private void ActivateSpringForce()
{
var dampingConstant = 5;
var springConstant = 20;
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
// Set the condition to true (always)
modifier.SetCondition((BooleanNode)true);
// Define a spring-like force, anchored at position 0.
var target = ExpressionValues.Target.CreateInteractionTrackerTarget();
modifier.SetMotion((-target.Position.Y * springConstant) - (dampingConstant * target.PositionVelocityInPixelsPerSecond.Y));
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
private void ActivateSpringForce(float pullToRefreshDistance)
{
var dampingConstant = 5;
var springConstant = 5;
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
// Set the condition to true (always)
modifier.SetCondition((BooleanNode)true);
var target = ExpressionValues.Target.CreateInteractionTrackerTarget();
// Define a spring-like force, anchored at position 0. This brings the listView back to position 0.
modifier.SetMotion(-(target.Position.Y * springConstant) - (target.PositionVelocityInPixelsPerSecond.Y * dampingConstant));
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
private void ActivateSpringForce()
{
var dampingConstant = 5;
var springConstant = 20;
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
// Set the condition to true (always)
modifier.Condition = _compositor.CreateExpressionAnimation("true");
// Define a spring-like force, anchored at position 0.
modifier.Motion = _compositor.CreateExpressionAnimation(@"(-(this.target.Position.Y) * springConstant) - (dampingConstant * this.target.PositionVelocityInPixelsPerSecond.Y)");
modifier.Motion.SetScalarParameter("dampingConstant", dampingConstant);
modifier.Motion.SetScalarParameter("springConstant", springConstant);
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
private void ActivateGravityForce()
{
var gravity = -700;
var bounce = -150f;
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
modifier.Condition = _compositor.CreateExpressionAnimation("true");
modifier.Motion = _compositor.CreateExpressionAnimation(
"(this.target.Position.Y > 0) ? (gravity) :" +
"((this.target.PositionVelocityInPixelsPerSecond.Y <= 0) ?" +
"(bounce * this.target.PositionVelocityInPixelsPerSecond.Y) : (0))");
modifier.Motion.SetScalarParameter("gravity", gravity);
modifier.Motion.SetScalarParameter("bounce", bounce);
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
private void ActivateSpringForce()
{
#if SDKVERSION_15063
//
// On newer builds, use the Spring NaturalMotion
//
if (MainPage.RuntimeCapabilities.IsSdkVersionRuntimeSupported(RuntimeSupportedSDKs.SDKVERSION._15063))
{
var modifier = InteractionTrackerInertiaNaturalMotion.Create(_compositor);
var springAnimation = _compositor.CreateSpringScalarAnimation();
springAnimation.Period = TimeSpan.FromSeconds(.15);
springAnimation.DampingRatio = .4f;
springAnimation.FinalValue = 0.0f;
modifier.Condition = _compositor.CreateExpressionAnimation("true");
modifier.NaturalMotion = springAnimation;
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
//
// On older builds, use a custom force that behaves like a spring
//
else
#endif
{
var dampingConstant = 5;
var springConstant = 20;
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
// Set the condition to true (always)
modifier.SetCondition((BooleanNode)true);
// Define a spring-like force, anchored at position 0.
var target = ExpressionValues.Target.CreateInteractionTrackerTarget();
modifier.SetMotion((-target.Position.Y * springConstant) - (dampingConstant * target.PositionVelocityInPixelsPerSecond.Y));
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
}
private void ActivateGravityForce()
{
//
// Setup the gravity+bounce inertia modifier.
//
string posY = "this.target.Position.Y";
string velY = "this.target.PositionVelocityInPixelsPerSecond.Y";
//
// Gravity Force
//
// Adding a factor of 100 since -9.8 pixels / second ^2 is not very fast.
var gravity = -9.8f * 100;
// Always on.
string gravityForce = "gravity";
//
// Floor Force
//
// This is the force that resists gravity and causes the bouncing. It's defined as:
// 1. Zero if above the floor,
// 2. Equal and opposite to gravity if "on" the floor (1 pixel above floor or below),
// 3. The effects of 2., plus a reflective force if the direction of motion is still downward and the tracker is below the floor.
// This force is at its strongest (-1.8 * 100 * V) if the tracker is 5 or more
// pixels below floor, and weakest (-1.0 * 100 * V) if the tracker is "at" the
// floor.
//
// The amount the tracker is below the floor, capped to at most 5 below.
string amountBelowFloor = $"clamp(0, ({0} - {posY}), 5)";
// The time slice our force engine uses.
float dt = .01f;
//
// Defining bounce constants.
// -2 would cause perfectly inellastic reflection, bouncing as high as it fell from.
// -1 would cause perfectly ellastic reflection, freezing motion.
// We want some bounce, but we also want the bouncing to decay, so choose
// bounce factors between -1 and -2.
//
// Also, divide by the time slice width to make this reflective force apply entirely
// all at once.
//
var weakestBounce = -1.1f / dt;
var strongestBounce = -1.8f / dt;
string floorForce =
/*2.*/ $"(({posY} < ({0} + 1)) ? -gravity : 0) + " +
/*3.*/ $"((({velY} < 0) && ({posY} < {0})) ? lerp({weakestBounce}, {strongestBounce}, ({amountBelowFloor} / 5)) * {velY} : 0)";
//
// Apply the forces to the modifier
//
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
modifier.Condition = _compositor.CreateExpressionAnimation("true");
modifier.Motion = _compositor.CreateExpressionAnimation($"{gravityForce} + {floorForce}");
modifier.Motion.SetScalarParameter("gravity", gravity);
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}
/// <summary>
/// Use the value of specified ExpressionNode to dictate the motion for this inertia modifier.
/// </summary>
/// <param name="modifier">The modifier.</param>
/// <param name="expressionNode">The root ExpressionNode that represents the ExpressionAnimation.</param>
public static void SetMotion(this InteractionTrackerInertiaMotion modifier, ExpressionNode expressionNode)
{
modifier.Motion = CreateExpressionAnimationFromNode(modifier.Compositor, expressionNode);
}
private void ActivateGravityForce()
{
//
// Setup the gravity+bounce inertia modifier.
//
var target = ExpressionValues.Target.CreateInteractionTrackerTarget();
var posY = target.Position.Y;
var velY = target.PositionVelocityInPixelsPerSecond.Y;
//
// Gravity Force
//
// Adding a factor of 100 since -9.8 pixels / second ^2 is not very fast.
var gravity = -9.8f * 100;
//
// Floor Force
//
// This is the force that resists gravity and causes the bouncing. It's defined as:
// 1. Zero if above the floor,
// 2. Equal and opposite to gravity if "on" the floor (1 pixel above floor or below),
// 3. The effects of 2., plus a reflective force if the direction of motion is still downward and the tracker is below the floor.
// This force is at its strongest (-1.8 * 100 * V) if the tracker is 5 or more
// pixels below floor, and weakest (-1.0 * 100 * V) if the tracker is "at" the
// floor.
//
// The amount the tracker is below the floor, capped to at most 5 below.
var belowFloor = EF.Clamp(0, 0 - posY, 5);
// The time slice our force engine uses.
float dt = .01f;
//
// Defining bounce constants.
// -2 would cause perfectly inellastic reflection, bouncing as high as it fell from.
// -1 would cause perfectly ellastic reflection, freezing motion.
// We want some bounce, but we also want the bouncing to decay, so choose
// bounce factors between -1 and -2.
//
// Also, divide by the time slice width to make this reflective force apply entirely
// all at once.
//
var weakestBounce = -1.1f / dt;
var strongestBounce = -1.8f / dt;
var floorForceExpression = EF.Conditional(posY < 1,
-gravity,
0) +
EF.Conditional(EF.And(velY < 0f, posY < 0f),
EF.Lerp(weakestBounce, strongestBounce, belowFloor / 5) * velY,
0);
//
// Apply the forces to the modifier
//
var modifier = InteractionTrackerInertiaMotion.Create(_compositor);
modifier.SetCondition((BooleanNode)true);
modifier.SetMotion(gravity + floorForceExpression);
_tracker.ConfigurePositionYInertiaModifiers(new InteractionTrackerInertiaModifier[] { modifier });
}