Components that display logical rows or columns should compute the scroll increment that will completely expose one block of rows or columns, depending on the value of orientation.

Scrolling containers, like JScrollPane, will use this method each time the user requests a block scroll.

Parameters:

visibleRect     The view area visible within the viewport

orientation     Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.

direction     Less than zero to scroll up/left, greater than zero for down/right.

Returns: The "block" increment for scrolling in the specified direction. This value should always be positive.

`visibleRect`		The view area visible within the viewport
`orientation`		Either SwingConstants.VERTICAL or SwingConstants.HORIZONTAL.
`direction`		Less than zero to scroll up/left, greater than zero for down/right.