Implementation

Naming conventions

While the DirectX Tool Kit design is heavily influenced by the XNA Game Studio framework C# object design, it uses C++ conventions consistent with modern Win32 APIs rather than the strict .NET use of PascalCase as enforced by FXCop.

• PascalCase for class names, methods, functions, and enums.
• camelCase for class member variables, struct members
• UPPERCASE for preprocessor defines (and nameless enums)

The library does not generally make use of Hungarian notation which as been deprecated for Win32 C++ APIs for many years, with the exception of a few uses of p for pointers and sz for strings.

SAL annotation

The DirectX Toolkit library makes extensive use of SAL2 annotations (_In_, _Outptr_opt_, etc.) which greatly improves the accuracy of the Visual C++ static code analysis (also known as PREFAST). The standard Windows headers #define them all to empty strings if not building with /analyze, so they have no effect on code-generation.

The pImpl idiom

DirectXTK's implementation makes extensive use of the pImpl idiom. This keeps the public headers slim and minimizes inter-module dependencies.

// SpriteBatch.h public header
class SpriteBatch
{
public:
    SpriteBatch(...);
    SpriteBatch(SpriteBatch&& moveFrom);
    SpriteBatch& operator= (SpriteBatch&& moveFrom);

    SpriteBatch(SpriteBatch const&) = delete;
    SpriteBatch& operator=(SpriteBatch const&) = delete;

    virtual ~SpriteBatch();
    ...

private:
    // Private implementation.
    class Impl;

    std::unique_ptr<Impl> pImpl;
};

This also allows use to allocate the pImpl class internally using _aligned_malloc(x,16); so that we can use the DIrectXMath aligned XMVECTOR and XMMATRIX types directly in the implementation across all architectures.

Calling-conventions

The std::function is used for callbacks as a general pattern so that client code can provide function pointers, lambdas, functors, etc. To support building with a mix of calling conventions, we need to annotate the std::function correctly.

HRESULT __cdecl SaveWICTextureToFile( /*...*/,
    std::function<void __cdecl(IPropertyBag2*)> setCustomProps
        = nullptr );

Note: std::function doesn't support using __vectorcall until VS 2015, so use of /Gv is difficult in VS 2013 or earlier.

Default constructors/assignment operators

The C++11 standard includes a more efficient =default and =delete construct for dealing with default constructors and assignment operators. This is not supported until VS 2013.

For example, to prevent copying we use:

// Prevent copying.
SpriteBatch(SpriteBatch const&) = delete;
SpriteBatch& operator= (SpriteBatch const&) = delete;

Note that use of =default and =delete can improve codegen for derived types.

DirectXMath Parameter Conventions

The library uses the DirectXMath calling convention types to improve parameter passing of XMVECTOR and XMMATRIX types.

Further Reading

Dual-use Coding Techniques for Games