[haiku-bugs] Re: [Haiku] #9457: API for Obtaining Cursor Shape Bitmap and Change Notification
- From: "AGMS" <trac@xxxxxxxxxxxx>
- Date: Thu, 14 Feb 2013 17:21:28 -0000
#9457: API for Obtaining Cursor Shape Bitmap and Change Notification
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Reporter: AGMS | Owner: axeld
Type: enhancement | Status: new
Priority: normal | Milestone: R1
Component: Servers/app_server | Version: R1/Development
Resolution: | Keywords: cursor, vnc
Blocked By: | Blocking:
Has a Patch: 0 | Platform: All
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Comment (by AGMS):
A simpler and very fast way of passing around the dirty rectangles would
be to have a global fixed size array of rectangles (used as a circular
buffer) and a global counter identifying the next rectangle to be written
by the app_server. Client programs have their own copy of the counter to
keep track of where they are in the rectangle list. So that clients can
detect missing too many updates (missed more than the array size), the
app_server just keeps on incrementing the counter up to infinity.
Everyone would use the count modulo the array size for indexing the array
(so the array should be a power of two in size).
No need for a separate update thread or the worry about lost BMessages
when activity gets too intense. For safety, the array and counter would
be in a read only memory area for the clients. An atomic add/fetch would
be used to update/read the counter and the app_server would write the new
rectangle before updating the counter.
It does mean that the clients would be polling the counter to check for
rectangles, rather than getting a callback or BMessage when there's a new
rectangle. But most of these clients would be doing an update of some
sort every frame anyway.
--
Ticket URL: <http://dev.haiku-os.org/ticket/9457#comment:4>
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