PanVelocity ComputeEdgeScrollVelocity(
Point dragPoint)
{
bool isHorizontalScrollAllowed = false;
bool isVerticalScrollAllowed = false;
var velocity = new PanVelocity();
// See in which directions we've enabled panning.
if (m_tpScrollViewer != null)
{
ScrollMode verticalScrollMode = ScrollMode.Disabled;
ScrollMode horizontalScrollMode = ScrollMode.Disabled;
verticalScrollMode = (m_tpScrollViewer.VerticalScrollMode);
horizontalScrollMode = (m_tpScrollViewer.HorizontalScrollMode);
isVerticalScrollAllowed = verticalScrollMode != ScrollMode.Disabled;
isHorizontalScrollAllowed = horizontalScrollMode != ScrollMode.Disabled;
if (isHorizontalScrollAllowed)
{
double offset = 0.0;
double bound = 0.0;
offset = (m_tpScrollViewer.HorizontalOffset);
// Try scrolling left.
velocity.HorizontalVelocity = ComputeEdgeScrollVelocityFromEdgeDistance(dragPoint.X);
if (velocity.IsStationary())
{
// Try scrolling right.
double width = ActualWidth;
velocity.HorizontalVelocity = -ComputeEdgeScrollVelocityFromEdgeDistance(width - dragPoint.X);
bound = (m_tpScrollViewer.ScrollableWidth);
}
else
{
// We're scrolling to the left.
// The minimum horizontal offset obtained here accounts for the presence of the
// sentinel offset values in the left padding and/or header case. For instance,
// with no header or padding this will return exactly 2.0.
bound = (m_tpScrollViewer.MinHorizontalOffset);
}
// Disallow edge scrolling if we're right up against the edge.
if (DoubleUtil.AreWithinTolerance(bound, offset, /*ScrollViewerScrollRoundingTolerance*/ 0.05))
{
velocity.Clear();
}
}
if (isVerticalScrollAllowed && velocity.IsStationary() /* only allow vertical edge scrolling if there is no horizontal edge scrolling */)
{
double offset = 0.0;
double bound = 0.0;
offset = m_tpScrollViewer.VerticalOffset;
// Try scrolling up.
velocity.VerticalVelocity = ComputeEdgeScrollVelocityFromEdgeDistance(dragPoint.Y);
if (velocity.IsStationary())
{
// Try scrolling down.
double height = ActualHeight;
velocity.VerticalVelocity = -ComputeEdgeScrollVelocityFromEdgeDistance(height - dragPoint.Y);
bound = (m_tpScrollViewer.ScrollableHeight);
}
else
{
// We're scrolling up.
// The minimum vertical offset obtained here accounts for the presence of the
// sentinel offset values in the top padding and/or header case. For instance,
// with no header or padding this will return exactly 2.0.
bound = m_tpScrollViewer.MinVerticalOffset;
}
// Disallow edge scrolling if we're right up against the edge.
if (DoubleUtil.AreWithinTolerance(bound, offset, /*ScrollViewerScrollRoundingTolerance*/ 0.05))
{
velocity.Clear();
}
}
}
return(velocity);
}