Posted by Shannon Woods, Technical Program Manager
Today we're pleased to bring you a preview of Android development tools for Vulkan™. Vulkan is a new 3D rendering API which we’ve helped to develop as a member of Khronos, geared at providing explicit, low-overhead GPU (Graphics Processor Unit) control to developers. Vulkan’s reduction of CPU overhead allows some synthetic benchmarks to see as much as 10 times the draw call throughput on a single core as compared to OpenGL ES. Combined with a threading-friendly API design which allows multiple cores to be used in parallel with high efficiency, this offers a significant boost in performance for draw-call heavy applications.
Vulkan support is available now via the Android N Preview on devices which support it, including Nexus 5X and Nexus 6P. (Of course, you will still be able to use OpenGL ES as well!)
You can see Vulkan in action running on an Android device with Robert Hodgin’s Fish Tornado demo, ported by Google’s Art, Copy, and Code team:
Optimization: The Vulkan API
There are many similarities between OpenGL ES and Vulkan, but Vulkan offers new features for developers who need to make every millisecond count.
- Application control of memory allocation. Vulkan provides mechanisms for fine-grained control of how and when memory is allocated on the GPU. This allows developers to use their own allocation and recycling policies to fit their application, ultimately reducing execution and memory overhead and allowing applications to control when expensive allocations occur.
- Asynchronous command generation. In OpenGL ES, draw calls are issued to the GPU as soon as the application calls them. In Vulkan, the application instead submits draw calls to command buffers, which allows the work of forming and recording the draw call to be separated from the act of issuing it to the GPU. By spreading command generation across several threads, applications can more effectively make use of multiple CPU cores. These command buffers can also be reused, reducing the overhead involved in command creation and issuance.
- No hidden work. One OpenGL ES pitfall is that some commands may trigger work at points which are not explicitly spelled out in the API specification or made obvious to the developer. Vulkan makes performance more predictable and consistent by specifying which commands will explicitly trigger work and which will not.
- Multithreaded design, from the ground up. All OpenGL ES applications must issue commands for a context only from a single thread in order to render predictably and correctly. By contrast, Vulkan doesn’t have this requirement, allowing applications to do work like command buffer generation in parallel— but at the same time, it doesn’t make implicit guarantees about the safety of modifying and reading data from multiple threads at the same time. The power and responsibility of managing thread synchronization is in the hands of the application.
- Mobile-friendly features. Vulkan includes features particularly helpful for achieving high performance on tiling GPUs, used by many mobile devices. Applications can provide information about the interaction between separate rendering passes, allowing tiling GPUs to make effective use of limited memory bandwidth, and avoid performing off-chip reads.
- Offline shader compilation. Vulkan mandates support for SPIR-V, an intermediate language for shaders. This allows developers to compile shaders ahead of time, and ship SPIR-V binaries with their applications. These binaries are simpler to parse than high-level languages like GLSL, which means less variance in how drivers perform this parsing. SPIR-V also opens the door for third parties to provide compilers for specialized or cross-platform shading languages.
- Optional validation. OpenGL ES validates every command you call, checking that arguments are within expected ranges, and objects are in the correct state to be operated upon. Vulkan doesn’t perform any of this validation itself. Instead, developers can use optional debug tools to ensure their calls are correct, incurring no run-time overhead in the final product.
Debugging: Validation Layers
As noted above, Vulkan’s lack of implicit validation requires developers to make use of tools outside the API in order to validate their code. Vulkan’s layer mechanism allows validation code and other developer tools to inspect every API call during development, without incurring any overhead in the shipping version. Our guides show you how to build the validation layers for use with the Android NDK, giving you the tools necessary to build bug-free Vulkan code from start to finish.
Develop: Shader toolchain
The Shaderc collection of tools provides developers with build-time and run-time tools for compiling GLSL into SPIR-V. Shaders can be compiled at build time using glslc, a command-line compiler, for easy integration into existing build systems. Or, for shaders which are generated or edited during execution, developers can use the Shaderc library to compile GLSL shaders to SPIR-V via a C interface. Both tools are built on top of Khronos’s reference compiler.
The Vulkan ecosystem is a broad one, and the resources to get you started don’t end here. There is a wealth of material to explore, including:
- Khronos’s Vulkan resources, including overviews, reference pages, specification, and community demos
- Android’s documentation for Vulkan
- Android Vulkan samples
- Android Vulkan tutorials
- LunarG’s LunarXchange has resources for Windows and Linux Vulkan development