Generic resource loading

[z33ky]

To load resources like textures and models from the ARC files, a templated resource class was proposed:

template<typename Header> // where Header is sh3_texture_header for example
class resource
{
    ...

    Header& header() { return reinterpret_cast<Header&>(raw.front()); }

    using iterator_range = std::pair<raw::iterator, raw::iterator>; // we could use boost::iterator_range instead
    iterator_range data() { return std::make_pair(begin(raw) + header().data_offset(), end(raw)); }

    ...

    std::vector<uint8_t> raw;
};

A texture would then be a resource<sh3_texture_header>, which provides us access to the header by simply aliasing the bytes in resource::raw , as well as convenient access to the "body" (non-header bytes). Reading in the vector is then enough to load a resource from a file.

Some resource types, e.g. models, may have multiple sub-headers. This is what the data_offset() function of the header is for. For headers without sub-headers, the implementation is just return sizeof(*this);, while for those with sub-headers, the implementation is return sizeof(*this) + num_sub_headers * sizeof(SubHeader); to account for them. The sub-headers in models refer to embedded textures. These resources can also be handled with an appropriate data_offset() function.

[Quaker762]

This is in place of vfile yes? So instead of having a buffer that we seek and read data from (similar to how an actual FILE works), we just have a resource with appropriate header passed in that we can more easily read bytes from the header (without a local copy in a Load( ) function). Is there any advantage to this besides the added abstraction of the header types? If this is in place of vfile, would it work considering the Master File Table (arc.arc) is just a whole lot of folders and files shoved into one huge file??

EDIT: I've just reread #43 and I think I may have the wrong idea about this (it also midnight here and my reading comprehension isn't so good)

[z33ky]

A vfile provides access to a file in the MFT as bytes, while this would interpret the bytes as a resource. So it doesn't necessarily make vfile obsolete (at least in the short term), but would definitely be used in place of it.

Since the resource includes a local buffer (raw), just like the vfile, I don't see why it would conflict with the workings of the MFT.

[Quaker762]

Okay, I think I see now. It's basically a better way to abstract the resource type and also saves a heap of code reuse (such as having heaps of calls to file.ReadData(...)) as the data is already there for us to access.

Also, I assume data_offset() would work with the convoluted model format (IIRC there's a header for each primitive/polygon) where we have to iterate over n primitives? If so that would definitely make loading models much easier and less complex.

[z33ky]

It's basically a better way to abstract the resource type and also saves a heap of code reuse (such as having heaps of calls to file.ReadData(...)) as the data is already there for us to access.

Exactly.

Also, I assume data_offset() would work with the convoluted model format (IIRC there's a header for each primitive/polygon) where we have to iterate over n primitives? If so that would definitely make loading models much easier and less complex.

data_offset() can use all fields in the header to calculate the appropriate offset, e.g. num_sub_headers in the second example. If more information is required, we'll need to think if we can perhaps pass this to data_offset() from the resource via parameter.

This is only a concept so far. I have not started the implementation, this issue represents only the idea.

[Quaker762]

Excellent, this sounds like this could work really well. Hopefully you can find a workaround for some of the weird formats (i.e models). You should be able to see what I mean by looking at Mike's code I sent you.