A ratio between the diameter of the cylinder and the viewport's size in the main axis.
A value of 1 means the cylinder has the same diameter as the viewport's size.
A value smaller than 1 means items at the edges of the cylinder are entirely contained inside the viewport.
A value larger than 1 means angles less than ±pi / 2 from the center of the cylinder are visible.
The same number of children will be visible in the viewport regardless of the diameterRatio. The number of children visible is based on the viewport's length along the main axis divided by the children's itemExtent. Then the children are evenly distributed along the visible angles up to ±pi / 2.
Just as it's impossible to stretch a paper to cover the an entire half of a cylinder's surface where the cylinder has the same diameter as the paper's length, choosing a diameterRatio smaller than pi will leave same gaps between the children.
Defaults to an arbitrary but aesthetically reasonable number of 2.0.
Must not be null and must be positive.
final double diameterRatio