SpriteBatch

This is a native Direct3D 12 implementation of the SpriteBatch helper from XNA Game Studio 4 (Microsoft.Xna.Framework.Graphics.SpriteBatch), providing the same functionality and API.

Related tutorial: Sprites and textures

Header

#include <SpriteBatch.h>

Initialization

To create the Pipeline State Object (PSO) used internally, the SpriteBatch class needs a state description provided in SpriteBatchPipelineStateDescription. The class also requires a ResourceUploadBatch to handle uploading static resources.

ResourceUploadBatch resourceUpload(device);

resourceUpload.Begin();

RenderTargetState rtState(m_deviceResources->GetBackBufferFormat(),
    m_deviceResources->GetDepthBufferFormat());

SpriteBatchPipelineStateDescription pd(rtState);

spriteBatch = std::make_unique<SpriteBatch>(device, resourceUpload, pd);

// Upload the resources to the GPU.
auto uploadResourcesFinished = resourceUpload.End(m_deviceResources->GetCommandQueue());

// Wait for the upload thread to terminate
uploadResourcesFinished.wait();

For exception safety, it is recommended you make use of the C++ RAII pattern and use a std::unique_ptr or std::shared_ptr

Because of the way that DirectX 12 works, if you need a different combination of state you need to create a distinct instance of SpriteBatch. Each SpriteBatch instance has one PSO.

Drawing

The viewport needs to be set explicitly before drawing:

spriteBatch->SetViewport(viewPort);

And the resource descriptor heap for the sprite textures need to be set (see DescriptorHeap for more information):

ID3D12DescriptorHeap* heaps[] = { resourceDescriptors->Heap() };
commandList->SetDescriptorHeaps(_countof(heaps), heaps);

Then use Draw to submit the work to the command-list:

spriteBatch->Begin(commandList);

spriteBatch->Draw(resourceDescriptors->GetGpuHandle(Descriptors::MySpriteTexture),
                  GetTextureSize(tex),
                  XMFLOAT2(x, y));

spriteBatch->End();

The Draw method has many overloads with parameters controlling:

Specify screen position as XMFLOAT2, XMVECTOR or RECT
Optional source rectangle for drawing just part of a sprite sheet
Tint color
Rotation (in radians)
Origin point (position, scaling and rotation are relative to this)
Scale
SpriteEffects enum (for horizontal or vertical mirroring)
Layer depth (for sorting)

To provide flexibility, setting the proper descriptor heaps to render with via SetDescriptorHeaps is left to the caller. You can create as many heaps as you wish in your application, but remember that you can have only a single texture descriptor heap and a single sampler descriptor heap active at a given time.

Sorting

The second parameter to SpriteBatch::Begin is a SpriteSortMode enum. For most efficient rendering, use SpriteSortMode_Deferred (which batches up sprites, then submits them all to the GPU during the End call), and manually draw everything in texture order. If it is not possible to draw in texture order, the second most efficient approach is to use SpriteSortMode_Texture, which will automatically sort on your behalf.

When drawing scenes with multiple depth layers, SpriteSortMode_BackToFront or SpriteSortMode_FrontToBack will sort by the layerDepth parameter specified to each Draw call.

SpriteSortMode_Immediate disables all batching, submitting a separate Direct3D draw call for each sprite. This is expensive, but convenient in rare cases when you need to set shader constants differently per sprite.

Multiple SpriteBatch instances are lightweight. It is reasonable to create several, Begin them at the same time with different sort modes, submit sprites to different batches in arbitrary orders as you traverse a scene, then End the batches in whatever order you want these groups of sprites to be drawn.

SpriteBatch and SpriteSortMode
SpriteBatch sorting part 2
Return of the SpriteBatch: sorting part 3
SpriteSortMode.Immediate in XNA Game Studio 4.0

Alpha blending

Alpha blending defaults to using premultiplied alpha. To make use of 'straight' alpha textures, provide a blend state when creating the SpriteBatch:

SpriteBatchPipelineStateDescription pd(
    rtState,
    &CommonStates::NonPremultiplied);

spriteBatch = std::make_unique<SpriteBatch>(device, resourceUpload, pd);

SpriteFont is designed to work with premultiplied alpha, so if you need to draw both text and straight-alpha content you should have at least two instances of SpriteBatch. Be sure to End one before starting another one using the same command-list or your sort order will be incorrect. Alternatively, you can use MakeSpriteFont to generate 'straight-alpha' .spritefont files using the /NoPremultiply switch.

Texture sampler

If you do not provide a samplerDescriptor, the default is to use a static sampler set to linear filtering with clamp u/v addressing. If you do provide a samplerDescriptor, be sure to set the heap to the command-list when drawing. CommonStates provides heap sampler descriptors which can be used for this purpose:

auto sampler = states->AnisotropicWrap();

SpriteBatchPipelineStateDescription pd(
     rtState, nullptr, nullptr, nullptr, &sampler);

spriteBatch = std::make_unique<SpriteBatch>(device, resourceUpload, pd);

When drawing with this sprite batch:

ID3D12DescriptorHeap* heaps[] = { resourceDescriptors->Heap(), states->Heap() };
commandList->SetDescriptorHeaps(_countof(heaps), heaps);

spriteBatch->Begin(commandList);

spriteBatch->Draw(resourceDescriptors->GetGpuHandle(Descriptors::MySpriteTexture),
                  GetTextureSize(tex),
                  XMFLOAT2(x, y));

spriteBatch->End();

Custom render states

By default SpriteBatch uses premultiplied alpha blending, no depth buffer, counter clockwise culling, and linear filtering with clamp texture addressing. When creating the SpriteBatch, you can control the PSO settings via SpriteBatchPipelineStateDescription

SpriteBatchPipelineStateDescription(
    const RenderTargetState& renderTarget,
    const D3D12_BLEND_DESC* blend,
    const D3D12_DEPTH_STENCIL_DESC* depthStencil,
    const D3D12_RASTERIZER_DESC* rasterizer,
    const D3D12_GPU_DESCRIPTOR_HANDLE* samplerDescriptor)

Pass nullptr for any parameters that should use their default value.

This means that if you want to draw sprites with more than one state configuration, you need more than one instance of SpriteBatch and must Begin/End each batch independently.

Custom shaders

You can provide your own shaders when creating the SpriteBatch by overridding defaults for SpriteBatchPipelineStateDescription.customRootSignature, customVertexShader, and customPixelShader. Your custom root signature should have the following entries at root parameter index 0 & 1 which are bound by SpriteBatch.

DescriptorTable ( SRV(t0), visibility = SHADER_VISIBILITY_PIXEL ),
CBV(b0)

The format of the constant buffer at b0 is as follows:

cbuffer Parameters : register(b0)
{
    row_major float4x4 MatrixTransform;
};

To write a custom sprite batch shader in HLSL, make sure it makes the following signature:

void SpriteVertexShader(inout float4 color    : COLOR0,
                        inout float2 texCoord : TEXCOORD0,
                        inout float4 position : SV_Position)
{
    // TODO
}


float4 SpritePixelShader(float4 color    : COLOR0,
                         float2 texCoord : TEXCOORD0) : SV_Target0
{
    // TODO
}

Custom transform

SpriteBatch::Begin also has a transformMatrix parameter, which can be used for global transforms such as scaling or translation of an entire scene. It otherwise defaults to matrix identity.

XMMATRIX matrix = ...;
spriteBatch->Begin(commandList, SpriteSortMode_Deferred, matrix );

The full transformation depends on the orientation setting and/or the viewport setting for the device. The viewport is obtained from the SpriteBatch::SetViewport method, and then used to construct a view matrix based on the setting provided by theSpriteBatch::SetRotation method.

// DXGI_MODE_ROTATION_ROTATE90
finalMatrix =
    matrix * XMMATRIX(0, -yScale, 0, 0, -xScale, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1);

// DXGI_MODE_ROTATION_ROTATE270
finalMatrix =
    matrix * XMMATRIX(0, yScale, 0, 0, xScale, 0, 0, 0, 0, 0, 1, 0, -1, -1, 0, 1);

//DXGI_MODE_ROTATION_ROTATE180
finalMatrix =
    matrix * XMMATRIX(-xScale, 0, 0, 0, 0, yScale, 0, 0, 0, 0, 1, 0, 1, -1, 0, 1);

// DXGI_MODE_ROTATION_IDENTITY (the default)
finalMatrix =
    matrix * XMMATRIX(xScale, 0, 0, 0, 0, -yScale, 0, 0, 0, 0, 1, 0, -1, 1, 0, 1);

// DXGI_MODE_ROTATION_UNSPECIFIED
finalMatrix = matrix;

Orientation

For phones, laptops, and tablets the orientation of the display can be changed by the user. For Windows Store apps, DirectX applications are encouraged to handle the rotation internally rather than relying on DXGI's auto-rotation handling.

Using the DirectX starting template for Universal Windows Platform (UWP) apps, you will want to add to your CreateWindowSizeDependentResources method:

spriteBatch->SetRotation( m_deviceResources->ComputeDisplayRotation() );

In Common\DeviceResources.h with the standard DirectX UWP template, you need to make ComputeDisplayRotation a public function instead of being private.

When using the directx-vs-templates DeviceResources for UWP, use:

spriteBatch->SetRotation( m_deviceResources->GetRotation() );

Threading model

Creation is fully asynchronous, so you can instantiate multiple SpriteBatch instances at the same time on different threads. Each SpriteBatch instance only supports drawing from one thread at a time, but you can simultaneously submit sprites on multiple threads if you create a separate SpriteBatch instance per command-list.

Work Submission in Direct3D 12

State management

SpriteBatch set it's own root signature and Pipeline State Object (PSO).

The SpriteBatch class assumes you've already set the Render Target view, Depth Stencil view, Viewport, ScissorRects, and Descriptor Heaps (for textures and/or custom samplers), to the command-list provided to Begin.

It is critical that you explicitly call SetViewport to provide the viewport as it cannot be 'read' from the Direct3D 12 command list.