Why do we use only specular dds for IBL?

SilverBullet · February 19, 2019, 8:57am

How does Babylon handle the diffuse irradiance?

Deltakosh · February 19, 2019, 3:42pm

Hello!
Does that help: Master Physically Based Rendering (PBR) - Babylon.js Documentation ?

SilverBullet · February 20, 2019, 2:05am

Hi Deltakosh,
Thanks for the link. I am still confused somehow. As far as I know, we could use a convoluted texture to model the irradiance (diffuse) part. So how can we eliminate this one in Babylon? Is there a white paper or something which explains this technique in detail?

Deltakosh · February 20, 2019, 4:36pm

If you read shaders then you can go there:

github.com

BabylonJS/Babylon.js/blob/master/src/Shaders/pbr.fragment.fx

#if defined(BUMP) || !defined(NORMAL) || defined(FORCENORMALFORWARD) || defined(SPECULARAA) || defined(CLEARCOAT_BUMP) || defined(ANISOTROPIC)
#extension GL_OES_standard_derivatives : enable
#endif

#ifdef LODBASEDMICROSFURACE
#extension GL_EXT_shader_texture_lod : enable
#endif

#ifdef LOGARITHMICDEPTH
#extension GL_EXT_frag_depth : enable
#endif

precision highp float;

#include<__decl__pbrFragment>

uniform vec4 vEyePosition;
uniform vec3 vAmbientColor;
uniform vec4 vCameraInfos;

This file has been truncated. show original

But else we implement the Disney BRDF.

Not sure though to get your question You want to eliminate the irradiance?

SilverBullet · February 21, 2019, 1:13am

No I don’t want to eliminate the irradiance. I just wonder how we can calculate the diffuse without an irradiance map?

SilverBullet · February 21, 2019, 2:03am

Ah! I vaguely remember that Babylon use Spherical Harmonics to handle the irradiance instead of irradiance map. I will dig more in the implementation detail.

SilverBullet · February 21, 2019, 2:19am

Here I see Irradiance Jones.

github.com

BabylonJS/Babylon.js/blob/0d5a115ffa1eabde8d330b4068e3bcf49810ad24/src/Shaders/ShadersInclude/harmonicsFunctions.fx#L18


uniform vec3 vSphericalXY;

uniform vec3 vSphericalYZ;

uniform vec3 vSphericalZX;



vec3 quaternionVectorRotation_ScaledSqrtTwo(vec4 Q, vec3 V){

    vec3 T = cross(Q.xyz, V);

    T += Q.www * V;

    return cross(Q.xyz, T) + V;

}



vec3 environmentIrradianceJones(vec3 normal)

{

    // Fast method for evaluating a fixed spherical harmonics function on the sphere (e.g. irradiance or radiance).

    // Cost: 24 scalar operations on modern GPU "scalar" shader core, or 8 multiply-adds of 3D vectors:

    // "Function Cost 24	24x mad"



    // Note: the lower operation count compared to other methods (e.g. Sloan) is by further

    // taking advantage of the input 'normal' being normalised, which affords some further algebraic simplification.

    // Namely, the SH coefficients are first converted to spherical polynomial (SP) basis, then 

    // a substitution is performed using Z^2 = (1 - X^2 - Y^2).

How ever I have trouble to find the original white paper. Could you please help me if you know where I can find the original paper?

Many thanks!

Deltakosh · February 21, 2019, 4:44pm

Pinging @sebavan who wrote the shader

sebavan · February 21, 2019, 4:59pm

No paper on this one, a friend of mine created it and I blindly trusted and reused it knowing the sh were giving the same results for a bit more compute if I remember well.

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Why do we use only specular dds for IBL?

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