("Misc"); //$NON-NLS-1$
+	}
+
+	@Override
+	public String getText() {
+		return GraphicsExample.getResourceString("Starfield"); //$NON-NLS-1$
+	}
+
+	@Override
+	public String getDescription() {
+		return GraphicsExample.getResourceString("StarfieldDescription"); //$NON-NLS-1$
+	}
+
+	@Override
+	public int getInitialAnimationTime() {
+		return 10;
+	}
+
+	@Override
+	public void next(int width, int height) {
+		if (stars == null) return;
+
+		for (int i = 0; i < NUMBER_OF_STARS; i++) {
+			stars[i].zpos -= stars[i].speed;
+
+			if (stars[i].zpos <= 0) {
+				stars[i] = initStar(i + 1);
+			}
+
+			/* compute 3D position */
+			final int tempx = (int) (stars[i].xpos / stars[i].zpos + width / 2);
+			final int tempy = (int) (stars[i].ypos / stars[i].zpos + height / 2);
+
+			if (tempx < 0 || tempx > width - 1 || tempy < 0 || tempy > height - 1) /* check if a star leaves the screen */
+			{
+				stars[i] = initStar(i + 1);
+			}
+		}
+	}
+
+	@Override
+	public void paint(GC gc, int width, int height) {
+		if (stars == null) {
+			stars = new Star[NUMBER_OF_STARS];
+			for (int i = 0; i < NUMBER_OF_STARS; i++) {
+				stars[i] = initStar(i + 1);
+			}
+		}
+
+		gc.setBackground(gc.getDevice().getSystemColor(SWT.COLOR_BLACK));
+		gc.fillRectangle(0, 0, width, height);
+
+		for (int i = 0; i < NUMBER_OF_STARS; i++) {
+			/* compute 3D position */
+			final int tempx = (int) (stars[i].xpos / stars[i].zpos + width / 2);
+			final int tempy = (int) (stars[i].ypos / stars[i].zpos + height / 2);
+
+			if (tempx >= 0 && tempx < width && tempy >= 0 && tempy < height) {
+				Color color = new Color(gc.getDevice(), stars[i].color, stars[i].color, stars[i].color);
+				gc.setForeground(color);
+				gc.drawPoint(tempx, tempy);
+				color.dispose();
+			}
+		}
+	}
+
+	private Star initStar(int i) {
+		final Star star = new Star();
+		star.xpos = (float) (-10.0 + 20.0 * Math.random());
+		star.ypos = (float) (-10.0 + 20.0 * Math.random());
+
+		star.xpos *= 3072.0; /* change viewpoint */
+		star.ypos *= 3072.0;
+
+		star.zpos = i;
+		star.speed = 2 + (int) (2.0 * Math.random());
+
+		star.color = i >> 2; /* the closer to the viewer the brighter */
+
+		return star;
+	}
+}