OpenGL Texture via GstGLUpload - So close! - Proper Post

[Lasse Laursen]

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\"";

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 );

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!

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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