private void CompositionTarget_Rendering(object sender, EventArgs e)
{
if (AssociatedObject == null || !AssociatedObject.IsVisible)
{
return;
}
if (currentInteractionStatus == InteractionStatus.PreEngaged)
{
PreEngagementAnimationHelper.Update();
}
if (currentInteractionStatus != InteractionStatus.Scrolling)
{
return;
}
UpdateSnapAnimation();
if (CurrentForce <= 0 && (Convert.ToInt32(AssociatedObject.ScrollPosition % MaximumDegreeReturnSnap) == 0) && isSnapAnimationCompleted)
{
currentInteractionStatus = InteractionStatus.None;
return;
}
var currentTime = DateTime.Now;
var elapsedTime = currentTime - LastUpdate;
CurrentVelocity = CurrentForce / BodyMass;
var dueDisplacement = CurrentVelocity * (Double)elapsedTime.TotalMilliseconds;
if (CurrentForceDirection == ForceDirection.Down)
{
dueDisplacement *= -1;
}
var newOffset = AssociatedObject.ScrollPosition + dueDisplacement;
if (Double.IsNaN(newOffset))
{
return;
}
AssociatedObject.ScrollPosition = newOffset;
CurrentForce = Math.Max(0, CurrentForce - ((Double)elapsedTime.TotalMilliseconds * CurrentForce * Friction));
if (CurrentForce < 0.0001)
{
CurrentForce = 0;
}
if (!isSnapAnimationCompleted)
{
return;
}
if (CurrentVelocity <= SnapVelocity)
{
var roundedOffset = Math.Round(newOffset, 0);
var goalOffset = GetSnapOffset(roundedOffset);
CurrentForce = 0;
StartSnapAnimation(AssociatedObject.ScrollPosition, goalOffset);
}
LastUpdate = DateTime.Now;
}
private void UpdateSnapAnimation()
{
SnapAnimationHelper.Update();
}