Add/Test/Change native support for passing arrays of Entity to webgl

[TheSeamau5]

So, while I was working on Graphics Engine (my 3d engine based on elm-webgl), I realized that Lists were very slow as an internal representation for my scene objects. Switching to Array gave me a HUGE performance boost (which was kinda unexpected cuz I tested on pong, which has just 4 scene objects: 2 paddles, 1 ball, and 1 background).

But to do that, I have to call toList at one point so that I may pass the data onto webgl as it expects a List Entity as its argument.

It would be nice if there were a version where I could pass an Array Entity instead. I'm not saying this to save me from writing one word. I'm wondering if this would bring a nice speed-up to elm-webgl. At the very least, it would be nice to test the two functions side by side on the same exact code to see if there's a noticeable difference.

[evancz]

I'm one of the collaborators on this project, but I'd say you have a better understanding of the performance implications. If you can mess around with the code here and show that it does give a nice performance boost, I think it'd make sense to merge something in.

After we have some concrete examples that display the difference, we can think about what the API for this might look like.

[TheSeamau5]

Ok, cool. I'll try it out. I noticed that the js code just calls List.map, so, hopefully the changes will be minimal. I'll let you know as soon as I'm done.

[johnpmayer]

Sorry for being absent. Do arrays have a native foreach construct? That's
really all webgl uses, frankly.
On Jan 21, 2015 5:50 PM, "Hassan Hayat" notifications@github.com wrote:

Ok, cool. I'll try it out. I noticed that the js code just calls List.map,
so, hopefully the changes will be minimal. I'll let you know as soon as I'm
done.

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[TheSeamau5]

Cool! I got it to work with array. It was as I thought, just a few changes in the JS code. I just tried it on this example and it works. The thing is that given that not much is going on so, in both cases, very few resources are being used. I'll try to come up with a big example, like spawing a whole bunch of crates or something

[rhaps0dy]

Any progress on this? I had serious performance issues with elm-webgl, and most of the time is spent mapping to push attributes to GPU (the eval I added in #24 was about half of the slowness though).

[johnpmayer]

Trying to understand this issues as well. Does changing the argument to Array (in the WebGL library) result in a significant speedup, or does the speedup just come from switching the representation in your model to Array?

[rhaps0dy]

In my experience, the biggest delay when using lists was map. The function would follow all the pointers from the linked list (not on cache, slow) and call push to the Javascript array before passing that to WebGL.

The conversion from Elm Array to Javascript Array is probably faster