By default, the Value property is empty. You can associate a value with a clipping object. For instance, let's say we define the value of a clipping rectangle as being its width. In other words, if we change the clip's Value property, the Width property of the ClipRectangle object is changed too, so the clipping rectangle will vary in its width. The same we can imagine the sweep angle or a pie or radius of a circle. The Change event notifies whether a layer is moved, rotated, so during this event we can call the clip's Value to update the clipping region on specified layer. 

For instance, let's say that we have the following:

and we want to clip the "Clip" layer, as soon as the "Thumb" is rotated like follows:

so you need to do the following:

• specify the "Thumb" to be rotatable, using the OnDrag property, like Layers.Item("Thumb").OnDrag = exDoRotate. In case we need to specify a different initial position of the layer, we can call the DefaultRotateAngle property, to specify another angle by default.
• specify the clipping zone for "Clip" layer to be a pie, such as Layers.Item("Clip").Clip.Pie.SweepAngle = "value", that specifies that the sweep angle of the clipping pie is controlled by the clip's Value property
• handle the Change event and call Layers.Item("Clip").Clip.Value = Layers.Item("Thumb").RotateAngle, which means that when any change occurs ( the "Thumb" is rotated ), change the Value of the Clip object of the "Clip" layer to be the rotate angle of the "Thumb" layer, so in other words as the clip's Value is associated with the sweep angle, change the sweep angle of the clipping pie to be the same as the rotation angle of the "Thumb" layer.

Now, let's say we want to remove the transparency on the "Clip" layer, so we need to add a new clipping object, this time of Picture object, with the same picture as:

• Layers("Clip").Clip.Picture.Name = Layers("Clip").Background.Picture.Name, which applies the clipping from the same picture, this time with no transparent pixels

so we get:

And if we hide a few intermediate layers we can get:

or if we add a new layer as a clone of others with a clipping pie we can get:

For instance, if you have: 

• Layers.Item("Clip").Clip.Value = 45, you actually clip as a pie for a 45 degree the "Clip" layer. 
• If using Layers("Clip").Clip.Pie.SweepAngle = "2 * value", it indicates that the angle of the clipping region is twice the rotation angle of the thumb.
• If using Layers("Clip").Clip.Pie.SweepAngle = "value / 2", it indicates that the angle of the clipping region is half of the rotation angle of the thumb.

Any of the following properties ( or combination of them ) can be used to do the clipping:

• Ellipse, clips the layer as a ellipse / circle
• Picture, clips the layer using a picture as a mask
• Pie, clips the layer as a arc / pie
• Polygon, clips the layer giving the points that define a polygon, triangle, rectangle, and so on
• Rectangle, clips the layer giving a rectangle
• RoundRectangle, clips the layer giving a round rectangle