Hello Michael,
On 02/10/2011 03:57 AM, Michael Raab wrote:
> we have the need to add a timer value to some shaders, that gets updated each
> frame. I was thinking about how this can be done without addtional overhead
> and found out that there are some special shader parameters like
> OSGWorldMatrix that get updated each frame automatically.
> In my opinion adding an additional special parameter like OSGSystemTime may
> do what we need.
why does it have to be one of the special parameters? Even if you need
it to be somewhat special, there is also SHLChunk::addParameterCallback
that allows you to make your own "special" parameters
> The thing I'm not sure about is how the time value can be updated
> consistently for distributed rendering environments (clusters) as each
> interested shader on each render server/client should use the same time value
> to produce consistent results.
> Looking at the parameter update functions that are actually in the SHLChunk
> class, they seem to receive there current values mostly from current
> RenderAction State. As far as I understand in cluster environments the
> RenderAction will be unique on each host, so assigning a time value on the
> clients RenderAction will be not synced to render servers.
> Asking for local osg system time will return some system specific time that
> is most likely different on each client/server, correct?
yes. Also if you multiple parameters (special or not) they are updated
at different points in time so you'd not get a consistent value for the
system time either (at least not consistent for different shaders).
So the time value should probably be determined once by the application
and then passed to all interested shaders - that's the reason I'm
uncertain if a special parameter is the right way to go here.
> Does anyone have an idea how to distribute the time value correctly to all
> interested SHLChunks?
hmm, the whole distribution problem goes away if you use a regular
parameter on the shader, those are distributed so you can set them on
the client and have all render servers produce the same image.
Cheers,
Carsten
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