Question

I’m using JuicyPixels to load PNGs fron on-disk, and I need a pointer to the raw pixel data. It is stored as a UArray in JuicyPixels. How do I get said pointer? Is it as simple as “casting” to a StorableArray? If so, how?

Answer 1

You can use thaw in IO:

do storableArray <- thaw uArray
   ...

This copies the entire array, but probably more efficiently than hand-written code to do the same. If you know you’re not going to access the UArray again, then you can use unsafeThaw, but with current library implementations, it’s still likely to cause a complete copy. (The array types that have a non-copying implementation of unsafeThaw are listed in its documentation.)

There might be an unportable way to get at the raw pointer underlying a UArray, but I couldn’t find one in GHC.Exts.