Only load image resources when needed.

- Stop loading all images on startup.
- Game images are preloaded before the song starts.
- Destroy skin images immediately after finishing a beatmap, potentially saving lots of memory.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/GameImage.java

@@ -313,6 +313,11 @@ public enum GameImage {
 	 */
 	private static int containerWidth, containerHeight;
 
+	/**
+	 * Whether a skin image has been loaded.
+	 */
+	private static boolean skinImageLoaded = false;
+
 	/**
 	 * Initializes the GameImage class with container dimensions.
 	 * @param width the container width
@@ -323,6 +328,19 @@ public enum GameImage {
 		containerHeight = height;
 	}
 
+	/**
+	 * Destroys all skin images, if any have been loaded.
+	 */
+	public static void destroySkinImages() {
+		if (skinImageLoaded) {
+			for (GameImage img : GameImage.values()) {
+				if (img.isGameImage())
+					img.destroySkinImage();
+			}
+			skinImageLoaded = false;
+		}
+	}
+
 	/**
 	 * Constructor.
 	 * @param filename the image file name
@@ -353,6 +371,8 @@ public enum GameImage {
 	 * The skin image takes priority over the default image.
 	 */
 	public Image getImage() {
+		if (defaultImage == null)
+			setDefaultImage();
 		return (skinImage != null) ? skinImage : defaultImage;
 	}
 
@@ -369,13 +389,14 @@ public enum GameImage {
 
 	/**
 	 * Sets the default image for this resource.
+	 * If the default image has already been loaded, this will do nothing.
 	 */
 	public void setDefaultImage() {
+		if (defaultImage != null)
+			return;
 		try {
-			if (defaultImage != null && !defaultImage.isDestroyed())
-				defaultImage.destroy();
-
 			defaultImage = new Image(filename);
+			process();
 		} catch (SlickException e) {
 			Log.error(String.format("Failed to set default image '%s'.", filename), e);
 		}
@@ -387,15 +408,19 @@ public enum GameImage {
 	 * @return true if a new skin image is loaded, false otherwise
 	 */
 	public boolean setSkinImage(File dir) {
-		try {
-			// destroy the existing image, if any
-			if (skinImage != null && !skinImage.isDestroyed())
-				skinImage.destroy();
+		if (dir == null)
+			return false;
 
+		// destroy the existing image, if any
+		destroySkinImage();
+
+		try {
 			// set a new image
 			File file = new File(dir, filename);
 			if (file.isFile() && !Options.isBeatmapSkinIgnored()) {
 				skinImage = new Image(file.getAbsolutePath());
+				process();
+				skinImageLoaded = true;
 				return true;
 			} else {
 				skinImage = null;
@@ -407,6 +432,21 @@ public enum GameImage {
 		}
 	}
 
+	/**
+	 * Destroys the associated skin image, if any.
+	 */
+	private void destroySkinImage() {
+		if (skinImage == null)
+			return;
+		try {
+			if (!skinImage.isDestroyed())
+				skinImage.destroy();
+			skinImage = null;
+		} catch (SlickException e) {
+			Log.error(String.format("Failed to destroy skin image for '%s'.", this.name()), e);
+		}
+	}
+
 	/**
 	 * Sub-method for image processing actions (via an override).
 	 * @param img the image to process
@@ -421,7 +461,7 @@ public enum GameImage {
 	/**
 	 * Performs individual post-loading actions on the image.
 	 */
-	public void process() {
+	private void process() {
 		setImage(process_sub(getImage(), containerWidth, containerHeight));
 	}
 }

src/itdelatrisu/opsu/Utils.java

@@ -184,12 +184,8 @@ public class Utils {
 			Log.error("Failed to load fonts.", e);
 		}
 
-		// set default game images
+		// initialize game images
 		GameImage.init(width, height);
-		for (GameImage img : GameImage.values()) {
-			img.setDefaultImage();
-			img.process();
-		}
 
 		// initialize game mods
 		for (GameMod mod : GameMod.values())

src/itdelatrisu/opsu/states/Game.java

@@ -859,8 +859,10 @@ public class Game extends BasicGameState {
 		// set images
 		File parent = osu.getFile().getParentFile();
 		for (GameImage img : GameImage.values()) {
-			if (img.isGameImage() && img.setSkinImage(parent))
-				img.process();
+			if (img.isGameImage()) {
+				img.setDefaultImage();  // ensure that default image has been loaded
+				img.setSkinImage(parent);
+			}
 		}
 
 		// skip button

src/itdelatrisu/opsu/states/SongMenu.java

@@ -581,6 +581,9 @@ public class SongMenu extends BasicGameState {
 		// stop playing the theme song
 		if (MusicController.isThemePlaying() && focusNode != null)
 			MusicController.play(focusNode.osuFiles.get(focusNode.osuFileIndex), true);
+
+		// destroy skin images, if any
+		GameImage.destroySkinImages();
 	}
 
 	@Override