Help needed: Artist diving into shader programming!

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artquest polycounter lvl 6
Hello all,

I'm starting my journey into shader programming and In many respects I just don't quite know where to begin. I've opened up some HLSL shader files and messed around (with some success) but I feel like I'm blindly poking around in the dark. Does anyone have some good resources for learning HLSL and or GLSL? I've read a lot about the matrices involved (world space/object space/ tangent space) and now I'm wanting to dive in deeper.

I'm familiar with rendering assets in passes and comping them together in photoshop, however I don't fully understand what math is being used to put it all together. For instance, I know I need to use the "screen" blend in PS mode for reflections... but what is the screen mode doing and should I be mimicking that in a shader?

I know light is additive so I need to add the diffuse pass and the specular pass together with the ambient color so:

Diffuse pass = add to ambient/base
Spec pass = add to ambient/base

But what about the rest?

Reflection pass = ?
Shadow pass = ?
Glow/emissive pass = ?

Thanks in advance PCers! :D

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  • Vailias
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    Vailias Polycount Sponsor
    ... Ok I know what I'm doing this weekend. I have a shader artist math tutorial syllabus written up. I just need to get it into video form. Questions like yours keep coming up more and more frequently.

    Very broadly speaking, every "pass" you've mentioned tends to be either additive or multiplicative.

    And really they're not separate passes in shader terms, as a multipass shader takes the previous output as input for it's own routines.

    As far as photoshop math gors, I have a link for that on my home pc. I'll post it here later if someone doesn't beat me to it.
  • artquest
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    artquest polycounter lvl 6
    Vailias wrote: »
    ... Ok I know what I'm doing this weekend. I have a shader artist math tutorial syllabus written up. I just need to get it into video form. Questions like yours keep coming up more and more frequently.

    Very broadly speaking, every "pass" you've mentioned tends to be either additive or multiplicative.

    And really they're not separate passes in shader terms, as a multipass shader takes the previous output as input for it's own routines.

    As far as photoshop math gors, I have a link for that on my home pc. I'll post it here later if someone doesn't beat me to it.

    Oh man I can't wait for that tutorial :D Sounds great. Thank you!!!!
  • glynnsmith
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    glynnsmith polycounter lvl 11
    Vailias wrote: »
    ... Ok I know what I'm doing this weekend. I have a shader artist math tutorial syllabus written up. I just need to get it into video form. Questions like yours keep coming up more and more frequently.

    Very broadly speaking, every "pass" you've mentioned tends to be either additive or multiplicative.

    And really they're not separate passes in shader terms, as a multipass shader takes the previous output as input for it's own routines.

    As far as photoshop math gors, I have a link for that on my home pc. I'll post it here later if someone doesn't beat me to it.

    Yes please.
  • Vailias
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    Vailias Polycount Sponsor
    Ok as for the math behind photoshop blending modes, here's a very thorough coverage
    http://dunnbypaul.net/blends/
  • chronic
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    chronic polycounter lvl 7
    You could pick up one of these great DVD's:
    http://www.cg-academy.net/es_catalog/product_info.php?products_id=64
    http://eat3d.com/shaders_intro

    I made some very basic intro videos here:
    http://www.cgbootcamp.com/tutorials/category/cgfx

    cgfx and hlsl are essentially the same btw.

    reflections are added, you will not be using 'screen mode' in any non-stylized shader.
  • Vailias
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    Vailias Polycount Sponsor
    Never say never. :P
    I'm using a directionaly masked overlay blend to fake SSS in UDK on a current model.
  • equil
    screen is a hack that's necessary to get ok results when working in gamma space. There's no real reason to use this in a shader.

    I think it's a lot easier to think about how material properties work together if you think about them in a physical sense.

    Reflection and Specular is light that bounces right of the surface.
    Diffuse (and Emission) is light that's been absorbed, scattered inside and then partially reemitted from the object.
    Transparency and Translucency is light that is absorbed, scattered and completely reemitted from the object.

    So specular and reflection are technically the same thing, but for a shader programmer, the difference is that the specular is multiplied by the incoming light (nl*shadows), while the reflection isn't.

    emissive is usually added to the ambient light, and thus isn't affected by lighting. the last line in my shaders usually look something like;

    ambient * AO * albedo + reflection * SO + (albedo + specular) * nl * shadows

    albedo is the diffuse map, so is specular occlusion, nl is the dot product between the light and the normal
  • chronic
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    chronic polycounter lvl 7
    screen is dangerous if you are not clamping values to 0-1, you will get negative numbers. clamping limits your shading pipeline and should be avoided.
  • artquest
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    artquest polycounter lvl 6
    equil wrote: »
    screen is a hack that's necessary to get ok results when working in gamma space. There's no real reason to use this in a shader.

    I think it's a lot easier to think about how material properties work together if you think about them in a physical sense.

    Reflection and Specular is light that bounces right of the surface.
    Diffuse (and Emission) is light that's been absorbed, scattered inside and then partially reemitted from the object.
    Transparency and Translucency is light that is absorbed, scattered and completely reemitted from the object.

    So specular and reflection are technically the same thing, but for a shader programmer, the difference is that the specular is multiplied by the incoming light (nl*shadows), while the reflection isn't.

    emissive is usually added to the ambient light, and thus isn't affected by lighting. the last line in my shaders usually look something like;

    ambient * AO * albedo + reflection * SO + (albedo + specular) * nl * shadows

    albedo is the diffuse map, so is specular occlusion, nl is the dot product between the light and the normal

    Wow... so much good information here already and I have a feeling we're just getting started!

    I never knew that screen mode was a hack in gamma space. That makes perfect sense because when compositing in shake or nuke with linear renders you don't use screen for reflections either.
  • artquest
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    artquest polycounter lvl 6
    chronic wrote: »
    screen is dangerous if you are not clamping values to 0-1, you will get negative numbers. clamping limits your shading pipeline and should be avoided.

    Why does clamping limit my shading pipeline and what should be used instead? If I don't clamp(normalize) the dot product of my diffuse calculation then I'll end up with negative numbers as well. What exactly are you referring to when you say I should avoid clamping?

    Edit: oops double post :/
  • chronic
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    chronic polycounter lvl 7
    You need to know when to saturate (clamp to 0-1) and when to use max() to ensure only positive numbers without limiting yourself to the 0-1 range. If something makes sense as 0-1 values (like the return on a dot(N,L) ) you can saturate it but when you start adding up multiple lights you will get values greater than 1 and you want to make sure you keep those intact to allow for tonemapping, bloom, and other post effects later.

    Many of those photoshop blending modes only work correctly with inputs between 0-1, a shader may be carefully written to only have positive values but a screen operation will try to use the inverse of your input by doing a 1-x and give you completely unexpected results.
  • artquest
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    artquest polycounter lvl 6
    chronic wrote: »
    You need to know when to saturate (clamp to 0-1) and when to use max() to ensure only positive numbers without limiting yourself to the 0-1 range. If something makes sense as 0-1 values (like the return on a dot(N,L) ) you can saturate it but when you start adding up multiple lights you will get values greater than 1 and you want to make sure you keep those intact to allow for tonemapping, bloom, and other post effects later.

    Many of those photoshop blending modes only work correctly with inputs between 0-1, a shader may be carefully written to only have positive values but a screen operation will try to use the inverse of your input by doing a 1-x and give you completely unexpected results.


    So how would you handle multiple lights in that situation?

    Another question... When rendering passes I work as much as possible in a linear workflow inside of maya. When programming do I have to worry about linear vs gamma colorspace? How exactly does that come into play? Am I to assume that everything besides file textures are linear?
  • kodde
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    kodde polycounter lvl 12
    artquest> I think HLSL has a simple flag to handle linear from what I've heard. Haven't worked with HLSL myself. When I author my shaders in mental mill I usually handle this manually by x^2.2 on the inputs I want to convert from gamma -> linear, then on the final output you want to convert back to gamma by x^(1/2.2).
  • chronic
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    chronic polycounter lvl 7
    @artquest - are you interested in learning this stuff on a theoretical level or for actually practical use? The discussion is advancing very quickly but it would be much more productive if we could see some of your code and help you along in manageable steps.
    For example, you should really get a shader working with one light, ignoring gamma issues, before worrying about more complex problems.
  • artquest
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    artquest polycounter lvl 6
    chronic wrote: »
    @artquest - are you interested in learning this stuff on a theoretical level or for actually practical use? The discussion is advancing very quickly but it would be much more productive if we could see some of your code and help you along in manageable steps.
    For example, you should really get a shader working with one light, ignoring gamma issues, before worrying about more complex problems.

    I haven't started writing my own shader from scratch yet. I'm working on an expansion pack for a game that happens to need a graphical update. The graphics programmer at our company is booked solid working on another title. So we're having to make due with a programmer who's never done graphics before and myself. We're working together to make this game look the best we can. I felt I could be of more use if I learned as much as I could about shader programming.

    That said, I'm not sure if I can post actual code so I'll just do some examples.

    The code itself is very modular. The diffuse, specular and environment parts are all in their own functions and then called at the end via +=

    so for example

    final color += ambient (Diffuse texture map * ambient color)
    final color += diffuse ( Diffuse texture map* dot(N,L))
    final color += spec ( Diffuse texture map * specular equation)
    * shadows
    return final color;

    I'm having trouble with the specular currently. I can't get it to look right. It's either blown out and too tight or too widespread across the surface. If I mult the spec by dot(nl) inside the specular equation it almost completely disappears because this is happening before it's being added with the color channel instead of after.
  • SpeCter
    I did it like so(this is for one light only, but not hard to change for more):

    float4 Blinn( pixelIn input ) : COLOR
    {
    input.lightDir = normalize( input.lightDir );
    input.viewDir = normalize( input.viewDir );
    input.normal = normalize( input.normal );

    float dotNormalLightDir = dot ( input.lightDir, input.normal );

    float diffuse = saturate(dotNormalLightDir);
    float3 halfVec = normalize(input.viewDir + input.lightDir);
    float dotNormalHalf = dot(halfVec, input.normal);
    float spec = pow(saturate(dotNormalHalf),25);

    return ambientColor + diffuse * diffColor + spec * specColor ;
    }

    I forgot to add the diffuse texture in this one, you have to add that in, sorry for that, just saw that after thinking about that code :poly136:
  • Vailias
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    Vailias Polycount Sponsor
    You are likely working with a blinn/phong specular component.
    Something like
    specColor= tex2d(speccolortexture, inuv);
    h=(cam+l)/2;
    spec =specColor* pow( dot(h,n), specpower);
    

    If it's something like that then the exponent (specpower) is what will control the tightness of the highlight. Values of 1 or lower will be blown out, values over 15 get tight pretty quick.
    If you want to just tone down the brightness, multiply it by something less than 1 before adding it to the diffuse. Also you'll run into blown out areas more often by using the diffuse as the color component to the specular, as anywhere in the hotspot is being effectively multiplied by 2 and taking it out of the 0-1 brightness range. This can be less of an issue if you have a HDR lighting engine, but if not you may want to use either dedicated spec color maps or the 1- the diffuse color if you're stuck with using the single map. That way you'll at least self limit to white (1,1,1) as the maximum possible value for the final pixel color after the add.
  • chronic
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    chronic polycounter lvl 7
    something like this:

    ambient = diffuseTexture * ambientColor
    diffuse = diffuseTexture * dot(N,L) * Shadow
    specular = specularTexture * dot(N,H) * step(0.0, dot(N,L) ) * Shadow

    color = (ambient + diffuse + specular) * ambientOcclusion
    color += reflections

    you can put the calc for diffuse and specular components inside a loop that iterates over your lights

    EDIT: forgot to step the dot(n,l) in the spec, otherwise you darken your spec too much, you just want to take it out of the unlit side, you could use smoothstep() instead to give a soft transition
  • LoTekK
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    LoTekK polycounter lvl 11
    I started my learning by taking apart Ben Cloward's shaders and putting 'em back together again, figuring out what does what and why. They're also very well-documented, which helps a ton:

    www.bencloward.com/resources_shaders.shtml

    After that I grabbed Luiz Kruel's shader production DVD from Eat3D, which in addition to being very well narrated, has a bunch of great examples, and takes you step by step from flat color to lambert to full-on current-gen shader:

    eat3d.com/shaders_intro

    For photoshop blend modes, Vailias' link has lots of good info on what and why. TAO also has a useful list of ready-to-use HLSL translations of the blend functions:

    http://tech-artists.org/wiki/Blending_functions
    I think HLSL has a simple flag to handle linear from what I've heard
    AFAIK, there's a D3D function to do this (D3DSAMP_SRGBTEXTURE), but I haven't seen an equivalent in HLSL. Like kodde, I just use pow(C, gamma) --> pow(C, 1/gamma).

    For specular power, you may want to consider clamping to eg. [0.05, 1.0]. Very low specular power values, at least from my observations, result in artifacts where the specular will spread but then cut off with a hard edge (basically past the light influence).
  • artquest
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    artquest polycounter lvl 6
    chronic wrote: »
    something like this:

    ambient = diffuseTexture * ambientColor
    diffuse = diffuseTexture * dot(N,L) * Shadow
    specular = specularTexture * dot(N,H) * step(0.0, dot(N,L) ) * Shadow

    color = (ambient + diffuse + specular) * ambientOcclusion
    color += reflections

    you can put the calc for diffuse and specular components inside a loop that iterates over your lights

    EDIT: forgot to step the dot(n,l) in the spec, otherwise you darken your spec too much, you just want to take it out of the unlit side, you could use smoothstep() instead to give a soft transition

    Wow that smooth step really did the trick! All the info you guys have posted has been very helpful. My boss is very happy as of this morning too since yesterday our team endured the Eye of Sauron for the game's lack of graphical updates :) Despite being an older game it's starting to look closer to current gen. Thanks everyone for all the help so far.

    Unfortunately we can't do ambient occlusion real time and as much as I would love to bake some textures for it I think we're out of channels in our texture maps. I've tried baking the AO into the diffuse texture but it doesn't give as good of results. But at least it's something.

    Vailias: I removed the diffuse color component from the specular and it helps a lot as well. thx
  • DEElekgolo
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    DEElekgolo polycounter lvl 8
  • artquest
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    artquest polycounter lvl 6
    DEElekgolo wrote: »
    No GLSL bros here?

    I've heard HLSL and GLSL are very similar... is this true?

    Does anyone have any good books to recommend on the subject? We're working in HLSL for our current game but in the near future we plan to use GLSL for our next project.
  • DEElekgolo
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    DEElekgolo polycounter lvl 8
    GLSL is kind of similar to HLSL. It is more similar to C though.
    Only drawback is that it cannot be pre-compiled. It must be stored as plain text through-out.
  • CrazyButcher
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    CrazyButcher polycounter lvl 12
    If you work with GLSL and want for editing purposes quick feedback you can use the cgc.exe (cg compiler) it will accept regular GLSL (even ES). That way you get error messages and even some code that hints to the low-level generation
    www.luxinia.de/index.php/Estrela/Shader (for my own editor I've built myself some shortcuts to offline compilers for cg, glsl or hlsl)
  • Xoliul
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    Xoliul polycounter lvl 8
    I tried to get into GLSL once. I found the whole separate file for pixel and vertex shaders very confusing. But maybe that was just a requirement of Leadwerks? Horrible engine to work with anyway...
  • DEElekgolo
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    DEElekgolo polycounter lvl 8
    In my game I had it parse a single file for pixel and vertex shaders. The shader its self would be separated by doing:
    [Vert]
    //...
    [Frag]
    //...

    That way if I never need to add geometry shaders I can just add [Geometry].

    A sample shader.
    http://pastie.org/2872641
  • equil
    Vailias wrote: »
    specColor= tex2d(speccolortexture, inuv);
    h=(cam+l)/2;
    spec =specColor* pow( dot(h,n), specpower);
    
    any reason why you write the half vector like that? i tried comparing the two methods ( /2 and normalize() ) and the results are pretty different. not sure which one is the correct one, but the /2 version doesn't seem to play well with fresnel.

    halfvector.png
  • LoTekK
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    LoTekK polycounter lvl 11
    I've seen (V+L)/2 being used before, and it seems to work ok when the angle between V and L aren't too large. As they diverge, though, the approximation gets progressively less accurate.

    Afaik, it's not a huge optimisation, and the benefits of normalize(V+L) outweigh any minor costs.
  • Vailias
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    Vailias Polycount Sponsor
    I wrote it that way because it was the main way I've experienced a blinn shader, and it does give you a vector that is half way between the input components.

    and yes the approximation for it being an actual reflection vector breaks down after a while, but should be sufficient for angles up to 90 degrees from the light. In my experience this is used in the specular component only. So if the object you're viewing is between you and your lightsource, you wouldn't get spillover like that anyway, and you wouldn't use it at such a low exponent as to blow out over the whole front surface of the object.

    A simple fresnel term isn't really light direction dependent.. so not sure why you'd use a half vector in the calculations anyway.
  • equil
    Ah, so it's some sort of approximation, thanks for clarifying.

    I guess i wasn't being clear when i mentioned fresnel. I use it to refer to the fresnel equations, or more specifically the fresnel component of the specular highlight. This is definitely light (and view!) dependent, but I'm aware that it sometimes also refers to simple edge brightening/fake rimlighting.

    For reference, specular reflections do get brighter at glancing angles, and this is what the result might look like (increasing roughness from top to bottom, increasing halfvector from right to left). so it definitely makes sense to calculate fresnel with the half vector (since it's a measure of the angle between the light and the viewer).
  • poopipe
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    poopipe polycounter lvl 6
    On the AO thing...

    in the absence of SSAO I've had pretty good success simply adding a precomputed map to the ambient channel - itll react to diffuse light that way which of course it won't if you bake into the diffuse and allows you to add colour rather than just the conventional black&white. Well worth a look if you can afford the extra map
  • Vailias
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    Vailias Polycount Sponsor
    equil: ah right. A more complete fresnel simulation rather than the 1-abs(dot(cam,normal)) type.

    For that a half vector probably wouldn't work as well just due to how its constructed, and the direction it points in space.

    Also the reason you're getting differences between the two versions is the length of the combined vector will not always be 2, and just scaling the resulting vector to length 1 doesn't actually return a vector in between the two original vectors.
    Also I forgot to mention: the reason for a half vector is specifically to compare to the normal of a surface, as its very similar to comparing the reflected camera vector to the light vector when looking for direct specular reflection.

    Remember there is a big difference between a vector halfway between two others, and half the angle between two vectors. So for things like the Theta term in Schlick's reflectance model, a half vector will not generate proper output.
  • CrazyButcher
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    CrazyButcher polycounter lvl 12
    DEElekgolo wrote: »
    In my game I had it parse a single file for pixel and vertex shaders. The shader its self would be separated by doing:
    A sample shader.
    http://pastie.org/2872641

    You can also use the regular c preprocessor for this. GLSL program is built from multiple strings, first string could be "#version 120", second string, "#define _VERTEX_", and then the program string, which separates sections trhough #ifdef _VERTEX_ #endif. Although it does look less nice as custom tags.
  • artquest
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    artquest polycounter lvl 6
    poopipe wrote: »
    On the AO thing...

    in the absence of SSAO I've had pretty good success simply adding a precomputed map to the ambient channel - itll react to diffuse light that way which of course it won't if you bake into the diffuse and allows you to add colour rather than just the conventional black&white. Well worth a look if you can afford the extra map

    Aight so thanksgiving week has been crazy but now things are slowing down a bit and I can get back into shader stuff. :)

    Since we're not 64 bit we don't have the ram to add another texture map for every ship. We're currently limited to diffuse, team color, spec, self illumination, reflection, and a bloom map for the full screen glow post process.

    I figure I'm just going to have to live without ambient occlusion but maybe there's some whacky creative hack that could work. Thoughts?
  • SpeCter
    artquest wrote: »
    Aight so thanksgiving week has been crazy but now things are slowing down a bit and I can get back into shader stuff. :)

    Since we're not 64 bit we don't have the ram to add another texture map for every ship. We're currently limited to diffuse, team color, spec, self illumination, reflection, and a bloom map for the full screen glow post process.

    I figure I'm just going to have to live without ambient occlusion but maybe there's some whacky creative hack that could work. Thoughts?

    Why don´t you just blend predefined colors into the diffuse for team color instead of using a whole map?
  • LoTekK
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    LoTekK polycounter lvl 11
    artquest wrote: »
    We're currently limited to diffuse, team color, spec, self illumination, reflection, and a bloom map for the full screen glow post process.

    Elaborating on Specter's point, as long as you're not talking about fancy multiple colors per team, you can multiply a flat color on top of the diffuse, via a mask. This way your team color map will go from a full color RGB map to a single channel (ie, grayscale). Depending on your other maps, you can either stick this in an alpha channel, or combine other grayscale maps into a single RGB image.

    For example, depending on how you're using your self illum and bloom masks, you could combine:
    Team Color: RED
    Self Illum: GREEN
    Bloom Map: BLUE

    Which effectively saves you two texture sampler slots.
  • artquest
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    artquest polycounter lvl 6
    LoTekK wrote: »
    Elaborating on Specter's point, as long as you're not talking about fancy multiple colors per team, you can multiply a flat color on top of the diffuse, via a mask. This way your team color map will go from a full color RGB map to a single channel (ie, grayscale). Depending on your other maps, you can either stick this in an alpha channel, or combine other grayscale maps into a single RGB image.

    For example, depending on how you're using your self illum and bloom masks, you could combine:
    Team Color: RED
    Self Illum: GREEN
    Bloom Map: BLUE

    Which effectively saves you two texture sampler slots.

    Ops, should have been more clear. Our team color is a mask in the alpha of the diffuse. The second texture contains specular in the red channel, self illum in the green channel, reflection in the blue channel, and bloom masks are in the alpha of the second texture. We use dxt 5 for almost everything and dxt5nm for normal maps.

    Memory is getting to be a concern with how many assets we have in the game. We would really love to breathe some new life into the graphics but we're going to have to be really careful about what we do since we don't want to cripple performance. It is just an expansion after all(for a 3 year old game).
  • equil
    Artquest, have you considered baking ao to vertex colors?
    Vailias wrote:
    Also I forgot to mention: the reason for a half vector is specifically to compare to the normal of a surface, as its very similar to comparing the reflected camera vector to the light vector when looking for direct specular reflection.

    Remember there is a big difference between a vector halfway between two others, and half the angle between two vectors. So for things like the Theta term in Schlick's reflectance model, a half vector will not generate proper output.

    The reason for a half vector is that a reflection vector breaks down on any surface that doesn't have an optically flat microstructure. The derivation for it is pretty boring (it's more or less a solution to a filtering issue). Leaving that can of worms aside, I guess your argument was that you shouldn't compare half vectors to anything but surface normals?

    ...Which isn't really accurate. Comparing the half vector and the light or view vector is exactly what you want. In the fresnel equations θ represents the angle between the light and surface direction (In a model applying microfacet theory like blinn etc, this is measured by H). Also in Schlick's own paper, he himself specifically uses H.V as input for his fresnel equation. I'm not sure what you think would be better.
  • artquest
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    artquest polycounter lvl 6
    equil wrote: »
    Artquest, have you considered baking ao to vertex colors?



    The reason for a half vector is that a reflection vector breaks down on any surface that doesn't have an optically flat microstructure. The derivation for it is pretty boring (it's more or less a solution to a filtering issue). Leaving that can of worms aside, I guess your argument was that you shouldn't compare half vectors to anything but surface normals?

    ...Which isn't really accurate. Comparing the half vector and the light or view vector is exactly what you want. In the fresnel equations θ represents the angle between the light and surface direction (In a model applying microfacet theory like blinn etc, this is measured by H). Also in Schlick's own paper, he himself specifically uses H.V as input for his fresnel equation. I'm not sure what you think would be better.


    I haven't considered baking the AO to vertex colors. I wonder if our game supports that...

    I just had another idea though. If my normal map is DXT5nm format it's only using the red and the alpha channel so I should simply be able to manually recreate the swizzling that format does and save it as a regular DXT5. This leaves me with the green and blue channels free. Perhaps I could place a baked amb occlusion there?
  • artquest
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    artquest polycounter lvl 6
    Alright, I'm resurrecting this thread ** casts NECRO on thread ** and calling upon you awesome peeps for some more help!

    I've downloaded nvidia's fx composer and am writing a shader from scratch in it. I'm quite enjoying the process so far. But now I've hit a bit of a road block. It seems that if I use:

    dot(Light, Normal)

    this will only give me an interpolation between white and black for my lighting. Thats great if you want to multiply it over the top of your diffuse map texture. But with this method the lightest pixel at any point on the model is the value of your hand painted texture.

    So how do I create a shader that behaves similiar to in maya where if you increase the light intensity (with the light color set to white) the entire lit area becomes lighter than the diffuse texture value?

    Another part of this that i'd like to look into is being able to create a stylized look by having the "dark" or unlit areas be a color of my choosing that instead of being multiplied over the diffuse texture would blend(interpolate) into the solid color.

    So from my description I guess I'd need to split my diffuse shading into 2 parts? I.e. I start with my object (ambient color to show the mid range of diffuse texture), then interpolating to the the "dark" or unlit/solid color side of the object and then an additive process to brighten the object's lit side.


    Thanks in advance all you shader wizards!



    EDIT: I whipped this up real quick in PS to explain what I want to achieve. (I know the colors are ugly! but it's so you can see the effect lol)

    ShaderLookDev2.jpg
  • kodde
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    kodde polycounter lvl 12
    artquest wrote: »
    Alright, I'm resurrecting this thread ** casts NECRO on thread ** and calling upon you awesome peeps for some more help!

    I've downloaded nvidia's fx composer and am writing a shader from scratch in it. I'm quite enjoying the process so far. But now I've hit a bit of a road block. It seems that if I use:

    dot(Light, Normal)

    this will only give me an interpolation between white and black for my lighting. Thats great if you want to multiply it over the top of your diffuse map texture. But with this method the lightest pixel at any point on the model is the value of your hand painted texture.

    So how do I create a shader that behaves similiar to in maya where if you increase the light intensity (with the light color set to white) the entire lit area becomes lighter than the diffuse texture value?

    Another part of this that i'd like to look into is being able to create a stylized look by having the "dark" or unlit areas be a color of my choosing that instead of being multiplied over the diffuse texture would blend(interpolate) into the solid color.

    So from my description I guess I'd need to split my diffuse shading into 2 parts? I.e. I start with my object (ambient color to show the mid range of diffuse texture), then interpolating to the the "dark" or unlit/solid color side of the object and then an additive process to brighten the object's lit side.


    Thanks in advance all you shader wizards!



    EDIT: I whipped this up real quick in PS to explain what I want to achieve. (I know the colors are ugly! but it's so you can see the effect lol)

    ShaderLookDev2.jpg

    Not exactly sure I understand what you want to achieve. But from what I understand you want the resulting color to be "blown out", i.e. go brighter than the diffuse-texture color right? Sounds like default behavior to me. I mean, the equation is diffuse light * diffuse texture. So by having a light source which is above 1.0 value you would get a resulting color which is lighter than the diffuse texture right?

    For example, let's say the diffuse texture is 0.5,0.5,0.5 and the light is a bright white light of 1.5,1.5,1.5. That would result in the final color of 0.75,0.75,0.75 which is brighter than our diffuse texture.

    Maybe you don't have thought about having the light final color going above 1.0? You could incorporate an "intensity" for the light which is multiplied by the light color?

    For playing around with stylized look you are talking about I'd look into using ramp textures to define this. It's a nice and easy way to play around with it imo. I've only ever created this with node based shader editors so I'm not sure how to code it. But you should quite easily be able to find info on it. I know for instance that the TF2 shading whitepaper has some info on this, they use this technique for their shading.
  • artquest
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    artquest polycounter lvl 6
    kodde wrote: »
    Not exactly sure I understand what you want to achieve. But from what I understand you want the resulting color to be "blown out", i.e. go brighter than the diffuse-texture color right? Sounds like default behavior to me. I mean, the equation is diffuse light * diffuse texture. So by having a light source which is above 1.0 value you would get a resulting color which is lighter than the diffuse texture right?

    For example, let's say the diffuse texture is 0.5,0.5,0.5 and the light is a bright white light of 1.5,1.5,1.5. That would result in the final color of 0.75,0.75,0.75 which is brighter than our diffuse texture.

    Maybe you don't have thought about having the light final color going above 1.0? You could incorporate an "intensity" for the light which is multiplied by the light color?

    For playing around with stylized look you are talking about I'd look into using ramp textures to define this. It's a nice and easy way to play around with it imo. I've only ever created this with node based shader editors so I'm not sure how to code it. But you should quite easily be able to find info on it. I know for instance that the TF2 shading whitepaper has some info on this, they use this technique for their shading.

    hrm... so I guess inside nvidia fx composer it's just that my light color wont allow me to to above 1. I'll have to add an intensity multiplier like you suggested. Thanks!

    However I'd still like to look into doing the diffuse calculation in an additive manner. Because my end goal is to create a shader that takes into account color temperature in regard to the light source.

    diffuse texture * diffuse lighting gives you a result that is unnatural. I want to create a falloff effect based on the color of my light. As light gets less intense it shifts in hue and saturation as well as value. The brighter the light reflected, the less saturated the color, the darker the shadowed area is the more saturated the light color is. (my example ended up looking a little like skin but it's not supposed to be :P just a sphere painted cream color with a yellow light shining on it.)

    Shader.jpg
  • haiddasalami
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    haiddasalami polycounter lvl 7
    That just looks like a half lambert and maybe just saturate the ambient more? Just a thought.
  • artquest
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    artquest polycounter lvl 6
    That just looks like a half lambert and maybe just saturate the ambient more? Just a thought.

    My example isn't quite an exact look... it's more the concept that I would like to be able to write into my shader. I'm interested in creating a shader that will handle this dynamically based on the light. Offsetting the hue and saturation automatically based on the light color.
  • kodde
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    kodde polycounter lvl 12
    artquest> You can easily get that result with the ramp suggestion I spoke of in my earlier post.
  • artquest
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    artquest polycounter lvl 6
    kodde wrote: »
    artquest> You can easily get that result with the ramp suggestion I spoke of in my earlier post.

    Thanks! So once I set up the ramp, does anyone know how to plug those values into the diffuse lighting calculation?

    I haven't had time to look over the valve link. But I will for sure do that soon :)
  • haiddasalami
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    haiddasalami polycounter lvl 7
    I know Xoliul has something like this:

    ShadedHueAnim.gif

    Link to Xoliul Shader Think you want the core one.
  • kodde
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    kodde polycounter lvl 12
    The basic theory is you take the result from the diffuse light and feed that into a texture lookup's U or V coordinate (depending on if you use a lying or standing ramp).

    That way, if the diffuse calculation gives a a light color, it will sample in one end of the ramp, and if it's a dark color it would sample in the other end of the ramp.

    Sort of like "filtering" the diffuse results through a texture.
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