| Flutter Impeller |

Public Types | Public Member Functions | Public Attributes | Static Public Attributes | Protected Member Functions | Protected Attributes | List of all members
impeller::Context Class Referenceabstract

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

`#include <context.h>`

Inheritance diagram for impeller::Context:

## Public Types
enum | BackendType { BackendType::kMetal, BackendType::kOpenGLES, BackendType::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 std::function< void()> &task)
virtual void | InitializeCommonlyUsedShadersIfNeeded () const

## Public Attributes
CaptureContext | capture

## Static Public Attributes
static constexpr int32_t | kMaxTasksAwaitingGPU = 10

## Protected Member Functions
| Context ()

## Protected Attributes
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 46 of file context.h.

## Member Enumeration Documentation

## ◆ BackendType

enum impeller::Context::BackendType
| strong

Enumerator
kMetal |
kOpenGLES |
kVulkan |

Definition at line 48 of file context.h.

48 {
49 kMetal,
50 kOpenGLES,
51 kVulkan,
52 };

## Constructor & Destructor Documentation

## ◆ ~Context()

impeller::Context::~Context | ( |  | ) |
| virtual default

Destroys an Impeller context.

## ◆ Context()

impeller::Context::Context | ( |  | ) |
| protected

Definition at line 13 of file context.cc.

13 : capture(CaptureContext::MakeInactive()) {}

## Member Function Documentation

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

## ◆ DescribeGpuModel()

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

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

## ◆ 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::ContextVK, impeller::ContextMTL, impeller::SurfaceContextVK, and impeller::ContextGLES.

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

Referenced by impeller::CreateDefaultPipeline(), impeller::TypographerContextSkia::CreateGlyphAtlas(), impeller::TypographerContextSTB::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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

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

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

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

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

## ◆ InitializeCommonlyUsedShadersIfNeeded()

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

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::ContextVK, and impeller::SurfaceContextVK.

Definition at line 195 of file context.h.

195 {}

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

Referenced by impeller::CreatePipelineFuture().

## ◆ 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::ContextVK, impeller::ContextMTL, and impeller::SurfaceContextVK.

## ◆ StoreTaskForGPU()

virtual void impeller::Context::StoreTaskForGPU | ( | const std::function< void()> & | task | ) |
| inline virtual

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.

Threadsafe.

`task` will be executed on the platform thread.

Reimplemented in impeller::ContextMTL.

Definition at line 185 of file context.h.

185 {
186 FML_CHECK(false && "not supported in this context");
187 }

## ◆ UpdateOffscreenLayerPixelFormat()

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

Reimplemented in impeller::ContextMTL.

Definition at line 15 of file context.cc.

15 {
16 return false;
17 }

## Member Data Documentation

## ◆ capture

CaptureContext impeller::Context::capture

Definition at line 174 of file context.h.

## ◆ kMaxTasksAwaitingGPU

constexpr int32_t impeller::Context::kMaxTasksAwaitingGPU = 10
| static constexpr

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 60 of file context.h.

## ◆ per_frame_task_

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

Definition at line 200 of file context.h.

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

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

impeller::Context::capture
CaptureContext capture
Definition: context.h:174
impeller::compiler::TargetPlatform::kVulkan
@ kVulkan
impeller::CaptureContext::MakeInactive
static CaptureContext MakeInactive()
Definition: capture.cc:155
impeller::compiler::TargetPlatform::kOpenGLES
@ kOpenGLES
impeller::RuntimeStageBackend::kMetal
@ kMetal