Sprites and textures

Getting Started

In this lesson, we will cover the basics of creating a texture from a bitmap file, and then rendering it using a 2D sprite with various drawing options.

Setup

First create a new project using the instructions from the previous lessons: Using DeviceResources and Adding the DirectX Tool Kit which we will use for this lesson.

Background

A sprite is a bitmap rendered at some location on the screen. For Direct3D, this requires making use of:

A 2D texture resource which is a surface containing the bitmap image pixel data.
The shader resource view which describes the properties of the texture resource.

In older versions of Direct3D, the texture resource and shader resource view (SRV) were combined into a single interface. In Direct3D 11, these are distinct objects to allow for different interpretations of the same resource data (such as an array of 2D textures or a cubemap).

A sampler state object which describes how the GPU should handle various aspects of reading the texture data for rendering (such as image filtering and/or tiling of the bitmap).
A blend state object which indicates how the GPU should combine existing information in the render target with the texture data.
Additional Direct3D objects are also required (vertex buffer, index buffer, rasterizer state object, input layout, vertex shader, pixel shader, and constant buffer), but in this tutorial these are handled by SpriteBatch.

Loading a texture

Start by saving cat.png into your new project's directory, and then from the top menu select Project / Add Existing Item.... Select "cat.png" and click "OK".

In the Game.h file, add the following variable to the bottom of the Game class's private declarations:

Microsoft::WRL::ComPtr<ID3D11ShaderResourceView> m_texture;

In Game.cpp, add to the TODO of CreateDeviceDependentResources:

DX::ThrowIfFailed(
    CreateWICTextureFromFile(device, L"cat.png", nullptr,
    m_texture.ReleaseAndGetAddressOf()));

In Game.cpp, add to the TODO of OnDeviceLost:

m_texture.Reset();

Build and run the application which will still not be displaying anything but the cornflower blue window, but will have a texture loaded.

Click here for troubleshooting advice

If you get a runtime exception, then you may have the "cat.png" in the wrong folder, have modified the "Working Directory" in the "Debugging" configuration settings, or otherwise changed the expected paths at runtime of the application. You should set a break-point on CreateWICTextureFromFile and step into the code to find the exact problem.

Drawing a sprite

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

std::unique_ptr<DirectX::SpriteBatch> m_spriteBatch;
DirectX::SimpleMath::Vector2 m_screenPos;
DirectX::SimpleMath::Vector2 m_origin;

For the original load of our sprite, we only need a ID3D11ResourceShaderView object as that's all you require to render. This time, however, we also want to obtain the pixel size of the image which is done by requesting the reader return the ID3D11Resource interface as well as the SRV.

In Game.cpp, modify TODO of CreateDeviceDependentResources to be:

auto context = m_deviceResources->GetD3DDeviceContext();
m_spriteBatch = std::make_unique<SpriteBatch>(context);

ComPtr<ID3D11Resource> resource;
DX::ThrowIfFailed(
    CreateWICTextureFromFile(device, L"cat.png",
    resource.GetAddressOf(),
    m_texture.ReleaseAndGetAddressOf()));

ComPtr<ID3D11Texture2D> cat;
DX::ThrowIfFailed(resource.As(&cat));

CD3D11_TEXTURE2D_DESC catDesc;
cat->GetDesc(&catDesc);

m_origin.x = float(catDesc.Width / 2);
m_origin.y = float(catDesc.Height / 2);

In Game.cpp, add to the TODO of CreateWindowSizeDependentResources:

auto size = m_deviceResources->GetOutputSize();
m_screenPos.x = float(size.right) / 2.f;
m_screenPos.y = float(size.bottom) / 2.f;

If using the UWP template, you also need to add m_spriteBatch->SetRotation(m_deviceResources->GetRotation()); to handle display orientation changes.

If using Xbox One DirectX 11.X "fast semantics", you also need to add m_spriteBatch->SetViewport(m_deviceResources->GetScreenViewport());.

In Game.cpp, add to the TODO of OnDeviceLost:

m_spriteBatch.reset();

In Game.cpp, add to the TODO of Render:

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, 0.f, m_origin);

m_spriteBatch->End();

Build and run, and you should get the following screen:

Screenshot of cat sprite

Alpha mode

One thing you should notice is that the edges of the cat look strange with a bit of white outline. The problem here is that the cat.png file's alpha channel is straight alpha (i.e. the pixels are of the form (R,G,B,A)). The default behavior of SpriteBatch, however, is to assume you are using premultiplied alpha (i.e. the pixels are of the form (R*A, G*A, B*A, A)). There are many reasons why using premultiplied alpha is superior, but for now we can fix this mismatch by changing our use of SpriteBatch to use straight alpha blending instead by supplying our own ID3D11BlendState object. We'll make use of the CommonStates factory to provide one of the built-in blend state objects.

In the Game.h file, add the following variable to the bottom of the Game class's private declarations:

std::unique_ptr<DirectX::CommonStates> m_states;

In Game.cpp, add to the TODO of CreateDeviceDependentResources:

m_states = std::make_unique<CommonStates>(device);

In Game.cpp, add to the TODO of OnDeviceLost:

m_states.reset();

In Game.cpp, modify the TODO of Render:

m_spriteBatch->Begin(SpriteSortMode_Deferred, m_states->NonPremultiplied());

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, 0.f, m_origin);

m_spriteBatch->End();

Build and run again, and you'll get a nice clean cat:

Screenshot of cat sprite

Using DDS files for textures

Rather than use a PNG and the Windows Imaging Component (WIC) to load the texture, a more efficient thing for us to do is to make use of a DDS file instead. A DDS file is a container for all kinds of Direct3D resources including 1D and 2D textures, cubemaps, volume maps, arrays of 1D or 2D textures or cubemaps each optionally with mipmaps. It can contain a wide-array of pixel formats and hardware-supported 'block-compression' schemes to save on video memory usage at runtime.

Visual Studio has a built-in system for converting images to DDS as part of the build process, which you can read about here.

For this tutorial, we will instead make of use of the DirectXTex texconv command-line tool.

Download the Texconv.exe from the DirectXTex site save the EXE into your project's folder.
Open a Command Prompt and then change to your project's folder.

Then run the following command-line:

texconv cat.png -pmalpha -m 1 -f BC3_UNORM

Then from the top menu in Visual Studio select Project / Add Existing Item.... Select cat.dds and click "OK".

Now will return to Game.cpp in the CreateDeviceDependentResources and change our use of CreateWICTextureFromFile to CreateDDSTextureFromFile:

DX::ThrowIfFailed(
    CreateDDSTextureFromFile(device, L"cat.dds",
        resource.GetAddressOf(),
    m_texture.ReleaseAndGetAddressOf()));

Note that since we used the option -pmalpha, we should also make sure we change back to the default Begin in our Render because our "cat.dds" has premultiplied alpha in it.

In Game.cpp, modify the TODO of Render:

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, 0.f, m_origin);

m_spriteBatch->End();

Build and run we are rendering our 'clean' cat with premultiplied alpha:

Screenshot of cat sprite

Technical notes

The switch -pmalpha causes the texconv command-line tool to convert the image to premultiplied alpha before saving the .dds file. This assumes the source image is in straight-alpha.
The switch -m 1 disables the generation of mipmaps for the image. By default, the tool generates a full set of mipmaps when converting to a .dds, but since our source image is not a power of two in width & height, it also generates a warning message about use with feature level 9.x devices. For standard sprites, we typically do not make use of mipmaps.
The switch -f BC3_UNORM selects the DXGI_FORMAT_BC3_UNORM format for the resulting .dds file. In combination with the -pmalpha switch, this results in the "DXT4" block-compression format being used.

Rotating a sprite

Now that we have our cat rendering, we can start to animate it. Here's a simple rotation where we are using the cosf function to give us a time-varying value from -1 to 1.

In Game.cpp, modify the TODO of Render:

float time = float(m_timer.GetTotalSeconds());

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, cosf(time) * 4.f, m_origin);

m_spriteBatch->End();

Build and run to see the cat spinning.

Scaling a sprite

We can scale a sprite's size as well. Again, we are using cosf to give us a time-varying value between -1 and 1.

In Game.cpp, modify the TODO of Render:

float time = float(m_timer.GetTotalSeconds());

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, 0.f, m_origin,
    cosf(time) + 2.f);

m_spriteBatch->End();

Build and run to see the cat growing and shrinking.

Tinting a sprite

We can modify the color of the sprite with a tint as well:

In Game.cpp, modify the TODO of Render:

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::Green, 0.f, m_origin);

m_spriteBatch->End();

Build and run to see a green-tinged cat.

Tiling a sprite

With the optional source-rectangle parameter, we can tile a sprite.

In the Game.h file, add the following variable to the bottom of the Game class's private declarations:

RECT m_tileRect;

In the Game.cpp file, modify in the TODO section of CreateDeviceDependentResources:

change

m_origin.x = float(catDesc.Width / 2);
m_origin.y = float(catDesc.Height / 2);

to

m_origin.x = float(catDesc.Width * 2);
m_origin.y = float(catDesc.Height * 2);

m_tileRect.left = catDesc.Width * 2;
m_tileRect.right = catDesc.Width * 6;
m_tileRect.top = catDesc.Height * 2;
m_tileRect.bottom = catDesc.Height * 6;

In the Game.cpp file, modify in the TODO section of Render:

m_spriteBatch->Begin(SpriteSortMode_Deferred, nullptr,
      m_states->LinearWrap());

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, &m_tileRect,
    Colors::White, 0.f, m_origin);

m_spriteBatch->End();

Build and run to see the sprite as an array of 4x4 cats.

Screenshot of cat sprite

Technical Notes

By default SpriteBatch uses a LinearClamp sampler. In order to do the tiling, we had to override that setting by providing a different LinearWrap sampler.

Stretching a sprite

Using the optional destination rectangle instead of a 2D position, we can stretch a sprite.

In the Game.h file, add the following variable to the bottom of the Game class's private declarations:

RECT m_stretchRect;

In the Game.cpp file, add to the TODO section of CreateWindowSizeDependentResources:

m_stretchRect.left = size.right / 4;
m_stretchRect.top = size.bottom / 4;
m_stretchRect.right = m_stretchRect.left  + size.right / 2;
m_stretchRect.bottom = m_stretchRect.top + size.bottom / 2;

In the Game.cpp file, modify in the TODO section of Render:

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_texture.Get(), m_stretchRect, nullptr,
    Colors::White);

m_spriteBatch->End();

Build and run to see the sprite blown up

Screenshot of cat sprite

Drawing a background image

Our last exercise for this lesson is rendering a sprite as a full background image. Start by saving sunset.jpg to your project directory, and then from the top menu select Project / Add Existing Item.... Select "sunset.jpg" and click "OK".

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

RECT m_fullscreenRect;
Microsoft::WRL::ComPtr<ID3D11ShaderResourceView> m_background;

In Game.cpp, add to the TODO of CreateDeviceDependentResources:

DX::ThrowIfFailed(
    CreateWICTextureFromFile(device, L"sunset.jpg", nullptr,
    m_background.ReleaseAndGetAddressOf()));

In Game.cpp, add to the TODO of CreateWindowSizeDependentResources:

m_fullscreenRect = m_deviceResources->GetOutputSize();

nd then modify the m_origin initialization back to:

m_origin.x = float(catDesc.Width / 2);
m_origin.y = float(catDesc.Height / 2);

In Game.cpp, add to the TODO of OnDeviceLost:

m_background.Reset();

In Game.cpp, modify the TODO section of Render to be:

m_spriteBatch->Begin();

m_spriteBatch->Draw(m_background.Get(), m_fullscreenRect);

m_spriteBatch->Draw(m_texture.Get(), m_screenPos, nullptr,
    Colors::White, 0.f, m_origin);

m_spriteBatch->End();

Build and run to see our cat drawing over a sunset background.

Screenshot of cat sprite

Technical note

If we were only drawing the background (i.e. a single 'sprite' that fills an entire viewport), then using BasicPostProcess's Copy operation is faster than SpriteBatch, but requires Direct3D Hardware Feature Level 10.0 or later.

Next lesson: More tricks with sprites