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cozzie

DX11 Specular normalization (blinn phong)

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Hi all,

I've been puzzling with my specular highlights, trying to add specular normalization.
Basically applying the theory from this article: https://seblagarde.wordpress.com/tag/specular/

float normFactor = (power + 2.0f) / ( 4.0f * PI * ( 2.0f - (2.0f * (-power / 2.0f) ) ) );

When I apply this in my shader like this, I get basically no more specular at all:

// specular Blinn-phong
float power = pLightSetup.mat.SpecPower;
float normFactor = (power + 2.0f) / ( 4.0f * PI * ( 2.0f - (2.0f * (-power / 2.0f) ) ) );

float tIntensity = pLightSetup.mat.SpecIntensity;

// Blinn-phong specular
float3 HalfWay = normalize(toEye + -dirLight.Direction);
NdotH = saturate(dot(HalfWay, pLightSetup.Normal));
specular = dirLight.ColorIntensity.rgb * pow(NdotH, power) * tIntensity;
specular *= normFactor;

Result:

2019-06-10-specular-norm.jpg

And this is the result if I just comment out the *= normFactor:

2019-06-10-specular-nonorm.jpg

I also played around increasing the specular intensity + using normalization, this is with intensity 40.0 and normalization:

2019-06-10-specular-norm-intx40.jpg

Top row = specular power 16, left to right: intensity 0.1, 0.2, 0.4, 0.7, 1.0
Bottom row = intensity 1.0, left to right: power 10, 25, 50, 100, 300.
(in the last screenshot the intensities are multiplied by 40.0f).

Question:
The goal of the normalization is to make the sharper (higher power) highlights appear sharp/ strong, and the lower power highlights, be more 'vague'/ rough.

Any thoughts on what I might be doing wrong?
All input is appreciated.

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2 hours ago, cozzie said:

float normFactor = (power + 2.0f) / ( 4.0f * PI * ( 2.0f - (2.0f * (-power / 2.0f) ) ) );

Shouldn't this be:

(power + 2.0f)/(4.0f*PI*( 2.0f-exp2(-power / 2.0f)))

These equations mention exp2 while you just multiply there, which has quite different effect...

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@noizex you're a life saver, that was it! It works now, screenshot below.
I misread the formula, that few pixels that this part of the formula was 'higher' 😎

2019-06-11-specular-norm-fixed.jpg

I did it by breaking up the formula into pieces, works best for me (I can now combine them again).
Also since this is material dependent and not dependent on the lightsource are resulting light, it's something I can calculate offline to save quite some cycles.

float power = pLightSetup.mat.SpecPower;

float a = power + 2.0f;
float b1 = 4.0f * PI;
float b2 = -power / 2.0f;
float b3 = exp2(b2);

float b = b1 * (2.0f - b3);
float normFactor = a / b;

 

Edited by cozzie

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