[SOLVED] Material State Changes

[BrightBit]

Hello everyone,

do you guys know Runescape? The models of this browser game are coloured entirely by their material attributes. The artists didn't use textures.

I learned that state changes (in relation to textures, materials, shaders, etc.) can be a performance issue. I understand that changing a whole texture takes time but I don't understand that changing some floats for e.g. the diffuse material attribute would be an impact on performance. So my question is:

Even if a model consists out of for instance 15 different materials (and all these materials got no texture), would that really be that expensive?


Greetings
BrightBit

Edit: Removed image.

[betajaen]

Couldn't you have a colour per vertex? If you do it that, with one material, one sub-mesh, it's one batch.

[BrightBit]

Thanks for the fast answer. Are vertex colours also supported on older machines? Especially on computers with graphic cards without programmable shaders?

Nevertheless I'm still curious about the first question. Why does it take that much time for "small" material changes?

[Praetor]

Vertex colors will be supported on pretty much any machine you can get now, or could get in recent years.

As for the question you had. State changes mean communication to the video card. Since the GPU is a separate from the CPU the communication must go through a bus. The driver can help by being clever with how it sends instructions over, but what it means is each time you tell the GPU to change something to prepare for a draw, commands have to be sent from one component of your computer to another. This is essentially why state changes are "slow."

[_tommo_]

Thanks for the fast answer. Are vertex colours also supported on older machines? Especially on computers with graphic cards without programmable shaders?

Nevertheless I'm still curious about the first question. Why does it take that much time for "small" material changes?

Mario in Mario64 was entirely coloured with vertex colours.
This to say, that vertex colours are supported even where textures aren't
They are also much faster because the vertex data is "already there", while textures have to be explicitly fetched from memory.

[BrightBit]

Thank you guys. Especially Praetor for the answer on state changes.