Migrate Plasma effect to Graphics Example

This PR migrates the Plasma effect from SWT-OldSchoolEffect
to the SWT Graphics Example.

Changes:
- Implemented PlasmaTab.java extending AnimatedGraphicsTab
- Registered the new tab in GraphicsExample.java
- Added descriptive strings to examples_graphics.properties

Contributes to #3189

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: vogella

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

@@ -193,3 +193,6 @@ RippleDescription=This is a miscellaneous demonstration that uses a displacement
 
 Blob=Blob
 BlobDescription=This is a miscellaneous demonstration of an animated metaball effect where multiple blobs move randomly and blend together when overlapping.
+
+Plasma=Plasma
+PlasmaDescription=This is a miscellaneous demonstration of an animated plasma effect using precomputed sine tables and a cycling color palette.

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

@@ -480,6 +480,7 @@ GraphicsTab[] createTabs() {
 		new PathTab(this),
 		new TransformReuseTab(this),
 		new PathReuseTab(this),
+		new PlasmaTab(this),
 	};
 }
 

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

@@ -0,0 +1,173 @@
+/*******************************************************************************
+ * Copyright (c) 2019 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:
+ *     Calogiuri Enzo Antonio (Insolit Dust) - Original Version
+ *     Laurent Caron (laurent.caron at gmail dot com) - Conversion to SWT
+ *     IBM Corporation - adaptation to GraphicsExample
+ *******************************************************************************/
+
+package org.eclipse.swt.examples.graphics;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.graphics.GC;
+import org.eclipse.swt.graphics.Image;
+import org.eclipse.swt.graphics.ImageData;
+import org.eclipse.swt.graphics.PaletteData;
+
+/**
+ * This tab displays an animated plasma effect using precomputed sine tables
+ * and a cycling color palette.
+ */
+public class PlasmaTab extends AnimatedGraphicsTab {
+
+	private static final int SIN_TABLE_SIZE = 1800;
+
+	private ImageData imageData;
+	private Image outputImage;
+	private int[] palette;
+	private final int[] sin = new int[SIN_TABLE_SIZE];
+	private int plasmaIndex = 1;
+	private int lastWidth;
+	private int lastHeight;
+
+	public PlasmaTab(GraphicsExample example) {
+		super(example);
+	}
+
+	@Override
+	public String getCategory() {
+		return GraphicsExample.getResourceString("Misc"); //$NON-NLS-1$
+	}
+
+	@Override
+	public String getText() {
+		return GraphicsExample.getResourceString("Plasma"); //$NON-NLS-1$
+	}
+
+	@Override
+	public String getDescription() {
+		return GraphicsExample.getResourceString("PlasmaDescription"); //$NON-NLS-1$
+	}
+
+	@Override
+	public int getInitialAnimationTime() {
+		return 10;
+	}
+
+	@Override
+	public void dispose() {
+		if (outputImage != null) {
+			outputImage.dispose();
+			outputImage = null;
+		}
+	}
+
+	@Override
+	public void next(int width, int height) {
+		if (palette == null) {
+			return;
+		}
+		if (width != lastWidth || height != lastHeight) {
+			init(width, height);
+		}
+		drawPlasma(width, height);
+	}
+
+	@Override
+	public void paint(GC gc, int width, int height) {
+		if (palette == null) {
+			init(width, height);
+		}
+
+		gc.setBackground(gc.getDevice().getSystemColor(SWT.COLOR_BLACK));
+		gc.fillRectangle(0, 0, width, height);
+
+		if (imageData == null) {
+			return;
+		}
+
+		if (outputImage != null) {
+			outputImage.dispose();
+		}
+		outputImage = new Image(gc.getDevice(), imageData);
+		gc.drawImage(outputImage, 0, 0);
+	}
+
+	private void init(int width, int height) {
+		lastWidth = width;
+		lastHeight = height;
+		createColors();
+		precomputeSin();
+		imageData = new ImageData(width, height, 24, new PaletteData(0xFF0000, 0xFF00, 0xFF));
+	}
+
+	private void createColors() {
+		palette = new int[256];
+		int r = 0, g = 0, b = 0;
+		for (int i = 0; i < 256; i++) {
+			palette[i] = 0;
+		}
+
+		for (int i = 0; i < 42; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			r++;
+		}
+		for (int i = 42; i < 84; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			g++;
+		}
+		for (int i = 84; i < 126; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			b++;
+		}
+		for (int i = 126; i < 168; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			r--;
+		}
+		for (int i = 168; i < 210; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			g--;
+		}
+		for (int i = 210; i < 252; i++) {
+			palette[i] = r << 18 | g << 10 | b << 2;
+			b--;
+		}
+	}
+
+	private void precomputeSin() {
+		for (int i = 0; i < SIN_TABLE_SIZE; i++) {
+			sin[i] = (int) (Math.cos(Math.PI * i / 180) * 1024);
+		}
+	}
+
+	private void drawPlasma(int width, int height) {
+		plasmaIndex += 2;
+		if (plasmaIndex > 360) {
+			plasmaIndex = 0;
+		}
+
+		for (int x = 0; x < width; x++) {
+			int ix1 = Math.abs(((x << 1) + (plasmaIndex >> 1)) % SIN_TABLE_SIZE);
+			int ix2 = Math.abs((x + (plasmaIndex << 1)) % SIN_TABLE_SIZE);
+			int ix3 = Math.abs(((x >> 1) + plasmaIndex) % SIN_TABLE_SIZE);
+			final int indexX = 75 + (sin[ix1] + sin[ix2] + (sin[ix3] << 1) >> 6);
+
+			for (int y = 0; y < height; y++) {
+				int iy1 = Math.abs((y + (plasmaIndex << 1)) % SIN_TABLE_SIZE);
+				int iy2 = Math.abs(((y << 1) + (plasmaIndex >> 1)) % SIN_TABLE_SIZE);
+				int iy3 = Math.abs((y + plasmaIndex) % SIN_TABLE_SIZE);
+				final int indexY = 75 + ((sin[iy1] << 1) + sin[iy2] + (sin[iy3] << 1) >> 5);
+				final int colorIndex = Math.abs((indexX * indexY >> 5) % 256);
+				imageData.setPixel(x, y, palette[colorIndex]);
+			}
+		}
+	}
+}