Visual Basic 6 Black Book:Working With Graphics
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Layering Graphics With The AutoRedraw And ClipControls Properties
When you create graphics in Visual Basic, bear in mind that graphical controls and labels, nongraphical controls, and graphics methods appear on different layers. The behavior of these layers depends on three things: the AutoRedraw property, the ClipControls property, and whether graphics methods appear inside or outside the Paint event. Usually the layers of a form or other container are as follows:

•  Front layer—Nongraphical controls like command buttons, checkboxes, and file controls.
•  Middle layer—Graphical controls and labels.
•  Back layer—Drawing space for the form or container. This is where the results of graphics methods appear.

Anything in one layer covers anything in the layer behind it, so graphics you create with the graphical controls appear behind the other controls on the form, and all graphics you create with the graphics methods appear below all graphical and nongraphical controls. Combining settings for AutoRedraw and ClipControls and placing graphics methods inside or outside the Paint event affects layering and the performance of the application. You can find the effects created by different combinations of AutoRedraw and ClipControls and placement of graphics methods in Table 18.3.
Table 18.3 Layering with AutoRedraw and ClipControls.

AutoRedraw
ClipControls
Methods In/Out Paint Event
Description

True
True (default)
Paint event ignored
Normal layering.

True
False
Paint event ignored
Normal layering. Forms with many controls that do not overlap may paint faster because no clipping region is calculated or created.

False (default)
True (default)
In
Normal layering.

False
True
Out
Nongraphical controls in front. Graphics methods and graphical controls appear mixed in the middle and back layers. Not recommended by Microsoft.

False
False
In
Normal layering, affecting only pixels that were previously covered or that appear when resizing a form.

False
False
Out
Graphics methods and all controls appear mixed in the three layers. Not recommended by Microsoft.





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