* Half-floats and floats are usable in ES2 / WebGL 1 (they weren't by
mistake) -- just use OES_texture_float or OES_texture_half_float.
* Half-floats are linearly filterable in ES3 / WebGL 2 and
OES_texture_half_float_linear makes it possible in ES2 / WebGL 1.
* Floats are not linearly filterable, not even in ES3 (they were by
mistake) -- one needs OES_texture_float_linear for that.
* Neither floats nor half-floats are renderable in ES < 3.2 -- one
needs EXT_color_buffer_half_float or EXT_color_buffer_float for that.
The former is available for example on iOS, the latter is apparently
only on NV cards. Both are builtin in ES 3.2, EXT_color_buffer_float
depends in ES3, so half-floats are the only possible format to render
to in ES2.
* Rendering to floats in WebGL is slightly more complicated --
unlike with OpenGL ES 2 it's possible to render to floats in WebGL 1
using WEBGL_color_buffer_float. There's another WebGL 1 extension
called EXT_color_buffer_half_float and they are both replaced with
EXT_color_buffer_float in WebGL 2.
And, as a cherry on top, GPH (formerly SGI) has patents on most of
these, which is probably why the support for them is so spotty.
Vladimír Vondruš
