support computing decay duration independent of fromValue; fix facebo…

…okarchive#37
owenv · May 2, 2014 · 3b6eb6e · 3b6eb6e
1 parent ad03259
commit 3b6eb6e
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Showing 3 changed files with 71 additions and 3 deletions.
diff --git a/pop-tests/POPDecayAnimationTests.mm b/pop-tests/POPDecayAnimationTests.mm
@@ -459,4 +459,29 @@ - (void)testEndValueOnReuse
   STAssertTrue(lastValue > toValue, @"unexpected last value:%f");
 }
 
+- (void)testComputedProperties
+{
+  POPDecayAnimation *anim = [POPDecayAnimation animationWithPropertyNamed:kPOPLayerPositionX];
+
+  // set velocity, test duration
+  anim.velocity = @(100);
+  CGFloat d1 = anim.duration;
+  STAssertTrue(d1 > 0, @"unexpected duration %@", anim);
+
+  // set velocity, test duration
+  anim.velocity = @(1000);
+  CGFloat d2 = anim.duration;
+  STAssertTrue(d2 > d1, @"unexpected duration %@", anim);
+
+  // set from value, test to value
+  anim.fromValue = @(0);
+  CGFloat p1 = [anim.toValue floatValue];
+  STAssertTrue(p1 > [anim.fromValue floatValue], @"unexpected to value %@", anim);
+
+  // set from value, test to value
+  anim.fromValue = @(10000);
+  CGFloat p2 = [anim.toValue floatValue];
+  STAssertTrue(p2 > [anim.fromValue floatValue] && p2 > p1, @"unexpected to value %@", anim);
+}
+
 @end
diff --git a/pop/POPDecayAnimation.mm b/pop/POPDecayAnimation.mm
@@ -99,7 +99,8 @@ - (void)setVelocity:(id)aValue
 - (void)_ensureComputedProperties
 {
   if (NULL == __state->toVec) {
-    __state->computeDestinationValues();
+    __state->computeDuration();
+    __state->computeToValue();
   }
 }
 
@@ -113,11 +114,13 @@ - (void)_appendDescription:(NSMutableString *)s debug:(BOOL)debug
 {
   [super _appendDescription:s debug:debug];
 
-  if (NULL != __state->toVec)
+  if (0 != self.duration) {
     [s appendFormat:@"; duration = %f", self.duration];
+  }
 
-  if (__state->deceleration)
+  if (__state->deceleration) {
     [s appendFormat:@"; deceleration = %f", __state->deceleration];
+  }
 }
 
 @end
diff --git a/pop/POPDecayAnimationInternal.h b/pop/POPDecayAnimationInternal.h
@@ -64,6 +64,46 @@ struct _POPDecayAnimationState : _POPPropertyAnimationState
 
   }
 
+  void computeDuration() {
+
+    // compute duration till threshold velocity
+    Vector4r scaledVelocity = vector4(velocityVec) / 1000.;
+
+    double k = dynamicsThreshold * kPOPAnimationDecayMinimalVelocityFactor / 1000.;
+    double vx = k / scaledVelocity.x;
+    double vy = k / scaledVelocity.y;
+    double vz = k / scaledVelocity.z;
+    double vw = k / scaledVelocity.w;
+    double d = log(deceleration) * 1000.;
+    duration = MAX(MAX(MAX(log(fabs(vx)) / d, log(fabs(vy)) / d), log(fabs(vz)) / d), log(fabs(vw)) / d);
+
+    // ensure velocity threshold is exceeded
+    if (isnan(duration) || duration < 0) {
+      duration = 0;
+    }
+  }
+
+  void computeToValue() {
+    // to value assuming final velocity as a factor of dynamics threshold
+    // derived from v' = v * d^dt used in decay_position
+    // to compute the to value with maximal dt, p' = p + (v * d) / (1 - d)
+    VectorRef fromValue = NULL != currentVec ? currentVec : fromVec;
+    if (!fromValue) {
+      return;
+    }
+
+    // ensure duration is computed
+    if (0 == duration) {
+      computeDuration();
+    }
+
+    // compute to value
+    VectorRef toValue(Vector::new_vector(fromValue.get()));
+    Vector4r velocity = velocityVec->vector4r();
+    decay_position(toValue->data(), velocity.data(), valueCount, duration, deceleration);
+    toVec = toValue;
+  }
+
   void computeDestinationValues() {
     // to value assuming final velocity as a factor of dynamics threshold
     // derived from v' = v * d^dt used in decay_position