The passed inX and inY x/y offset for readPixel -> [textureData] buffer,
must be passed to readTexture.updateSubImage(..)'s destination offset.
I.e. the buffer's content starting at beginning is filled via glReadPixels
w/ offset applied.
Hence the texture update must pass the offset as the destination offset,
i.e. to be used for glTexSubImage2D's offset.
Currently zero is passed.
fixed as described