Libva Buffer Sharing HowTo

Beignet has extensions (clCreateBufferFromLibvaIntel/clCreateImageFromLibvaIntel) to share gpu buffer object with libva. So users can utilize OpenCL to do processing on VASurface or VABuffer without buffer copy.

Prerequisite

Libva api version >= 0.36.0. Please check your libva api version by command pkg-config --modversion libva.

Steps

In order to use the extension clCreateBufferFromLibvaIntel/clCreateImageFromLibvaIntel in your program, please follow the steps as below (We have added an example of using clCreateImageFromLibvaIntel, please read next section for details):

• Get the address of this extension by the function: clGetExtensionFunctionAddress("clCreateBufferFromLibvaIntel") or clGetExtensionFunctionAddress("clCreateImageFromLibvaIntel")

• Invoke vaAcquireBufferHandle to get VASurface/VABuffer's handle, which you want to do processing by OpenCL.

• Use clCreateBufferFromLibvaIntel/clCreateImageFromLibvaIntel to create corresponding cl memory object from VASurface/VABuffer's handle. If you create a normal VASurface, you should use clCreateImageFromLibvaIntel to create a cl image object from VASurface, because VASurface is a tiling gpu buffer object. The only case you should use clCreateBufferFromLibvaIntel to create a cl buffer object from VASurface is that: The VASurface is created from an external untiling gpu buffer object. And You should use clCreateBufferFromLibvaIntel to create a cl buffer object from VABuffer.

• Use OpenCL to do post-processing.

• Release this cl buffer object by clReleaseMemObject.

• Unlock this VABuffer by vaReleaseBufferHandle.

Sample code

We have developed an example of using clCreateImageFromLibvaIntel in examples/libva_buffer_sharing directory. This example read a source nv12 file to a VASurface, and create a target VASurface. Then create corresponding cl image objects from them. After using ocl to do a mirror effect post-processing on this source surface, target VASurface is shown on screen by default.

• Add option -DBUILD_EXAMPLES=ON to enable building examples when running cmake, such as:

  > mkdir build

  > cd build

  > cmake -DBUILD_EXAMPLES=ON ../

• Build source code:

  > make

• Run:

  > cd examples

  > . ../utests/setenv.sh

  > ./example-libva_buffer_sharing

In addition, you can choose to save the result as a nv12 file. You can use gst-launch-1.0 to see the result. Just install gstreamer1.0-plugins-base, gstreamer1.0-plugins-bad and gstreamer1.0-x by apt on Ubuntu. Then running the following command:

> gst-launch-1.0 filesrc location=file_name ! videoparse format=nv12 width=xxx height=xxx \ ! imagefreeze ! videoconvert ! video/x-raw, format=BGRx ! ximagesink