Fast scrolling causes un-needed refreshings of the whole child of a ScrollPane.

Name: joT67522 Date: 08/22/97


1. Construct a Frame sub-class (we are talking about an application)
   with its default layout.
2. Construct a new ScrollPane object with the default constructor:
   'new ScrollPane()'.
3. Construct a new Canvas sub-class.
4. Draw on the canvas some graphical figures using the Graphics
   drawing API, also in coordinates beyond the shown area of the
   Frame so that the scroll bars will be created.
5. Scroll fas in any direction by continuously holding the button
   left button on any of the scroll bar's arrowed edges.
The Problem:
 When successive scrolling is requested, such that the canvas
 contents does not ends moving the increment amount before the
 next scrolling event is received, the whole
 canvas is refreshed, i.e. erased and redrawn again, what makes
 scrolling very inconvenient and very very slow.

 This behaved differently in JDK1.1Beta3. There was never a redraw
 of the whole canvas. I think that you have fixed some other bug
 regarding resources consumed during scrolling in the Beta3, but
 have brouht in another problem.

company - Softera , email - ###@###.###
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ronan.mandel@Eng 1997-10-23
After a validate(), ScrollPane redraws the whole
of the component it contains. This redraw is not
limited to the visible region of the component
within the viewport of the ScrollPane. If the
ScrollPane contains a large component it takes
ages to redraw, rather than the redraw being
proportional to the size of the ScrollPane.
This is a very inefficient implementation.
The ScrollPane should impose a clip region
defined by the viewport when it redraws the
component it contains.