More than a year ago, I had worked on the implementation of VK_EXT_sample_locations extension for anv, the IntelVulkan driver of mesa3D, as part of my work for Igalia. The implementation had been reviewed (see acknowledgments) at the time, but as the conformance tests that were available back then had to be improved and that was work in progress, the feature was stalled, and I had forgotten about it… Until some weeks ago, when I realized that it has been merged into mesa! 🎉
As this feature is now available to the users, I’ve decided to write a short blog post to explain what this extension is about. You can read the extension’s specification if you are interested in learning how to use it and other details.
This is the 4th post on OpenGL and Vulkan Interoperability on Linux. The first one was an introduction to EXT_external_objects and EXT_external_objects_fd extensions, the second was describing a simple interoperability use case where a Vulkan allocated textured is filled by OpenGL, and the third was about a slightly more complex use case where a Vulkan texture was filled by Vulkan and displayed by OpenGL. In this 4th and last post about shared textures, we are going to see a use case where a Vulkan texture is filled by Vulkan, then gets overwritten by OpenGL, then is read back from Vulkan and then displayed again using OpenGL. This more complex use case has also been written for Piglit using the small Vulkan framework I’ve written to test the external objects extensions. The source code can be found inside the tests/spec/ext_external_objects directory of the mesa/piglit master branch.
We are going to see a slightly more complex case of Vulkan/GL interoperability where an image is allocated and filled using Vulkan and then it is displayed using OpenGL. This case is implemented in Piglit’svk-image-display test for a 2D RGBA texture (which is one of the most commonly used texture types).
Remember that the code for the test and the Vulkan helper/framework functions as well as the interoperability functions is in tests/spec/ext_external_objects/ Piglit directory.
We are going to see a very simple case of Vulkan/GL interoperability where an image is allocated using Vulkan and filled using OpenGL. This case is implemented in Piglit’s vk-image-overwrite test for images of different formats.
As there were no conformance tests (CTS) for this extension, and we needed to test it, we have written (and we are still writing) small tests for piglit that allow the exchange and the synchronization of the exchange of resources such as buffers, textures, and depth or stencil buffers.
The video mostly shows the behavior of some GL calls and operations with and without the patches that improve the emulation of the ETC/EAC formats on Gen7 GPUs. The same programs run first with the previous ETC/EAC emulation (upper terminal) and then with the new one (lower terminal).