Performance cost of double sided material: not visible in stats?

[anonymous_user_9d5e1743]

One question before more answers: are your characters going to have LoDs? Because if yes, usually you prepare even cheaper materials for far distance, and the most expensive ones for near distance. Than there is other approach which I love to talk about, since we are going to have a presentation from Ryan Brucks about this soon, is the actual use of impostors for very far meshes, which I think you can use even for characters that are not even moving, and then use the regular LoD system when they are moving.

So there are so many options… hard to tell if it is generic, but the best way to understand the impact is the actual use case… you said said about having “many characters onscreen” it helps but a better info would be number of tris per char x number of instances x number of materials per char, not matter at first analysis if it is double sided or not, but might evolve depending on the numbers to actually get them into account.

Well… thats the plan, for the future in which I hopefully have time to generate the LODs. As you can see from this answer, maybe I should be LESS concerned about optimizing my character meshes for performance right now as I plan to omit LODs until later… probably should simply not worry about it at the moment.

Imposters sound EXACTLY like what I would have planned for the highest/lowest LOD (never sure where you start counting with LOD :)) … A simplebillboard with the coarse outline of the character for distances where it would be hard to see even simple animations. Very interested about this presentation… will it be available online?

About the numbers: The idea was to create a very detailled looking art style, in spirit mimicking the old 2D isometric RPGs with extremly detailed 2D characters. Thus the characters would have a rather high poly count for characters seen from an isometric perspective (so that characters look good even in 4k), which I plan to make up for with aggressive LODs for characters further away to keep the polycount low.

Currently I am aiming for 6000-8000 tris for a humanoid character. Current rather conservative plan is to allow for around 100 characters onscreen max. Of course, not all of them in the highest LOD… I might create the lower LODs “by hand” and replace the geometry that needs the double sided material for the highest LOD there, so the double sided material would only be used for the highest LOD (which would also have the highest tris count, but would only be active for a small percentage of characters on screen as its a “pseudo-isometric” view).

Would you reckon the impact of having 6000-8000 double sided tris, and only one material is way higher than having only 2000-3000 double sided, and 4000-5000 one sided ones, but in two separate materials, given there might be 20-30 such characters in the highest LOD on screen max at any given time?

Personally, I do my best to optimize pixel rendering cost. Optimizations here allow games to run faster at higher resolutions and yield the most dramatic performance improvements, especially on middle-higher end hardware. Draw calls are more of a constant overhead that affects lower end users more than anyone else. Still important in D3D11, but no where near as much in D3D12, Vulkan, and Metal. Unfortunately, Vulkan is still not stable enough to develop for right now.

Even if you have a lot of characters you can certainly get away with two material separations, take advantage, and make a nicer, more appropriate cloth shader. But that all depends on your desired fidelity and number of characters: a truly proper character needs a special model for hair, eyes, skin, cloth, and accessories as all these components require radically different shading models from each other. The eye alone typically requires separate shaders too, if you break it down far enough.

How many characters are in your project, what platforms are you targeting, and what fidelity are you trying to achieve?

Okay, good points. I also was under the impression that drawcalls where no longer as important in more modern rendering pipelines than in DX9… Given that this is just a prototype and still years away from any kind of release, probably should stop trying to work around DX9/DX11 problems.

As for the fidelity/style: the characters look quite realistic, but I am not targetting real photorealism. Thus I don’t care too much about small incosistencies with lighting and shading… all the textures will be hand-drawn, so trying to go for a 100% realistic look would probably increase the problems with textures looking off. So, as said, I am less concerned about using hair and eye shaders and all of that. From the distance the characters are seen, and in the environment using my textures, they look perfectly fine using a simpler subsurface shader.

Now, I of course decided that while starting the project in Unity, where AFAIK draw calls have a way higher impact than in Unreal 4. So my decision to move everything into a single material was motivated by the technical necessity as well as not seeing a visual problem with it. If I could use 3 or 4 materials “for free”, thus without impact, I probably would look into what the eye, hair and skin shader could offer (though aren’t all these shaders more “expensive” performance wise?).
Sticking with that idea, is it possible, and wise, to have a single texture atlas mapped to different UV materials? Thus have the eyes in the same texture map as the hair? Or does it make more sense to create a hair atlas for different characters, and share the materials between the different character’s hair geometry? I am a little wary of having to many extra textures for small things like eyes, or strands of hair. I guess that is fine for games were characters will fill the whole screen during a cutscene anyway, but for what I plan to do, this seems overkill.