1Vulkan 2====== 3 4Skia has a Vulkan implementation of its GPU backend. The Vulkan backend can be 5built alongside the OpenGL backend. The client can select between the OpenGL 6and Vulkan implementation at runtime. The Vulkan backend has reached feature 7parity with the OpenGL backend. At this time we find that many Vulkan drivers 8have bugs that Skia triggers for which we have no workaround. We are reporting 9bugs to vendors as we find them. 10 11Windows and Linux 12----------------- 13To build the Vulkan backend, set `skia_vulkan_sdk` to the path to your Vulkan SDK in `args.gn`. 14This defaults to the environment variable `VULKAN_SDK`. 15 16Android 17------- 18The Vulkan backend can run on any device with Vulkan drivers, including all Android N+ devices. 19To build the Vulkan backend, set `ndk_api = 24` in `args.gn` to target Android N. 20 21Using the Vulkan Backend 22------------------------ 23 24To create a GrContext that is backed by Vulkan the client creates a Vulkan device and queue, initializes a GrVkBackendContext to describe the context, and then calls GrContext::MakeVulkan: 25 26<!--?prettify lang=c++?--> 27 sk_sp<GrVkBackendContext> vkContext = new GrVkBackendContext; 28 vkBackendContext.fInstance = vkInstance; 29 vkBackendContext.fPhysicalDevice = vkPhysDevice; 30 ... 31 vkBackendContext.fInterface.reset(GrVkCreateInterface(instance, vkPhysDevice, extensionFlags); 32 ... 33 34 sk_sp<GrContext> context = GrContext::MakeVulkan(vkBackendContext); 35 36When using the Vulkan backend, GrVkImageInfo is used to construct GrBackendTexture 37and GrBackendRenderTarget objects that in turn are used to create SkSurface and SkImage 38objects that refer to VkImages created by the Skia client. 39 40The GrBackendObject returned by SkImage::getTextureHandle(), 41SkSurface::getTextureHandle(), and SkSurface::getRenderTargetHandle() should be 42interpreted as a GrVkImageInfo*. This allows a client to get the backing VkImage 43of a SkImage or SkSurface. 44 45GrVkImageInfo specifies a VkImage and associated state (tiling, layout, format, etc). 46After getting a GrVkImageInfo* via getTextureHandle() or 47getRenderTargetHandle(), the client should check the fImageLayout field to know 48what layout Skia left the VkImage in before using the VkImage. If the client 49changes the layout of the VkImage, 50GrVkImageInfo::updateImageLayout(VkImageLayout layout) should be called before 51resuming Skia rendering. 52 53The client is responsible for any synchronization or barriers needed before 54Skia performs I/O on a VkImage imported into Skia via GrVkImageInfo. Skia will 55assume it can start issuing commands referencing the VkImage without the need 56for additional synchronization. 57