Add opacity to textpane backgrounds

Also fix an invalid default option for the "background option"

ui_swing/plugin.config

     showfulltopic=false
     hideEmptyTopicBar=false
     textpanebackground=
-    textpanebackgroundoption=STRETCH
+    textpanebackgroundoption=SCALE
+    textpanebackgroundopacity=1
     desktopbackground=dmdirc://com/dmdirc/res/background.png
     desktopbackgroundoption=CENTER
     showjrewarning=true

ui_swing/src/com/dmdirc/addons/ui_swing/UIUtilities.java

 import com.dmdirc.addons.ui_swing.components.SupplierLoggingSwingWorker;
 import com.dmdirc.util.colours.Colour;
 
+import java.awt.AlphaComposite;
 import java.awt.Color;
+import java.awt.Composite;
 import java.awt.Font;
 import java.awt.FontMetrics;
 import java.awt.Graphics2D;
      * @param bounds           Bounds to paint within
      * @param backgroundImage  background image
      * @param backgroundOption How to draw the background
+     * @param opacity          Opacity of the image
      */
     public static void paintBackground(final Graphics2D g,
             final Rectangle bounds,
             final Image backgroundImage,
-            final BackgroundOption backgroundOption) {
+            final BackgroundOption backgroundOption,
+            final float opacity) {
         if (backgroundImage == null) {
             paintNoBackground(g, bounds);
         } else {
             switch (backgroundOption) {
                 case TILED:
-                    paintTiledBackground(g, bounds, backgroundImage);
+                    paintTiledBackground(g, bounds, backgroundImage, opacity);
                     break;
                 case SCALE:
-                    paintStretchedBackground(g, bounds, backgroundImage);
+                    paintStretchedBackground(g, bounds, backgroundImage, opacity);
                     break;
                 case SCALE_ASPECT_RATIO:
-                    paintStretchedAspectRatioBackground(g, bounds, backgroundImage);
+                    paintStretchedAspectRatioBackground(g, bounds, backgroundImage, opacity);
                     break;
                 case CENTER:
-                    paintCenterBackground(g, bounds, backgroundImage);
+                    paintCenterBackground(g, bounds, backgroundImage, opacity);
                     break;
                 default:
                     break;
     }
 
     private static void paintStretchedBackground(final Graphics2D g,
-            final Rectangle bounds, final Image backgroundImage) {
+            final Rectangle bounds, final Image backgroundImage, final float opacity) {
+        final Composite originalComposite = g.getComposite();
+        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
         g.drawImage(backgroundImage, 0, 0, bounds.width, bounds.height, null);
+        g.setComposite(originalComposite);
     }
 
     private static void paintCenterBackground(final Graphics2D g,
-            final Rectangle bounds, final Image backgroundImage) {
+            final Rectangle bounds, final Image backgroundImage, final float opacity) {
         final int x = bounds.width / 2 - backgroundImage.getWidth(null) / 2;
         final int y = bounds.height / 2 - backgroundImage.getHeight(null) / 2;
+        final Composite originalComposite = g.getComposite();
+        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
         g.drawImage(backgroundImage, x, y, backgroundImage.getWidth(null),
                 backgroundImage.getHeight(null), null);
+        g.setComposite(originalComposite);
     }
 
     private static void paintStretchedAspectRatioBackground(final Graphics2D g,
-            final Rectangle bounds, final Image backgroundImage) {
+            final Rectangle bounds, final Image backgroundImage, final float opacity) {
         final double widthratio = bounds.width
                 / (double) backgroundImage.getWidth(null);
         final double heightratio = bounds.height
 
         final int x = bounds.width / 2 - width / 2;
         final int y = bounds.height / 2 - height / 2;
+        final Composite originalComposite = g.getComposite();
+        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
         g.drawImage(backgroundImage, x, y, width, height, null);
+        g.setComposite(originalComposite);
     }
 
     private static void paintTiledBackground(final Graphics2D g,
-            final Rectangle bounds, final Image backgroundImage) {
+            final Rectangle bounds, final Image backgroundImage, final float opacity) {
         final int width = backgroundImage.getWidth(null);
         final int height = backgroundImage.getHeight(null);
 
             return;
         }
 
+        final Composite originalComposite = g.getComposite();
+        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opacity));
         for (int x = 0; x < bounds.width; x += width) {
             for (int y = 0; y < bounds.height; y += height) {
                 g.drawImage(backgroundImage, x, y, width, height, null);
             }
         }
+        g.setComposite(originalComposite);
     }
 
     /**

ui_swing/src/com/dmdirc/addons/ui_swing/textpane/BackgroundPainter.java

      */
     @Nonnull
     private final String optionKey;
+    /**
+     * Key in the domain to get image opacity level.
+     */
+    @Nonnull
+    private final String opacityKey;
+
     /** The URL builder to use to find icons. */
     private final URLBuilder urlBuilder;
     /**
      * Background option type.
      */
     private BackgroundOption backgroundOption;
+    /**
+     * Background opacity.
+     */
+    private float opacity;
 
     /**
      * Creates a new background painter.
      * @param domain        Domain to retrieve settings from
      * @param imageKey      Key for background image
      * @param optionKey     Key for background type
+     * @param opacityKey    Key for the opacity
      */
     public BackgroundPainter(
             final AggregateConfigProvider configManager,
             final URLBuilder urlBuilder,
             @Nonnull final String domain, @Nonnull final String imageKey,
-            @Nonnull final String optionKey) {
+            @Nonnull final String optionKey, @Nonnull final String opacityKey) {
         this.configManager = configManager;
         this.urlBuilder = urlBuilder;
         this.domain = domain;
         this.imageKey = imageKey;
         this.optionKey = optionKey;
+        this.opacityKey = opacityKey;
         configManager.getBinder().bind(this, BackgroundPainter.class);
     }
 
         return optionKey;
     }
 
+    @Nonnull
+    protected String getOpacityKey() {
+        return opacityKey;
+    }
+
     protected void setBackgroundImage(final Image backgroundImage) {
         this.backgroundImage = backgroundImage;
     }
         }
     }
 
+    @ConfigBinding(domain = "plugin-ui_swing", key = "textpanebackgroundopacity")
+    public void updateOpacity(final String opacity) {
+        try {
+            this.opacity = Float.valueOf(opacity);
+            if (this.opacity < 0 || this.opacity > 1) {
+                this.opacity = 1;
+            }
+        } catch (IllegalArgumentException ex) {
+            this.opacity = 1;
+        }
+    }
+
     @Override
     public void paint(final Graphics graphics, final JComponent component) {
         final Graphics2D g2 = (Graphics2D) graphics;
         g2.setColor(component.getBackground());
         g2.fill(g2.getClipBounds());
         UIUtilities.paintBackground(g2, component.getBounds(),
-                backgroundImage, backgroundOption);
+                backgroundImage, backgroundOption, opacity);
         super.paint(graphics, component);
     }
 

ui_swing/src/com/dmdirc/addons/ui_swing/textpane/TextPane.java

         setLayout(new MigLayout("fill, hidemode 3"));
         backgroundPainter = new BackgroundPainter(frame.getContainer().getConfigManager(),
                 urlBuilder, configDomain, "textpanebackground",
-                "textpanebackgroundoption");
+                "textpanebackgroundoption", "textpanebackgroundopacity");
         canvas = new TextPaneCanvas(this,
                 new CachingDocument<>(document, new AttributedStringMessageMaker()));
         final JLayer<JComponent> layer = new JLayer<>(canvas);