[osg-users] FFmpegImageStream thread safety

[OpenSceneGraph Users]

Hi Robert,

Thanks for your response.

If FFmpegImageStream::publishNewFrame is invoked from a separate thread.
Is it then somehow guaranteed that (for example) Texture2D::apply is not
using/reading from the image object, while
FFmpegImageStream::publishNewFrame is modifying it ?

Cheers,

Ben

Op vr 31 jul. 2020 om 21:24 schreef Robert Osfield <robert.osfield at gmail.com
>:

> Hi Ben,
>
> I'm away from my dev computer so just commenting off the top of my.
> FFmpegImageStream should be double buffered so that the ffmpeg thread
> writing to the image will be writing to one part of the data, while the
> other half is available to be read by the graphics thread.  This should
> avoid threading issues.
>
> The threading used by the ffmpeg plugin is separate from the viewer
> threading so settings related to the viewer won't be important, nor will
> general settings of the scene graph.
>
> You should be able to just add the ffmpeg genearted imagestream to a
> texture, start the steam going and then largely forget about it.
>
> Robert.
>
> On Friday, 31 July 2020 at 20:15:45 UTC+1 bjs.me... at gmail.com wrote:
>
>> Hi,
>>
>> I was just looking at FFmpegImageStream, I am not very familiar with this
>> code, but I have some questions.
>>
>> It is not immediately clear to me how FFmpegImageStream::publishNewFrame
>> is thread safe.
>> It seems like the image data is set (setImage) from the video decoder
>> thread.
>> The image then uses a pointer to one of the buffers of the video decoder
>> (of which the contents might also change ?).
>>
>> FFmpegImageStream also doesn't seem to override requiresUpdateCall, which
>> I believe will result in the texture not being dynamic
>> (Texture2D::setImage).
>> Which could be used, for example in StateSet::computeDataVariance(), to
>> determine whether the StateSet should be dynamic (which is needed for
>> multithreaded rendering).
>>
>> If anyone could shed more light on this subject, it would be very much
>> appreciated.
>>
>> Thank you.
>>
>> Cheers,
>>
>> Ben
>>
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