You can play/experiment with Corona custom (fragment) shaders from a webgl-enabled browser. This includes being able to write your own shader code and live previewing them, among other things:
https://shader.coronalabs.com/
To share the shader code, click “Generate share link”
Since Lua means “moon” in Portuguese, here’s one of a rotating moon:
Ah, cool. 
How far is the compiler from what would show up in an HTML5 build?
I’ll test my fragment-only shaders when I get the chance.
Argh, looks like more of mine depend on vertex shaders than I thought. 
(Also, I have some “outline” ones that are rather pointless with opaque textures.)
That said, all the fragment-only ones seem to work well:
Circle (basic) (This is meant to be put on a circle display object; it doesn’t bother to discard outside pixels.)
Simplex2 (basic) (Basically the same one from the other thread / Code Exchange; noise adapted from Ashima Arts)
Sphere (basic) (The circle one, but discarding)
Sphere (fractional Brownian motion) (Everything from here on is adapted from Ashima Arts and / or Stefan Gustavson)
A lot of the noise samples aren’t time-dependent, but have time-updated parameters in the associated demos (and look pretty cool).
N.B. If you fiddle with the CoronaVertexUserData parameters in certain effects, a few will interpolate REALLY weirdly since they consist two [0, 1]-range numbers encoded together (fun with cramming into four values!). 
Really cool!
