Bounds, Wheel, and Resize

This guide covers the knobs that make ZoomBorder feel predictable in real applications.

Bounds Modes

BoundsMode controls how the viewport is constrained:

Unrestricted
KeepContentVisible
FillViewport
KeepCentered
Custom

Additional supporting properties:

BoundsPadding
MinimumVisibleContentPercentage
EnableConstrains

Use Custom when a subclass overrides GetContentBounds() or ValidateTransform(...). The returned rectangle is expressed in child content coordinates and drives both pan constraints and logical scrollbar extent. See Custom Bounds, Resize, and Rotation for a large-workspace example.

Wheel Behavior

Wheel input is configurable instead of being hard-coded:

zoomBorder.WheelBehavior = WheelBehaviorMode.Zoom;
zoomBorder.WheelWithCtrl = WheelBehaviorMode.Zoom;
zoomBorder.WheelWithShift = WheelBehaviorMode.PanHorizontal;
zoomBorder.WheelZoomSensitivity = 1.0;
zoomBorder.WheelPanSensitivity = 1.0;

This is useful when a surface needs horizontal scrolling, precision zoom, or different modifier semantics.

Resize Behavior

Resize handling is controlled by ResizeBehavior:

None
MaintainCenter
MaintainTopLeft
MaintainZoom
ReapplyStretch
Custom

Choose ReapplyStretch when the control should behave like a viewer that always re-fits content after host layout changes.

Dynamic Zoom Limits

Auto-calculated zoom limits are available through:

AutoCalculateMinZoom
AutoCalculateMaxZoom
MaxZoomPixelSize

That keeps very small or very large content usable without manually tuning MinZoomX, MaxZoomX, MinZoomY, and MaxZoomY for every surface.