Fix Particle opacity calculation.

litiengine/src/main/java/de/gurkenlabs/litiengine/graphics/emitters/particles/Particle.java

@@ -75,10 +75,8 @@ public abstract class Particle implements ITimeToLive {
   /**
    * Constructs a new particle.
    *
-   * @param width
-   *          the particle width in pixels
-   * @param height
-   *          the particle height in pixels
+   * @param width  the particle width in pixels
+   * @param height the particle height in pixels
    */
   public Particle(final float width, final float height) {
     this.setWidth(width);
@@ -97,13 +95,12 @@ public long getAliveTime() {
   /**
    * Gets the current bounding box of the particle, depending on its spawn location.
    *
-   * @param origin
-   *          the spawn location of this particle
+   * @param origin the spawn location of this particle
    * @return The Rectangular particle bounding box.
    */
   public Rectangle2D getBoundingBox(final Point2D origin) {
     return new Rectangle2D.Double(origin.getX() + this.getX(), origin.getY() + this.getY(),
-        this.getWidth(), this.getHeight());
+      this.getWidth(), this.getHeight());
   }
 
   public Collision getCollisionType() {
@@ -159,27 +156,26 @@ public boolean isAntiAliased() {
   }
 
   public float getOpacity() {
-    if (this.isFading() && this.getTimeToLive() > 0) {
-      return MathUtilities.clamp(
-          this.getColor().getAlpha() / 255f - (float) this.getAliveTime() / this.getTimeToLive(), 0,
-          1);
+    if (isFading() && getTimeToLive() > 0) {
+      float maxAlpha = getColor().getAlpha() / 255f;
+      float progress = (float) getAliveTime() / getTimeToLive();
+      return MathUtilities.clamp(maxAlpha - progress * maxAlpha, 0, 1);
     }
     return 1;
   }
 
   /**
    * Gets the location relative to the specified effect location.
    *
-   * @param effectLocation
-   *          the effect position
+   * @param effectLocation the effect position
    * @return the location
    */
   public Point2D getRenderLocation(Point2D effectLocation) {
     // if we have a camera, we need to render the particle relative to the
     // viewport
     Point2D newEffectLocation =
-        Game.screens() != null ? Game.world().camera().getViewportLocation(effectLocation)
-            : effectLocation;
+      Game.screens() != null ? Game.world().camera().getViewportLocation(effectLocation)
+        : effectLocation;
     return this.getAbsoluteLocation(newEffectLocation);
   }
 
@@ -228,11 +224,11 @@ public Particle setCollisionType(final Collision collisionType) {
   }
 
   /**
-   * Enabling this check can be very performance hungry and should be used with caution and only for a small amount of
-   * particles.
+   * Enabling this check can be very performance hungry and should be used with caution and only for
+   * a small amount of particles.
    *
-   * @param ccd
-   *          If set to true, the collision will be checked continuously by a ray-cast approximation.
+   * @param ccd If set to true, the collision will be checked continuously by a ray-cast
+   *            approximation.
    * @return This particle instance.
    */
   public Particle setContinuousCollision(boolean ccd) {
@@ -377,12 +373,11 @@ public boolean timeToLiveReached() {
   }
 
   /**
-   * Updates the effect's position, change in xCurrent, change in yCurrent, remaining lifetime, and color.
+   * Updates the effect's position, change in xCurrent, change in yCurrent, remaining lifetime, and
+   * color.
    *
-   * @param emitterOrigin
-   *          The current {@link Emitter} origin
-   * @param updateRatio
-   *          The update ratio for this particle.
+   * @param emitterOrigin The current {@link Emitter} origin
+   * @param updateRatio   The update ratio for this particle.
    */
   public void update(final Point2D emitterOrigin, final float updateRatio) {
     if (this.aliveTick == 0) {
@@ -427,10 +422,8 @@ public void update(final Point2D emitterOrigin, final float updateRatio) {
   /**
    * Test for ray cast collisions
    *
-   * @param emitterOrigin
-   *          The current {@link Emitter} origin
-   * @param updateRatio
-   *          The update ratio for this particle.
+   * @param emitterOrigin The current {@link Emitter} origin
+   * @param updateRatio   The update ratio for this particle.
    * @return True if ray cast collision occurs
    */
   protected boolean hasRayCastCollision(final Point2D emitterOrigin, final float updateRatio) {
@@ -467,12 +460,12 @@ private boolean checkForCollision(final Point2D emitterOrigin, float targetX, fl
       double endY = emitterOrigin.getY() + targetY;
       Line2D ray = new Line2D.Double(start.getX(), start.getY(), endX, endY);
       if (this.getCollisionType() != Collision.NONE && Game.physics() != null && Game.physics()
-          .collides(ray, this.getCollisionType())) {
+        .collides(ray, this.getCollisionType())) {
         collide();
         return true;
       }
     } else if (this.getCollisionType() != Collision.NONE && Game.physics() != null && Game.physics()
-        .collides(this.getBoundingBox(emitterOrigin).getBounds2D(), this.getCollisionType())) {
+      .collides(this.getBoundingBox(emitterOrigin).getBounds2D(), this.getCollisionType())) {
       collide();
       return true;
     }