[openbeosmediakit] BroadcastNewParameterValue - issues, solutions?

  • From: "David Shipman" <unlyrn@xxxxxxxxxxxxxxx>
  • To: openbeosmediakit@xxxxxxxxxxxxx
  • Date: Sun, 11 Aug 2002 11:20:15 NZST (+1200)

Hi all...

I'm currently finishing off the interface code for the system mixer 
addon, and thought it would be an opportune time to address a concern 
regarding BControllable nodes and the way their interfaces are updated.

Currently, many nodes will not update their display in accordance with 
parameter values changing - that is, if you change the value by some 
other method (another app, a different view of the same controls, etc), 
the controls will not move.
Only nodes that implement BroadcastNewParameterValue() in their 
SetParameterValue function update correctly - Be's Audio Mixer is an 
example of one such node.

However, there are (I feel) significant problems with this solution. At 
the very least, it means SetParameterValue is called twice for every 
update - once for the initial value, and then again when the broadcast 
is received. If you have several views open representing the same 
controls, the situation is even worse - it will send a Broadcast 
message for each view!

In certain conditions (such as when there are 3 or 4 views open to the 
same control), the Broadcast messages will become slightly delayed, 
resulting in a constant loop of updating parameter values - try it some 
time, its a real mess!

According to the BeBook, in the MediaTheme section -
" if an application uses MakeControlFor() to create individual controls 
rather than letting ViewFor() set up the entire view, the application 
assumes responsibility for setting the control's value in response to 
value change messages. "

I presume this to mean that the BMediaTheme returns handling code for 
changing parameter values - so a possible solution would be to use 
MediaThemes that set the display directly, rather than calling SetValue 
(and triggering another round of updates...)

Any thoughts, suggestions=3F

David Shipman

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