DirectX and OpenGL are two graphics application programming interfaces, or APIs, that help Google Earth generate high-quality 2D and 3D images. Google Earth relies upon these two APIs to provide a layer of abstraction between the application and the many possible combinations of operating systems, microprocessors and graphic processing units, or GPUs, on which the software may run.
DirectX is a proprietary graphics API for devices running Microsoft's Windows operating systems. DirectX is a graphics rendering specification rather than an application, utility or hardware driver. Graphics card manufacturers can include hardware support for DirectX that Google Earth can utilize to generate realistic, high-resolution, 3D images, as well as smooth simulations, scene transitions and animations.
OpenGL is a platform-neutral, open API for rendering graphic images. Although the API is different, OpenGL provides Google Earth with the same graphics performance enhancements as DirectX. OpenGL was originally developed by Silicon Graphics Incorporated. Today, however, the OpenGL API is maintained by the non-profit Khronos Group. The OpenGL specification is freely available for GPU manufacturers and software developers to incorporate into their products.
Graphic Card Requirements
Google does not specifically recommend either DirectX or OpenGL for Google Earth. You can configure Google Earth to operate in either DirectX or OpenGL rendering modes. If your system crashes or performs poorly in one mode, Google recommends you switch to the other mode. Nevertheless, both the minimum and recommended system requirements for Google Earth specifically include a graphics card with DirectX9 support.
Since the DirectX API is designed for PCs running Windows operating systems only, Linux and Mac OS X users must run in OpenGL mode. Although the OpenGL API is freely available to use without licensing restrictions, many GPU manufacturers choose to provide direct hardware support for DirectX only. If your GPU supports OpenGL, Google Earth should render graphics with the same speed and quality of a DirectX-compatible GPU. If your GPU supports only DirectX and you are a Linux or OS X user, however, Google Earth will emulate an OpenGL-compatible GPU in software. Software emulation lowers image quality and rendering speed.
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