Microsoft DirectX 9.0

Hardware Abstraction Layer

Microsoft?Direct3D?provides device independence through the hardware abstraction layer (HAL). The HAL is a device-specific interface, provided by the device manufacturer, that Direct3D uses to work directly with the display hardware. Applications never interact with the HAL. Rather, with the infrastructure that the HAL provides, Direct3D exposes a consistent set of interfaces and methods that an application uses to display graphics. The device manufacturer implements the HAL using 32-bit code with Microsoft Windows?XP, Microsoft Windows NT? and Windows 2000. Windows 98 and Windows Millennium Edition (Windows Me) use a combination of 16-bit and 32-bit code. The HAL can be part of the display driver or a separate dynamic-link library (DLL) that communicates with the display driver through a private interface that the driver's creator defines.

The Direct3D HAL is implemented by the chip manufacturer, board producer, or OEM. The HAL implements only device-dependent code and performs no emulation. If a function is not performed by the hardware, the HAL does not report it as a hardware capability. Additionally, the HAL does not validate parameters; Direct3D does this before the HAL is invoked.

In Microsoft DirectX?9.0, the HAL can have three different vertex processing modes: software vertex processing, hardware vertex processing, and mixed vertex processing on the same device. The pure device mode is a variant of the HAL device. The pure device type supports hardware vertex processing only, and allows only a small subset of the device state to be queried by the application. In addition, the pure device is available only on adapters that have a minimum level of capabilities.

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