https://github.com/Microsoft/DirectXTK/wiki/Sprites-and-textures
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 first two lessons: The basic game loop and Adding the DirectX Tool Kit which we will use for this lesson.
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 m_texture;
In Game.cpp, add to the TODO of CreateDevice:
DX::ThrowIfFailed(
CreateWICTextureFromFile(m_d3dDevice.Get(), 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.
Troubleshooting: 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 m_spriteBatch;
DirectX::SimpleMath::Vector2 m_screenPos;
DirectX::SimpleMath::Vector2 m_origin;
In Game.cpp, modify TODO of CreateDevice to be:
m_spriteBatch = std::make_unique(m_d3dContext.Get());
ComPtr resource;
DX::ThrowIfFailed(
CreateWICTextureFromFile(m_d3dDevice.Get(), L”cat.png”,
resource.GetAddressOf(),
m_texture.ReleaseAndGetAddressOf()));
ComPtr 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 CreateResources:
m_screenPos.x = backBufferWidth / 2.f;
m_screenPos.y = backBufferHeight / 2.f;
If using the UWP template, you also need to add m_spriteBatch->SetRotation(m_outputRotation); to handle display orientation changes.
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 m_states;
In Game.cpp, add to the TODO of CreateDevice:
m_states = std::make_unique(m_d3dDevice.Get());
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 CreateDevice and change our use of CreateWICTextureFromFile to CreateDDSTextureFromFile:
DX::ThrowIfFailed(
CreateDDSTextureFromFile(m_d3dDevice.Get(), 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 CreateDevice:
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
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 m_background;
In Game.cpp, add to the TODO of CreateDevice:
DX::ThrowIfFailed(
CreateWICTextureFromFile(m_d3dDevice.Get(), L”sunset.jpg”, nullptr,
m_background.ReleaseAndGetAddressOf()));
In Game.cpp, add to the TODO of CreateResources:
m_fullscreenRect.left = 0;
m_fullscreenRect.top = 0;
m_fullscreenRect.right = backBufferWidth;
m_fullscreenRect.bottom = backBufferHeight;
and 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