Difference Between LockScreen and RefreshViews

One of the Newton 2.x OS Q&As
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This document was exported on 7/23/97.

Difference Between LockScreen and RefreshViews (1/15/97)

Q: In the NPG, it states that sending a view the view:LockScreen(nil) message forces an "immediate update". How is this different from calling RefreshViews?

A: When you post drawing commands (for example, DrawShape) the system normally renders the shape on the screen immediately. :LockScreen(true) provides a way to "batch up" the screen updates for multiple drawing calls. Sending :LockScreen(nil) "unplugs" the temporary block that has been placed on the screen updater, causing all the batched drawing changes to be rendered on the LCD.

RefreshViews tells the system to execute the commands needed to draw every view that has a dirty region. You can think of it as working at a level "above" the screen lock routines. When you send the message Dirty, it does not immediately cause the system to redraw the dirtied view, instead it adds the view to the dirty area for later redrawing.

You could lock the screen, dirty a view with a SetValue, call RefreshViews (and not see an update) draw a few shapes, and then, when you unlock the screen, the refreshes to the dirty regions and your shapes will all appear at once.

A bit more detail on the interaction between LockScreen and RefreshViews:
1. Does LockScreen(nil) result in a RefreshViews?

No. LockScreen(true) just stops the hardware screen from updating from the offscreen buffer. LockScreen(nil) releases that lock which usually causes the hardware screen to update soon thereafter.

2. While the screen is locked, will SetValues draw into the offscreen buffer?

SetValue doesn't draw. Otherwise, see 1.

3. While the screen is locked, what is the result of calling RefreshViews?

It will draw any dirty views into the offscreen buffer.