Reproduce a bug with SNCShadable where the Metal shader code that gets generated has errors that make the shader fail.
The code works well on non Metal devices (simulator, iPhone 5c) but not on Metal devices (iPhone 6).
On the left: desire output, on the right: error
The code fails with error: redefinition of parameter 'u_diffuseTextureSampler'
u_diffuseTextureSampler is defined once here: https://github.com/gsabran/SCNShadableBug/blob/master/debug.log#L543
and gets defined a second time here https://github.com/gsabran/SCNShadableBug/blob/master/debug.log#L570
The second definition seems to come from the Metal compilation of the shader snippet that refers to u_diffuseTextureSampler but doens't define it.