/// <summary>
/// Gets the cycle offset for a time value.
/// </summary>
/// <typeparam name="T">The type of animation value.</typeparam>
/// <param name="time">The time value.</param>
/// <param name="startTime">The start time.</param>
/// <param name="endTime">The end time.</param>
/// <param name="startValue">In: The animation value at <paramref name="startTime"/>.</param>
/// <param name="endValue">In: The animation value at <paramref name="endTime"/>.</param>
/// <param name="traits">The traits of the animation value.</param>
/// <param name="loopBehavior">The post-loop behavior.</param>
/// <param name="cycleOffset">
/// Out: The cycle offset.
/// </param>
/// <remarks>
/// The cycle offset is <see cref="IAnimationValueTraits{T}.SetIdentity"/> if the
/// <see cref="LoopBehavior"/> is unequal to <see cref="LoopBehavior.CycleOffset"/> or if the
/// <paramref name="time"/> is in the regular cycle (between the first and the last key frame).
/// </remarks>
internal static void GetCycleOffset <T>(TimeSpan time,
TimeSpan startTime, TimeSpan endTime,
ref T startValue, ref T endValue,
IAnimationValueTraits <T> traits,
LoopBehavior loopBehavior,
ref T cycleOffset)
{
Debug.Assert(endTime > startTime, "Invalid start and end time.");
TimeSpan length = endTime - startTime;
// Handle cycle offset.
if (loopBehavior == LoopBehavior.CycleOffset && length != TimeSpan.Zero)
{
traits.Invert(ref startValue, ref startValue);
traits.Add(ref startValue, ref endValue, ref cycleOffset);
if (time < startTime)
{
long numberOfPeriods = (time.Ticks - endTime.Ticks) / length.Ticks;
Debug.Assert(numberOfPeriods < 0, "Negative number of periods expected.");
traits.Multiply(ref cycleOffset, (int)numberOfPeriods, ref cycleOffset);
}
else if (time > endTime)
{
long numberOfPeriods = (time.Ticks - startTime.Ticks) / length.Ticks;
Debug.Assert(numberOfPeriods > 0, "Positive number of periods expected.");
traits.Multiply(ref cycleOffset, (int)numberOfPeriods, ref cycleOffset);
}
else
{
traits.SetIdentity(ref cycleOffset);
}
}
}
public static T Multiply <T>(this IAnimationValueTraits <T> traits, T value, int factor)
{
traits.Multiply(ref value, factor, ref value);
return(value);
}