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In computing, D3DX (Direct3D Extension) is a high level API library which is written to supplement Microsoft's Direct3D graphics API. The D3DX library was introduced in Direct3D 7, and subsequently was improved in Direct3D 9. It provides classes for common calculations on vectors, matrices and colors, calculating look-at and projection matrices, spline interpolations, and several more complicated tasks, such as compiling or assembling shaders used for 3D graphic programming, compressed skeletal animation storage and matrix stacks. There are several functions that provide complex operations over 3D meshes like tangent-space computation, mesh simplification, precomputed radiance transfer, optimizing for vertex cache friendliness and strip reordering, and generators for 3D text meshes. 2D features include classes for drawing screen-space lines, text and sprite based particle systems. Spatial functions include various intersection routines, conversion from/to barycentric coordinates and bounding box/sphere generators.
The D3DX library contains pre-written routines for doing things common to most 2D/3D applications, such as games. Since the Direct3D API is relatively low-level, using the D3DX library is usually much simpler.
In 2012, Microsoft announced that D3DX would be deprecated in the Windows 8 SDK, along with other development frameworks such as XNA. Shader effects, texture management, and mesh models are available through DirectX Tool Kit, a source code library published through CodePlex.   The mathematical constructs of D3DX, like vectors and matrices, would be consolidated with XNAMath into a new library, DirectXMath,
The ID3DXEffect interface is used for compiling and binding FX shaders (.fx). It supports automatic mapping of named shader parameters to hardware constant registers, parameter pools, mapping textures to available samplers, specifying 'techniques' and modifying render states.
The ID3DXFont interface can be used to draw 2D text. See also D3DXCreateText that creates 3D meshes of text.
The ID3DXLine interface can be used for drawing anti-aliased screen-space lines with pattern.
The ID3DXMesh interface is used for storage of meshes and mesh optimization for vertex cache friendliness and strip reordering. Some functions in D3DX operate on this interface. An example is D3DXComputeTangentFrame for creating a tangent-space frame for effects like normal and parallax mapping. A descendant of this class is ID3DXPMesh that can do geometry simplification.
It is used for Precomputed Radiance Transfer - a technique similar to spherical harmonics lighting that is used for precomputed global illumination and soft ambient lighting.
The ID3DXSprite interface is a C++ class used for drawing a 2D image to the screen known as a sprite in computer graphics. In DirectX 7 this was typically done using the DirectDraw API, which is deprecated.
The programmer typically needs only to call the ID3DXSprite object's Begin() method to set up the render state and world transform for 2D drawing, call the Draw() method to add textures to the list to be drawn and finally call the End() method to draw the images to the screen and restore the original graphics state.
A common criticism of the D3DXSprite was that it was slow but this issue has been addressed as of Direct3D 9.
Computes the tangent-space frame of a mesh that is used for effects like normal/bump mapping, parallax mapping and anisotropic lighting models. It handles vertices at tangent-space discontinuities by making duplicates, thus solving the hairy ball problem. It doesn't handle reversed UV winding of faces so models with mirrored texture mapping may run into lighting troubles because of this.
- Microsoft. "Where is the DirectX SDK?". MSDN. Retrieved 18 October 2012.