Performance issue when loading individual tiles

[thejohnhoffer]

What I observe

For each loaded tile, this line in _readRaster copies every image pixel from the tile buffer one-by-one. Each of our tiles (1024px by 1024px) therefore call this function over a million times when loaded. For our case of direct rendering of hundreds of tiles, This produces a 4x slowdown compared to a direct copy from tile buffer to typed array.

What I expect

Only one buffer to array conversion should be needed to read one tile that byte-for-byte matches an IFD.

Proposed solution

PR #348