Optimized Surface Shaders

The approxview directive for shaders that use view direction (i.e. Specular) makes the view direction normalized per vertex instead of per pixel. This is approximate, but often good enough.
The halfasview for Specular shader types is even faster. The half-vector (halfway between lighting direction and view vector) is computed and normalized per vertex, and the lighting function receives the half-vector as a parameter instead of the view vector.
noforwardadd makes a shader fully support one-directional light in Forward rendering only. The rest of the lights can still have an effect as per-vertex lights or spherical harmonics. This is great to make your shader smaller and make sure it always renders in one pass, even with multiple lights present.
noambient disables ambient lighting and spherical harmonics lights on a shader. This can make performance slightly faster.

Precision of computations

For world space positions and texture coordinates, use float precision.
For everything else (vectors, HDR colors, etc.), start with half precision. Increase only if necessary.
For very simple operations on texture data, use fixed precision.
PC 一般都是仅使用 float 的
Mobile 一般都是仅使用 half 的
除了老显卡会支持使用 fixed，大部分都是直接使用 half

However, on PowerVR GPUs found in iOS and some Android devices, alpha testing is resource-intensive. Do not try to use it for performance optimization on these platforms, as it causes the game to run slower than usual.

On some platforms (mostly mobile GPUs found in iOS and Android devices), using ColorMask to leave out some channels (e.g. ColorMask RGB) can be resource-intensive, so only use it if really necessary.