On Tue, Jul 8, 2014 at 9:20 AM, Elise Huard <haskell@elisehuard.be> wrote:

I wanted to thank you, because pointing to unsafeCoerce was a nice bit
of serendipity. I'll admit I thought it was nitpicking initially, but
I did a quick pass at cleaning things up last week after your mail
(not perfect, but this was a prototype so I'm not looking for pretty):

https://github.com/elisehuard/game-prototype/commit/5cf85fa60f325dbe610b5e1f017c9427e304daf6

and that fixed the texture mapping!
Consider me informed on that issue :)

Cool! By the way, the 'proper way' to convert between Double and CDouble is to use realToFrac:

Prelude Foreign.C.Types λ> realToFrac (1 :: Double) :: CDouble

1.0

In specific case like this (Double <-> CDouble) it should be equivalent (but as a user of the library you shouldn't depend on know that). In some cases it can be a performance hit, but that's what RULEs pragmas are for. Moreover, some versions of the Haskell OpenGL bindings made it so that GLdouble was not the same type as CDouble. So the safest way is to use realToFrac and depend on the library writer to provide RULEs that make it efficient.

I hope that helps,

Jason