Portability

Deprecated

Portability refers to the ability to render a scene, including all its hardware shaders, on a wide range of graphics hardware. This is not easy since graphics hardware from two different vendors, or even successive hardware generations from the same vendor, can vary drastically. This can be easily solved by either supporting a common subset of all hardware variants, or by requiring a different shader implementation for each variant. Neither is desirable, although it must remain possible to tailor a shader for a specific hardware or application.

mental ray is designed to separate hardware-dependencies from scene modeling as much as possible.

There are six architecture levels:

The shader level is the domain of artists who design the scene. Like with all shaders, the artist needs to be aware of their functionality and limitations, but there is no need to be aware of the underlying hardware. In fact, many of these shaders have both a hardware and a software version.
The shader declaration (and implementation) are performed by a programmer who designs new shaders. As described above, shader declarations differ between hardware and software shaders. Some declarations are provided by mental images; others may be written by customers. This requires programming skills.
The hardware declaration describes a specific graphics hardware. There are different declarations for various NVIDIA, ATI, and other boards. In principle, new hardware requires only changing the hardware description, although additional hardware capabilities might make possible more sophisticated shaders.
The mental ray infrastructure is provided by mental images. It is hardware-agnostic as much as possible, and mainly concerned with interpreting declarations and mapping rendering requests to OpenGL calls.
The graphics hardware is the physical graphics board plugged into the computer.

The hardware declaration describes the capabilities of the installed board. Much of this can be read directly from the board; OpenGL provides various information about which features are supported by the board, and hardware limits such as the size of shaders, size of texture memory, or the number of uniform variables. Some items remain under user control through the hardware declaration, such as symbolic register mappings and directories to search for shader declaration files.