ID3D11Device and ID3D11DeviceContext

The Direct3D 11 API utilizes two primary interfaces for managing graphics operations: ID3D11Device and ID3D11DeviceContext. These interfaces work together to enable efficient interaction with the graphics hardware.

ID3D11Device

The ID3D11Device interface represents the graphics adapter. It is used to create Direct3D objects such as textures, buffers, shaders, and state objects. Think of the device as the factory where all your graphics resources are manufactured.

Key Responsibilities:

• Resource Creation: Creating all Direct3D objects (e.g., ID3D11Buffer, ID3D11Texture2D, ID3D11ShaderResourceView).
• Device Capabilities: Querying information about the graphics hardware and its capabilities.
• State Objects: Creating various state objects like blend states, depth-stencil states, rasterizer states, and sampler states.

You typically obtain an ID3D11Device by calling D3D11CreateDevice or D3D11CreateDeviceAndSwapChain.

Example of Device Creation:

ID3D11Device* pDevice = nullptr;
ID3D11DeviceContext* pDeviceContext = nullptr;
D3D_FEATURE_LEVEL featureLevel;

HRESULT hr = D3D11CreateDevice(
    nullptr,                    // pAdapter
    D3D_DRIVER_TYPE_HARDWARE,   // DriverType
    nullptr,                    // Software
    0,                          // Flags
    nullptr,                    // pFeatureLevels
    0,                          // FeatureLevels
    D3D11_SDK_VERSION,          // SDKVersion
    &pDevice,                   // ppDevice
    &featureLevel,              // pFeatureLevel
    &pDeviceContext             // ppImmediateContext
);

if (FAILED(hr)) {
    // Handle error
}
            

ID3D11DeviceContext

The ID3D11DeviceContext interface represents a command buffer that is used to set rendering states and issue drawing commands. It's where the actual "drawing" happens. Direct3D 11 distinguishes between an immediate context and deferred contexts.

Immediate Context

The immediate context is accessed directly from the ID3D11Device. It executes commands as soon as they are issued. This is typically used for most rendering operations in a single-threaded application.

Deferred Contexts

Deferred contexts are created from the ID3D11Device. They record rendering commands into a command buffer that can be replayed later or on a different thread. This is useful for multithreaded rendering scenarios, allowing one thread to record commands while another thread executes them.

Key Responsibilities:

• Setting State: Configuring the pipeline state (e.g., input assembler, vertex shader, pixel shader, output merger).
• Binding Resources: Associating resources like buffers and textures with pipeline stages.
• Issuing Draw Calls: Submitting drawing commands to the GPU (e.g., Draw, DrawIndexed, Dispatch).
• Executing Command Lists: Replaying commands recorded by deferred contexts.

Example of Binding and Drawing:

// Assume pDeviceContext, pVertexBuffer, pInputLayout, pVertexShader, pPixelShader, pRenderTargetView are valid

// Bind vertex buffer and input layout
UINT stride = sizeof(MyVertex);
UINT offset = 0;
pDeviceContext->IASetVertexBuffers(0, 1, &pVertexBuffer, &stride, &offset);
pDeviceContext->IASetInputLayout(pInputLayout);

// Bind shaders
pDeviceContext->VSSetShader(pVertexShader, nullptr, 0);
pDeviceContext->PSSetShader(pPixelShader, nullptr, 0);

// Bind render target
pDeviceContext->OMSetRenderTargets(1, &pRenderTargetView, nullptr);

// Set primitive topology
pDeviceContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);

// Draw call
pDeviceContext->Draw(3, 0); // Draw a single triangle