Replaced all linear fade-out transitions with eased transitions.

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

src/org/newdawn/slick/state/transition/DelayedFadeOutTransition.java

@@ -39,6 +39,7 @@ public class DelayedFadeOutTransition implements Transition {
 	 * @param color The color we're going to fade out to
 	 * @param fadeTime The time it takes the fade to occur
 	 * @param delay The time before the fade starts (must be less than {@code fadeTime})
+	 * @throws IllegalArgumentException if {@code delay} is greater than {@code fadeTime}
 	 */
 	public DelayedFadeOutTransition(Color color, int fadeTime, int delay) {
 		if (delay > fadeTime)

src/org/newdawn/slick/state/transition/EasedFadeOutTransition.java

@@ -0,0 +1,83 @@
+package org.newdawn.slick.state.transition;
+
+import itdelatrisu.opsu.ui.animations.AnimationEquation;
+
+import org.newdawn.slick.Color;
+import org.newdawn.slick.GameContainer;
+import org.newdawn.slick.Graphics;
+import org.newdawn.slick.state.GameState;
+import org.newdawn.slick.state.StateBasedGame;
+
+/**
+ * A transition to fade out to a given colour using an easing function.
+ *
+ * @author kevin (base)
+ */
+public class EasedFadeOutTransition implements Transition {
+	/** The color to fade to */
+	private final Color color;
+	/** The time it takes the fade to happen */
+	private final int fadeTime;
+	/** The easing function */
+	private final AnimationEquation eq;
+	/** The transition progress */
+	private float t = 0f;
+
+	/**
+	 * Create a new eased fade out transition.
+	 */
+	public EasedFadeOutTransition() { this(Color.black, 500, AnimationEquation.OUT_QUART); }
+
+	/**
+	 * Create a new eased fade out transition.
+	 * 
+	 * @param color The color we're going to fade out to
+	 */
+	public EasedFadeOutTransition(Color color) { this(color, 500, AnimationEquation.OUT_QUART); }
+
+	/**
+	 * Create a new eased fade out transition.
+	 * 
+	 * @param color The color we're going to fade out to
+	 * @param fadeTime The time it takes the fade to occur
+	 */
+	public EasedFadeOutTransition(Color color, int fadeTime) { this(color, fadeTime, AnimationEquation.OUT_QUART); }
+
+	/**
+	 * Create a new eased fade out transition.
+	 * 
+	 * @param color The color we're going to fade out to
+	 * @param fadeTime The time it takes the fade to occur
+	 * @param eq The easing function to use
+	 */
+	public EasedFadeOutTransition(Color color, int fadeTime, AnimationEquation eq) {
+		this.color = new Color(color);
+		this.color.a = 0;
+		this.fadeTime = fadeTime;
+		this.eq = eq;
+	}
+
+	@Override
+	public boolean isComplete() { return (color.a >= 1); }
+
+	@Override
+	public void postRender(StateBasedGame game, GameContainer container, Graphics g) {
+		Color old = g.getColor();
+		g.setColor(color);
+		g.fillRect(0, 0, container.getWidth() * 2, container.getHeight() * 2);
+		g.setColor(old);
+	}
+
+	@Override
+	public void update(StateBasedGame game, GameContainer container, int delta) {
+		t += delta * (1.0f / fadeTime);
+		float alpha = t > 1f ? 1f : eq.calc(t);
+		color.a = alpha;
+	}
+
+	@Override
+	public void preRender(StateBasedGame game, GameContainer container, Graphics g) {}
+
+	@Override
+	public void init(GameState firstState, GameState secondState) {}
+}