OpenGL Texture via GstGLUpload - So close! - Proper Post

Fri Jan 16 11:42:10 PST 2015

Hey Matthew,

Thanks for the reply and especially the example. I'm working on getting 
it function with the cinder framework. At first it seemed quite odd to 
hand over the context as a result of a bus message, but I can see the 
logic in not needing to create a secondary OpenGL context for gstreamer 
to make textures in, if one already exists. I do have one question though:

Is it vital to turn off the OpenGL context when sharing it with 
Gstreamer? I've done a little context sharing before and I don't recall 
having to actively turn any contexts 'off'.

Regards,
Lasse

On 16-01-2015 00:27, Matthew Waters wrote:
> A couple of points added inline.
>
> On 16/01/15 03:14, Lasse Laursen wrote:
>> Hello!
>>
>> Apologies for the double post, but my inept handling of Thunderbird 
>> caused my last post to be appended to an unrelated thread. Sorry 
>> about that Luis dArquer.
>>
>> For the sake of posterity, here's is the original question:
>>
>> I feel like I am so close to finally getting through to the other 
>> side with this problem, so I'm hoping someone can give me a few clues 
>> as to what pieces of the puzzle are missing. I used to use gStreamer 
>> as a pure 'decoding' library using this simple pipeline:
>>
>> uridecodebin uri=" + mPathToVideoFile +    " ! videoconvert ! appsink 
>> name=sink caps="video/x-raw,format=RGB,pixel-aspect-ratio=1/1";
>>
>> With this pipeline, I could quite easily grab the frames arriving at 
>> the sink and use them however I pleased. Mostly just throwing them on 
>> a texture in OpenGL and displaying them various places. This approach 
>> is - of course - quite horrible. I'm not making use of gstreamer as a 
>> fully-fledged media pipeline. So to rectify that - and because I'd 
>> like to run some simple shaders on the video data - I am now using 
>> this (almost as) simple pipeline:
>>
>> uridecodebin uri=" + mPathToVideoFile + " ! glshader name=shader 
>> location=" + pathToShader + " vars=\"float silver = float( 0.8 ); \" 
>> ! appsink name=sink 
>> caps=\"video/x-raw,format=RGB,pixel-aspect-ratio=1/1\"";
>
> 1. You should set the appsink caps to contain the memory:GstGLMemory 
> caps features. e.g. video/x-raw(memory:GstGLMemory),format=RGBA... see 
> gst-inspect-1.0 glshader for the supported formats and features.  
> Otherwise, glshader (and any GL element) will download the texture 
> upon seeing the system memory caps.
>
>> I make sure to share my current OpenGL context with the glshader 
>> element thusly:
>>
>> mPipeline_ShaderPre = gst_bin_get_by_name( GST_BIN( mGstPipeline ), 
>> "shader" );
>> HGLRC mainContext = ::wglGetCurrentContext();
>> g_object_set( mPipeline_ShaderPre, "other-context", mainContext, NULL );
>
> 2. The "other-context" property expects a GstGLContext rather than a 
> platform specific handle.  You can wrap a context handle using 
> gst_gl_context_new_wrapped().  However, in master there is no 
> "other-context" property anymore so the sharing of GL context happens 
> using GstContext.  See for example 
> http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/tests/examples/gl/sdl/sdlshare.c#n232 
> and the GstContext documentation.
>
>> Not sure if this is correct to be honest, but I didn't see any errors 
>> in gstreamers logs. Anyway - fast forward to my callback function 
>> that fires whenever a sample is ready at the sink I proceed to grab a 
>> Sample, from which I grab a Buffer, from which I grab a Frame, from 
>> which I grab a Texture ID, thusly:
>>
>> GstSample* gstVideoSinkSample = gst_app_sink_pull_sample( 
>> GST_APP_SINK( appsink ) );
>> GstBuffer* gstBuffer = gst_sample_get_buffer( gstVideoSinkSample );
>> if ( !gst_video_frame_map( &gstFrame, &gstInfo, gstBuffer, 
>> static_cast<GstMapFlags>( GST_MAP_READ | ( GST_MAP_FLAG_LAST << 1 ) ) 
>> ) )
>>     {
>>         errorToConsole( true, "Failed to map video frame" );
>>     }
>> GLuint textureId = *(guint *) gstFrame.data[0];
>>
>> The result is the number 6. Which I felt was a plausible Texture ID 
>> handle. But when I then use a lovely tool named imdebug, and presume 
>> that the target for the texture is GL_TEXTURE_2D (which might be 
>> wrong), it throws a fit, because it attempts to determine the width 
>> and height of said texture via these calls:
>>
>> glBindTexture(target, texture);
>>   glGetTexLevelParameteriv(target, 0, GL_TEXTURE_WIDTH, &w);
>>   glGetTexLevelParameteriv(target, 0, GL_TEXTURE_HEIGHT, &h);
>>
>> So clearly something is wrong. Some place along this winding road, 
>> I've misunderstood something or overlooked something. I'd much 
>> appreciate any suggestions/clues!
>>
>> I myself am wondering if a callback at the sink is the right place to 
>> grab the texture ID, but I'm not sure how to get at it any earlier, 
>> and if that's wise. I am also unsure of how long this texture Id is 
>> valid if I want to render it on to a quad. I hope someone can shed a 
>> bit of light!
>
> It will be valid for as long as it's not overwritten/reused by the 
> producing element which generally means while you keep a ref to the 
> buffer or have the video frame mapped.
>
>> Regards,
>> Lasse
>>
>> -- 
>> Lasse Farnung Laursen
>> Researcher at the University of Tokyo
>> www.lasselaursen.com <http://www.lasselaursen.com>
>> Twitter: @PMP_J <https://twitter.com/PMP_J>
>
>
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-- 
Lasse Farnung Laursen
Researcher at the University of Tokyo
www.lasselaursen.com <http://www.lasselaursen.com>
Twitter: @PMP_J <https://twitter.com/PMP_J>
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