Allow the start or end alpha levels to be outside the normal range so that

useful delays can be built into the beginning or end of the animation.
Detect bogus parameters in the constructor and throw an exception to
save developer head-scratching time when the animation doesn't actually
do any fading.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3560 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/media/effects/FadeEffect.java

@@ -32,24 +32,32 @@ public class FadeEffect
 {
     public FadeEffect (float alpha, float step, float target)
     {
+        if ((step == 0f) || (alpha > target && step > 0f) ||
+                (alpha < target && step < 0f)) {
+            throw new IllegalArgumentException("Step specified is illegal: " +
+                "Fade would never finish (start=" + alpha + ", step=" + step +
+                ", target=" + target + ")");
+        }
+
         // save things off
-        _startAlpha = _alpha = Math.max(alpha, 0.0f);
+        _startAlpha = alpha; 
         _step = step;
-        _target = Math.min(target, 1.0f);
+        _target = target;
 
         // create the initial composite
+        _alpha = Math.max(0f, Math.min(1f, _startAlpha));
         _comp = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, _alpha);
     }
 
     public void init (long tickStamp)
     {
+        _finished = false;
         _initStamp = tickStamp;
     }
 
     public boolean finished ()
     {
-        return (_startAlpha < _target) ?
-            (_alpha >= _target) : (_alpha <= _target);
+        return _finished;
     }
 
     public float getAlpha ()
@@ -62,6 +70,8 @@ public class FadeEffect
         // figure out the current alpha
         long msecs = tickStamp - _initStamp;
         float alpha = _startAlpha + (msecs * _step);
+        _finished = (_startAlpha < _target) ? (alpha >= _target)
+                                            : (alpha <= _target);
         if (alpha < 0.0f) {
             alpha = 0.0f;
         } else if (alpha > 1.0f) {
@@ -74,7 +84,8 @@ public class FadeEffect
             return true;
         }
 
-        return false;
+        // return false, unless we're finished
+        return _finished;
     }
 
     public void beforePaint (Graphics2D gfx)
@@ -108,4 +119,7 @@ public class FadeEffect
 
     /** Time zero. */
     protected long _initStamp;
+
+    /** True when we're finished. */
+    protected boolean _finished;
 }