| -api-id | -api-type |
|---|---|
T:Windows.UI.Composition.Interactions.InteractionTrackerInertiaMotion |
winrt class |
An ExpressionAnimation that defines motion of InteractionTracker during its inertia state.
The InteractionTrackerMotion class contains two ExpressionAnimations representing a second derivative equation of position InteractionTracker will use to define the motion from the start to end of inertia when a particular condition is met. The InteractionTrackerMotion class is defined as two parts: The conditional statement to define when the motion will take place and the equation that describes the motion for how InteractionTracker will reach its final resting position. Utilize the InteractionTrackerInertiaMotion class when you need to define a customized motion (such as a spring motion) for InteractionTracker to use when in its inertia state.
When building out the ExpressionAnimation for the motion component of InteractionTrackerInertiaMotion, the expression is described as a second derivative equation. For example, In the code snippet above, we utilize the basic equation for Spring Force motion with damping.
When attaching the InteractionTrackerInertiaMotion modifier to the InteractionTracker, you configure it to either the X/Y Position or Scale.
The ExpressionAnimation defining the condition property only gets evaluated once when InteractionTracker enters Inertia (aka when the interaction completes such as finger released). If the condition evaluates to true, the InertiaMotion Expression gets evaluated every frame for the remainder of Inertia, even if the condition expression technically is no longer true.
InteractionTrackerInertiaMotion modifiers change the equation InteractionTracker uses to calculate its position. Thus, the final resting position is determined by the nature of the equation itself. If you need InteractionTracker to stop at a specific location, utilize the InteractionTrackerInertiaRestingValue modifier.
void CustomSpringInertiaMotion(float dampingCoefficient, float springStiffnessCoefficient)
{
//
// Set up our inertia modifiers to use our custom motion
//
InteractionTrackerInertiaMotion[] modifiers =
new InteractionTrackerInertiaMotion[1];
var modifier1 = InteractionTrackerInertiaMotion.Create(_compositor);
/*
We create a custom spring motion for when the InteractionTracker passes the
maximum boundary.
When we hit the boundary, the amount of oscillation is determined by the distance to the far end point, the spring stiffness and damping rate.
*/
// Define the condition that the spring motion gets applied – when we pass the
// maximum boundary
modifier1.Condition = _compositor.CreateExpressionAnimation(
"this.Target.NaturalRestingPosition.X > this.Target.MaxPosition.X");
// Define the second derivative equation as a custom spring force motion
// Equation = kx–cv where (k is spring constant, c is damping, x is displacement)
modifier1.Motion = _compositor.CreateExpressionAnimation(
"(-springStiffnessCoefficient * (this.Target.Position.X – this.Target.MaxPosition.X)) + " +
"(-dampingCoefficient * target.PositionVelocityInPixelsPerSecond.X");
modifier1.Motion.SetScalarParameter("springStiffnessCoefficient", springStiffnessCoefficient);
modifier1.Motion.SetScalarParameter("dampingCoefficient", dampingCoefficient);
modifiers[0] = modifier1;
// Attach InertiaModifiers to the Y position component of InteractionTracker
_tracker.ConfigurePositionYInertiaModifiers(modifiers);
}