VertexData Cache

[john-chapman]

• Reduce draw cost for high order primitives by caching vertex data (+ primitive type).
• Each cache maps to an ID.
• Expose this system to the user e.g. BeginCache(_id);, EndCache(), DrawCache(_id) (but with better names).
• Cached vertex positions are transformed by the current draw state as they are copied into the final buffer.
• Transform other properties of the cached data (size/color).

[ChemistAion]

I was wondering if there have been any updates or progress made since?

[john-chapman]

I've not really looked into this since the issue was created, but I think it would be quite simple to implement an initial version. Updated thoughts:

The main goal here would be to provide an API allowing the user to avoid the overhead of making lots of Im3d calls. User code would look like this:

if (Im3d::BeginCache("BigScene")) // If false, we skip Im3d calls below and use the cached vertex data directly.
{
    // ... lots of Im3d calls here.

    Im3d::EndCache(); // Cache the vertex data we just created.
}

Internally, cached vertex data would follow the structure of m_vertexData (= one list per layer, per primitive * 2 for sorted/unsorted). This way, the cache can be copied into m_vertexData such that sorting/layering still works. There would also be an InvalidateCache(id) function.

The approach outlined above has a couple of caveats:

Transform modification:

• Could store the top of the transform stack per cache, if it's different when we go to copy the cached data we can re-transform the data there.
• That would only support a single global transform modification per cache. Anything more complicated requires invalidating the cached data.

Nested caches:

• Nested caches won't invalidate properly, as the nested cache data will effectively be duplicated in the enclosing cache.
• Could potentially solve by storing a list of nested caches per cache. Invalidating a cache would also invalidate any referents.