Atmospherics

[mikeman]

Hey, I thought we were going for cool(per-pixel) looking fog, imagine how would it look if we made volumes of fog divided into boxes.

 

Anyway, Roja required 3 types of fog, and I don't think we need true 3D volumetric for for any of them.

 

1) Regular all-around fog. OpenGL handles that.

2) Smoke coming off the ground. A good particle system can take care of that.

3) Fog beneath your feet: It's a simplified version of volumetric fog, since everything below a plane (y=C) is fogged. You can use glFogCoordEXT or a very simple vertex shader for this, no extra passes.

[Entropy]

Well, you are teh expert, so do it as you think it's best.

But I really don't think it's a good idea to make the fog with particles. We'd need a LOT of them, for a good looking fog.

[Lachesis]

I'm thinking the best idea is to use vertex shaders, since they're supported all the way down to GF2(even in software, they're fast). In that case, any special effect is simply reduced to writing a special vertex shader for it. For instance, for "fog below your legs", you simply calculate the distance between the vertex and a horizontal plane, and set the fog accordingly.

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That sounds great, mikeman, it's exactly what we need. If you know a good guide to vertex shaders, just post it here, please.

 

P.S. After reading a bit, I wonder whether a fragment shader would suit that purpose better?

Edited May 26, 2005 by Lachesis

[Lachesis]

P.P.S I learned more and I think we could go without a fragment shader and use a plain vertex shader. However, that vertex shader would have to be applied to the whole (3D) scene. Since we don't know what OpenGL features are used by Cal3D in advance, I suspect it would have to support quite a comprehensive featureset regarding textures, normals, materials, lighting and whatever else it is replacing. I have never written one line of GPU programming, so this task is way too complex for me. If I had the GLSL source of a vertex shader that does everything like OpenGL would do when not using the shader it would be easy to modify it, but without I'm afraid I can't.

 

With regards

Lachesis

[mikeman]

Ok, once and for all: Cal3d doesn't change a thing. I have a function cal_render_actor(). All it does it gets the vertex,texture coordinate and normal data and renders them. Nothing more. Exactly the same as every other model in the game. Don't worry about that.

 

But it's true that if you use vertex shaders you need to replace the whole fixed pipeline(tranformations,texgen,lighting...) too.

 

I'm wondering if 2 rendering passes aren't so bad after all: First we render the scene normally, to achieve texturing,shadows and lighting. The second pass(with vertex shaders) will be with texturing,lighting and shadows off, so it will be much faster and only implement the desired effect. The shader will look like this:

 

uniform vec3 fog_point;//A point in the fog plane(eye space)
uniform vec3 fog_norm;//The normal of the fog plane(eye space)

void main()
{
 vec4 V_eye;
 float distance;

 V_eye=gl_Vertex*gl_ModelViewMatrix;
 distance=dot( (V_eye.xyz-fog_point), fog_norm);//signed distance from the fog plane

 gl_Position=ftransform();//Emulate the fixed pipeline to avoid z-fighting
 gl_FrontColor=vec4(0,0,0,0);
 gl_FogFragCoord=distance;
}

 

Something like that anyway. Maybe sampling a 1D fog texture would give better quality.

Edited May 27, 2005 by mikeman

[Lachesis]

All it does it gets the vertex,texture coordinate and normal data and renders them. Nothing more.

I know, I know. I was just talking about that:

But it's true that if you use vertex shaders you need to replace the whole fixed pipeline(tranformations,texgen,lighting...) too.

 

so it will be much faster and only implement the desired effect.

So using a shader for a single pass wouldn't be faster? But maybe we could compare both.

 

Thank you for your example! I haven't read about predefined functions yet, it seems emulating the fixed functionality is much simpler than I assumed. I'll continue reading, of course; maybe one day I will be able to do these things. Your shader looks like ground fog to me, the plane defined by fog_point and fog_norm certainly is the upper border of the fog. I guess we could hard-code the normal, it's always pointing down directly, so we could just use the corresponding coordinate of the vertex position and do without the scalar product.

 

If you find some time, could you implement the atmospherics? It would certainly take you significantly less time and probably your results would be better than those of most of us.

[mikeman]

Ok... well, I played around a little in my own engine because I want to do atmospherics there too. The problem is not so much with the static ground fog how with how to do the animated mist("steam coming of the ground"). I implemented an idea I had, and it looks interesting:

 

 

All it needs is a quick second pass(no shaders) and a 2D animated texture. The static ground fog is done the same way, you just have a totally white texture instead. When I'm done with Cal3D, I'll try to incoporate it into EL too.

Edited May 28, 2005 by mikeman

[Roja]

hey that looks really nice

Do you need me to make the textures for it or do you already have them?

[Lachesis]

Looks really nice, mikeman! I would really like to see how it looks animated Can you explain how this is done? Only if you find the time and to feed my curiousness.

Edited May 30, 2005 by Lachesis

[mikeman]

Well, it's 2 passes as I said:

 

1)You render the geometry and make it so that in low heights it has white color and black in high heights. I used a 1D gradient texture to do that. You then enable modulative blending and draw a single animated fog plane. That way, pixels that are in low heights get much fog, while pixels that are in high heights get little or no fog.

 

2)Enable additive blending and perform the second pass, which is basically the scene rendered normally(unfogged).

 

This is the technique visually:

 

 

Roja, can you make animated noise textures using a special program or something? If so, then it would be nice. I'm currently using a single noise texture and do a primitive animation based on that, not too ugly but a true animation would look better.

Edited May 30, 2005 by mikeman

[Entropy]

Hmm... we are using a few texture units already (normal texture, clouds shadows, and I think some are used for the deepth buffer shadows as well).

So you might have to do it in two phases (might be slower).

[mikeman]

Hmm... we are using a few texture units already (normal texture, clouds shadows, and I think some are used for the deepth buffer shadows as well).

So you might have to do it in two phases (might be slower).

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Yes, I already said that it needs 2 rendering passes. The first pass is pretty quick though, and after all this effect won't be on all maps. Wherever there's ground fog, that means you can't see water reflections, so you just trade the reflection pass with the additional fog pass.

 

Also, this first pass has the advantage of setting up the z-buffer for the scene. When the normal scene will be rendered(textures+lighting), there will be zero overdraw due to early z-rejection, so that would speed up things too.

Edited May 30, 2005 by mikeman

[Lachesis]

It's amazing what results one can get with such a simple technique. Mikeman, you rule

[Roja]

Hm..no I don't have any programs to make animated noise..i'd just probably have to wing it..just make a few different noise textures and hope they look good animated together :/

[Lachesis]

What shall the animation imitate? Raising steam? What noise function did you use for creating that texture?

[Lachesis]

Idea: let's use a 3D noise function, compute it and use it as a 3D texture? Then we can move the the texture through the plane and create interesting effects

[Nintenduh]

Could ImageMagick's Magick Wand C lib be used to render dynamic atmospherics?

[Lachesis]

How would you use it?

[Nintenduh]

I haven't used their programming interfaces yet, only the command line tools.

 

I'm not exactly sure if it can be done with magickwand. Maybe Magick Core could do the trick better.

 

What I was thinking was adding effects to the existing cloud textures over time. Like a progressive blur and or ripple effect or somthing.