What Is D3dx9

Function
D3dx9_31.dll is part of the DLLs associated with Microsoft's DirectX 9 APIs. The '3d' in the file name indicates that its function supports the Direct3D API, which in turn is used to support 3-D graphics and multimedia within the Windows environment. DirectX is a group of APIs used by Windows to allocate resources efficiently when carrying out multimedia and 3-D gaming tasks.
Location Within Windows
This DLL resides in the Windows System folder (by default, C:\WINDOWS\system32). If D3dx9_31.dll is missing it may have been deleted, moved, or renamed from this location. You may have to download D3dx9_31.dll and move it to this location to restore functionality.
Most Common Error
The most common D3dx9_31.dll error occurs when it is missing or has become corrupted. If this is the case, you will most likely see an error when launching a DirectX 9 game. The problem can be easily solved by downloading the DLL and placing it in the appropriate folder. Check the resources for a download link to D3dx9_31.dll.