Vulkan ====== Skia has a Vulkan implementation of its GPU backend. The Vulkan backend can be built alongside the OpenGL backend. The client can select between the OpenGL and Vulkan implementation at runtime. The Vulkan backend has reached feature parity with the OpenGL backend. At this time we find that many Vulkan drivers have bugs that Skia triggers for which we have no workaround. We are reporting bugs to vendors as we find them. Windows and Linux ----------------- To build the Vulkan backend, set `skia_use_vulkan=true` in `args.gn`. Android ------- The Vulkan backend can run on any device with Vulkan drivers, including all Android N+ devices. To build the Vulkan backend, set `ndk_api = 24` in `args.gn` to target Android N. Using the Vulkan Backend ------------------------ To 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: sk_sp vkContext = new GrVkBackendContext; vkBackendContext.fInstance = vkInstance; vkBackendContext.fPhysicalDevice = vkPhysDevice; ... vkBackendContext.fInterface.reset(GrVkCreateInterface(instance, vkPhysDevice, extensionFlags); ... sk_sp context = GrContext::MakeVulkan(vkBackendContext); When using the Vulkan backend, GrVkImageInfo is used to construct GrBackendTexture and GrBackendRenderTarget objects that in turn are used to create SkSurface and SkImage objects that refer to VkImages created by the Skia client. The GrBackendObject returned by SkImage::getTextureHandle(), SkSurface::getTextureHandle(), and SkSurface::getRenderTargetHandle() should be interpreted as a GrVkImageInfo*. This allows a client to get the backing VkImage of a SkImage or SkSurface. GrVkImageInfo specifies a VkImage and associated state (tiling, layout, format, etc). After getting a GrVkImageInfo* via getTextureHandle() or getRenderTargetHandle(), the client should check the fImageLayout field to know what layout Skia left the VkImage in before using the VkImage. If the client changes the layout of the VkImage, GrVkImageInfo::updateImageLayout(VkImageLayout layout) should be called before resuming Skia rendering. The client is responsible for any synchronization or barriers needed before Skia performs I/O on a VkImage imported into Skia via GrVkImageInfo. Skia will assume it can start issuing commands referencing the VkImage without the need for additional synchronization.