To do anything rendering related with Impeller, you need a context. More...

#include <context.h>

Inheritance diagram for impeller::Context:

Public Types
enum class	BackendType { kMetal , kOpenGLES , kVulkan }

Public Member Functions
virtual	~Context ()
	Destroys an Impeller context. More...

virtual BackendType	GetBackendType () const =0
	Get the graphics backend of an Impeller context. More...

virtual std::string	DescribeGpuModel () const =0

virtual bool	IsValid () const =0
	Determines if a context is valid. If the caller ever receives an invalid context, they must discard it and construct a new context. There is no recovery mechanism to repair a bad context. More...

virtual const std::shared_ptr< const Capabilities > &	GetCapabilities () const =0
	Get the capabilities of Impeller context. All optionally supported feature of the platform, client-rendering API, and device can be queried using the `Capabilities`. More...

virtual bool	UpdateOffscreenLayerPixelFormat (PixelFormat format)

virtual std::shared_ptr< Allocator >	GetResourceAllocator () const =0
	Returns the allocator used to create textures and buffers on the device. More...

virtual std::shared_ptr< ShaderLibrary >	GetShaderLibrary () const =0
	Returns the library of shaders used to specify the programmable stages of a pipeline. More...

virtual std::shared_ptr< SamplerLibrary >	GetSamplerLibrary () const =0
	Returns the library of combined image samplers used in shaders. More...

virtual std::shared_ptr< PipelineLibrary >	GetPipelineLibrary () const =0
	Returns the library of pipelines used by render or compute commands. More...

virtual std::shared_ptr< CommandBuffer >	CreateCommandBuffer () const =0
	Create a new command buffer. Command buffers can be used to encode graphics, blit, or compute commands to be submitted to the device. More...

virtual std::shared_ptr< CommandQueue >	GetCommandQueue () const =0
	Return the graphics queue for submitting command buffers. More...

virtual void	Shutdown ()=0
	Force all pending asynchronous work to finish. This is achieved by deleting all owned concurrent message loops. More...

virtual void	StoreTaskForGPU (const fml::closure &task, const fml::closure &failure)

virtual void	InitializeCommonlyUsedShadersIfNeeded () const

virtual void	DisposeThreadLocalCachedResources ()

virtual bool	EnqueueCommandBuffer (std::shared_ptr< CommandBuffer > command_buffer)
	Enqueue command_buffer for submission by the end of the frame. More...

virtual bool	FlushCommandBuffers ()
	Flush all pending command buffers. More...

virtual bool	AddTrackingFence (const std::shared_ptr< Texture > &texture) const

virtual std::shared_ptr< const IdleWaiter >	GetIdleWaiter () const

virtual void	ResetThreadLocalState () const

virtual RuntimeStageBackend	GetRuntimeStageBackend () const =0
	Retrieve the runtime stage for this context type. More...

virtual bool	SubmitOnscreen (std::shared_ptr< CommandBuffer > cmd_buffer)
	Submit the command buffer that renders to the onscreen surface. More...

const Flags &	GetFlags () const

Static Public Attributes
static constexpr int32_t	kMaxTasksAwaitingGPU = 1024

Protected Member Functions
	Context (const Flags &flags)

Protected Attributes
Flags	flags_

std::vector< std::function< void()> >	per_frame_task_

Detailed Description

To do anything rendering related with Impeller, you need a context.

Contexts are expensive to construct and typically you only need one in the process. The context represents a connection to a graphics or compute accelerator on the device.

If there are multiple context in a process, it would typically be for separation of concerns (say, use with multiple engines in Flutter), talking to multiple accelerators, or talking to the same accelerator using different client APIs (Metal, Vulkan, OpenGL ES, etc..).

Contexts are thread-safe. They may be created, used, and collected (though not from a thread used by an internal pool) on any thread. They may also be accessed simultaneously from multiple threads.

Contexts are abstract and a concrete instance must be created using one of the subclasses of Context in //impeller/renderer/backend.

Definition at line 65 of file context.h.

Member Enumeration Documentation

◆ BackendType

enum impeller::Context::BackendType

strong

Enumerator
kMetal
kOpenGLES
kVulkan

Definition at line 67 of file context.h.

                          {
     kMetal,
     kOpenGLES,
     kVulkan,
   };

Constructor & Destructor Documentation

◆ ~Context()

impeller::Context::~Context ( )

virtualdefault

Destroys an Impeller context.

◆ Context()

impeller::Context::Context ( const Flags & flags )

explicitprotected

Definition at line 27 of file context.cc.

27 : flags_(flags) {}

impeller::Context::flags_

Flags flags_

Definition: context.h:272

Member Function Documentation

◆ AddTrackingFence()

bool impeller::Context::AddTrackingFence ( const std::shared_ptr< Texture > & texture ) const

virtual

Definition at line 50 of file context.cc.

                                                                           {
   return false;
 }

◆ CreateCommandBuffer()

virtual std::shared_ptr<CommandBuffer> impeller::Context::CreateCommandBuffer ( ) const

pure virtual

Create a new command buffer. Command buffers can be used to encode graphics, blit, or compute commands to be submitted to the device.

A command buffer can only be used on a single thread. Multi-threaded render, blit, or compute passes must create a new command buffer on each thread.

Returns: A new command buffer.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::TypographerContextSkia::CreateGlyphAtlas(), and impeller::testing::CreateTestYUVTextures().

◆ DescribeGpuModel()

virtual std::string impeller::Context::DescribeGpuModel ( ) const

pure virtual

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

◆ DisposeThreadLocalCachedResources()

virtual void impeller::Context::DisposeThreadLocalCachedResources ( )

inlinevirtual

Dispose resources that are cached on behalf of the current thread.

Some backends such as Vulkan may cache resources that can be reused while executing a rendering operation. This API can be called after the operation completes in order to clear the cache.

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 223 of file context.h.

223 {}

◆ EnqueueCommandBuffer()

bool impeller::Context::EnqueueCommandBuffer ( std::shared_ptr< CommandBuffer > command_buffer )

virtual

Enqueue command_buffer for submission by the end of the frame.

Certain backends may immediately flush the command buffer if batch submission is not supported. This functionality is not thread safe and should only be used via the ContentContext for rendering a 2D workload.

Returns true if submission has succeeded. If the buffer is enqueued then no error may be returned until FlushCommandBuffers is called.

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 33 of file context.cc.

                                                  {
   return GetCommandQueue()->Submit({std::move(command_buffer)}).ok();
 }

References GetCommandQueue().

Referenced by impeller::TypographerContextSkia::CreateGlyphAtlas(), and SubmitOnscreen().

◆ FlushCommandBuffers()

bool impeller::Context::FlushCommandBuffers ( )

virtual

Flush all pending command buffers.

Returns whether or not submission was successful. This functionality is not threadsafe and should only be used via the ContentContext for rendering a 2D workload.

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 38 of file context.cc.

                                   {
   return true;
 }

◆ GetBackendType()

virtual BackendType impeller::Context::GetBackendType ( ) const

pure virtual

Get the graphics backend of an Impeller context.

        This is useful for cases where a renderer needs to track and
        lookup backend-specific resources, like shaders or uniform
        layout information.

        It's not recommended to use this as a substitute for
        per-backend capability checking. Instead, check for specific
        capabilities via `GetCapabilities()`.

Returns: The graphics backend of the Context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, impeller::ContextMTL, and impeller::ContextGLES.

Referenced by impeller::TypographerContextSkia::CreateGlyphAtlas().

◆ GetCapabilities()

virtual const std::shared_ptr<const Capabilities>& impeller::Context::GetCapabilities ( ) const

pure virtual

Get the capabilities of Impeller context. All optionally supported feature of the platform, client-rendering API, and device can be queried using the Capabilities.

Returns: The capabilities. Can never be nullptr for a valid context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::CreateDefaultPipeline(), impeller::TypographerContextSkia::CreateGlyphAtlas(), impeller::RenderTargetAllocator::CreateOffscreen(), impeller::RenderTargetAllocator::CreateOffscreenMSAA(), impeller::PipelineBuilder< VertexShader_, FragmentShader_ >::InitializePipelineDescriptorDefaults(), and impeller::RenderTarget::SetupDepthStencilAttachments().

◆ GetCommandQueue()

virtual std::shared_ptr<CommandQueue> impeller::Context::GetCommandQueue ( ) const

pure virtual

Return the graphics queue for submitting command buffers.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::testing::CreateTestYUVTextures(), and EnqueueCommandBuffer().

◆ GetFlags()

const Flags& impeller::Context::GetFlags ( ) const

inline

Definition at line 267 of file context.h.

267 { return flags_; }

References flags_.

◆ GetIdleWaiter()

std::shared_ptr< const IdleWaiter > impeller::Context::GetIdleWaiter ( ) const

virtual

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 42 of file context.cc.

                                                              {
   return nullptr;
 }

◆ GetPipelineLibrary()

virtual std::shared_ptr<PipelineLibrary> impeller::Context::GetPipelineLibrary ( ) const

pure virtual

Returns the library of pipelines used by render or compute commands.

Returns: The pipeline library. Can never be nullptr for a valid context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::CreatePipelineFuture().

◆ GetResourceAllocator()

virtual std::shared_ptr<Allocator> impeller::Context::GetResourceAllocator ( ) const

pure virtual

Returns the allocator used to create textures and buffers on the device.

Returns: The resource allocator. Can never be nullptr for a valid context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::TypographerContextSkia::CreateGlyphAtlas(), and impeller::testing::CreateTestYUVTextures().

◆ GetRuntimeStageBackend()

virtual RuntimeStageBackend impeller::Context::GetRuntimeStageBackend ( ) const

pure virtual

Retrieve the runtime stage for this context type.

This is used by the engine shell and other subsystems for loading the correct shader types.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

◆ GetSamplerLibrary()

virtual std::shared_ptr<SamplerLibrary> impeller::Context::GetSamplerLibrary ( ) const

pure virtual

Returns the library of combined image samplers used in shaders.

Returns: The sampler library. Can never be nullptr for a valid context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

◆ GetShaderLibrary()

virtual std::shared_ptr<ShaderLibrary> impeller::Context::GetShaderLibrary ( ) const

pure virtual

Returns the library of shaders used to specify the programmable stages of a pipeline.

Returns: The shader library. Can never be nullptr for a valid context.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::ComputePipelineBuilder< ComputeShader_ >::InitializePipelineDescriptorDefaults(), and impeller::PipelineBuilder< VertexShader_, FragmentShader_ >::InitializePipelineDescriptorDefaults().

◆ InitializeCommonlyUsedShadersIfNeeded()

virtual void impeller::Context::InitializeCommonlyUsedShadersIfNeeded ( ) const

inlinevirtual

Run backend specific additional setup and create common shader variants.

This bootstrap is intended to improve the performance of several first frame benchmarks that are tracked in the flutter device lab. The workload includes initializing commonly used but not default shader variants, as well as forcing driver initialization.

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 216 of file context.h.

216 {}

◆ IsValid()

virtual bool impeller::Context::IsValid ( ) const

pure virtual

Determines if a context is valid. If the caller ever receives an invalid context, they must discard it and construct a new context. There is no recovery mechanism to repair a bad context.

It is convention in Impeller to never return an invalid context from a call that returns an pointer to a context. The call implementation performs validity checks itself and return a null context instead of a pointer to an invalid context.

How a context goes invalid is backend specific. It could happen due to device loss, or any other unrecoverable error.

Returns: If the context is valid.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

Referenced by impeller::CreatePipelineFuture().

◆ ResetThreadLocalState()

void impeller::Context::ResetThreadLocalState ( ) const

virtual

Resets any thread local state that may interfere with embedders.

Today, only the OpenGL backend can trample on thread local state that the embedder can access. This call puts the GL state in a sane "clean" state.

Impeller itself is resilient to a dirty thread local state table.

Definition at line 46 of file context.cc.

                                           {
   // Nothing to do.
 }

◆ Shutdown()

virtual void impeller::Context::Shutdown ( )

pure virtual

Force all pending asynchronous work to finish. This is achieved by deleting all owned concurrent message loops.

Implemented in impeller::SurfaceContextVK, impeller::ContextVK, and impeller::ContextMTL.

◆ StoreTaskForGPU()

virtual void impeller::Context::StoreTaskForGPU	(	const fml::closure &	task,
		const fml::closure &	failure
	)

inlinevirtual

Stores a task on the ContextMTL that is awaiting access for the GPU.

The task will be executed in the event that the GPU access has changed to being available or that the task has been canceled. The task should operate with the SyncSwitch to make sure the GPU is accessible.

If the queue of pending tasks is cleared without GPU access, then the failure callback will be invoked and the primary task function will not

Threadsafe.

task will be executed on the platform thread.

Reimplemented in impeller::ContextMTL.

Definition at line 205 of file context.h.

                                                           {
     FML_CHECK(false && "not supported in this context");
   }

◆ SubmitOnscreen()

bool impeller::Context::SubmitOnscreen ( std::shared_ptr< CommandBuffer > cmd_buffer )

virtual

Submit the command buffer that renders to the onscreen surface.

Reimplemented in impeller::SurfaceContextVK, and impeller::ContextVK.

Definition at line 54 of file context.cc.

                                                                     {
   return EnqueueCommandBuffer(std::move(cmd_buffer));
 }

References EnqueueCommandBuffer().

◆ UpdateOffscreenLayerPixelFormat()

bool impeller::Context::UpdateOffscreenLayerPixelFormat ( PixelFormat format )

virtual

Reimplemented in impeller::ContextMTL.

Definition at line 29 of file context.cc.

                                                                 {
   return false;
 }

Member Data Documentation

◆ flags_

Flags impeller::Context::flags_

protected

Definition at line 272 of file context.h.

Referenced by GetFlags().

◆ kMaxTasksAwaitingGPU

constexpr int32_t impeller::Context::kMaxTasksAwaitingGPU = 1024

staticconstexpr

The maximum number of tasks that should ever be stored for StoreTaskForGPU.

This number was arbitrarily chosen. The idea is that this is a somewhat rare situation where tasks happen to get executed in that tiny amount of time while an app is being backgrounded but still executing.

Definition at line 79 of file context.h.

◆ per_frame_task_

std::vector<std::function<void()> > impeller::Context::per_frame_task_

protected

Definition at line 273 of file context.h.

The documentation for this class was generated from the following files:

impeller/renderer/context.h
impeller/renderer/context.cc

Public Types

Public Member Functions

Static Public Attributes

Protected Member Functions

Protected Attributes

Detailed Description

Member Enumeration Documentation

◆ BackendType

Constructor & Destructor Documentation

◆ ~Context()

◆ Context()

Member Function Documentation

◆ AddTrackingFence()

◆ CreateCommandBuffer()

◆ DescribeGpuModel()

◆ DisposeThreadLocalCachedResources()

◆ EnqueueCommandBuffer()

◆ FlushCommandBuffers()

◆ GetBackendType()

◆ GetCapabilities()

◆ GetCommandQueue()

◆ GetFlags()

◆ GetIdleWaiter()

◆ GetPipelineLibrary()

◆ GetResourceAllocator()

◆ GetRuntimeStageBackend()

◆ GetSamplerLibrary()

◆ GetShaderLibrary()

◆ InitializeCommonlyUsedShadersIfNeeded()

◆ IsValid()

◆ ResetThreadLocalState()

◆ Shutdown()

◆ StoreTaskForGPU()

◆ SubmitOnscreen()

◆ UpdateOffscreenLayerPixelFormat()

Member Data Documentation

◆ flags_

◆ kMaxTasksAwaitingGPU

◆ per_frame_task_