Render Targets

A render target is a surface where rendering operations output their results. In DirectX, render targets are typically associated with textures, allowing you to render scenes not just to the screen, but also to textures that can be used for effects like post-processing, reflections, or off-screen rendering.

Understanding Render Targets

When you perform rendering in DirectX, the output of the pixel shader is written to a specific resource called a render target. This resource is typically a 2D texture that holds the color information for each pixel. By default, the primary render target is the back buffer of the swap chain, which is ultimately displayed on the screen.

Key Concepts

  • Texture2D: The underlying resource used for render targets.
  • Unordered Access View (UAV): While not strictly a render target, UAVs can also be written to, offering more flexibility for certain computational tasks. Render targets are often bound as Output Merger (OM) targets.
  • Viewport: Defines the rectangular region of the render target to which rendering is clipped.
  • RenderTargetView (RTV): A view that binds a texture resource to the output merger stage of the pipeline as a render target.

Creating and Using Render Targets

To use a texture as a render target, you need to:

  1. Create a 2D texture resource with appropriate usage flags (e.g., D3D11_USAGE_DEFAULT) and bind flags (e.g., D3D11_BIND_RENDER_TARGET).
  2. Create a RenderTargetView for this texture.
  3. Bind the RenderTargetView to the output merger stage of the DirectX pipeline using ID3D11DeviceContext::OMSetRenderTargets.

Once bound, all subsequent drawing operations will write to this render target texture instead of the default back buffer.

Example: Creating a Render Target Texture


// Assume pDevice is a valid ID3D11Device pointer

D3D11_TEXTURE2D_DESC textureDesc = {};
textureDesc.Width = 800;
textureDesc.Height = 600;
textureDesc.MipLevels = 1;
textureDesc.ArraySize = 1;
textureDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
textureDesc.SampleDesc.Count = 1;
textureDesc.SampleDesc.Quality = 0;
textureDesc.Usage = D3D11_USAGE_DEFAULT;
textureDesc.BindFlags = D3D11_BIND_RENDER_TARGET | D3D11_BIND_SHADER_RESOURCE; // Bind as RT and SR for post-processing
textureDesc.CPUAccessFlags = 0;
textureDesc.MiscFlags = 0;

ID3D11Texture2D* pRenderTexture = nullptr;
HRESULT hr = pDevice->CreateTexture2D(&textureDesc, nullptr, &pRenderTexture);

if (SUCCEEDED(hr))
{
    D3D11_RENDER_TARGET_VIEW_DESC rtvDesc = {};
    rtvDesc.Format = textureDesc.Format;
    rtvDesc.ViewDimension = D3D11_RTV_DIMENSION_TEXTURE2D;
    rtvDesc.Texture2D.MipSlice = 0;

    ID3D11RenderTargetView* pRenderTargetView = nullptr;
    hr = pDevice->CreateRenderTargetView(pRenderTexture, &rtvDesc, &pRenderTargetView);

    // Now you can bind pRenderTargetView to the OM stage
    // ...
}

Clearing Render Targets

Before rendering to a render target, it's common practice to clear it to a specific color or value. This ensures that any previous frame's contents are removed.


// Assume pContext is a valid ID3D11DeviceContext pointer
// Assume pRenderTargetView is a valid ID3D11RenderTargetView pointer

FLOAT clearColor[4] = { 0.0f, 0.125f, 0.3f, 1.0f }; // RGBA
pContext->ClearRenderTargetView(pRenderTargetView, clearColor);

Multiple Render Targets (MRT)

DirectX supports rendering to multiple render targets simultaneously. This is particularly useful for techniques like deferred shading, where different shading attributes (like diffuse color, normals, and depth) are rendered into separate textures in a single pass.

To use MRT, you need to:

Binding Multiple Render Targets


// Assume pContext is a valid ID3D11DeviceContext pointer
// Assume pRenderTargets is an array of ID3D11RenderTargetView pointers
// Assume numRenderTargets is the number of render targets

pContext->OMSetRenderTargets(numRenderTargets, pRenderTargets, pDepthStencilView); // pDepthStencilView is optional

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