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normal mapping messing up cos angle ?

2 posts in this topic

I'm having problems with the lighting in my shader when using normal mapping instead of just passing the normals.
Better look at the screenshots (angles are all correct without normal mapping, directional light source (0, 0, 1))

without normal mapping front:

with normal mapping front:

with normal mapping back:

As you can see here also on the specular only picture (from the back of the cube):

The NdotL product here is wrong as it can not possibly be > 0.0f.
Everything except the front face of the cube should essentially be lit and the rest completely black as it is the case when not using normal mapping.
All sides of the cube seem to have a final normal that does make the side faces lit a little bit except the face in the back, which makes the whole image look odd.
Why is this ? Is there some angle check that I'm missing ?

Here's how I calculate the tangent/bitangent in my application:
// Calculate bitangent
for(int i = 0; i < 24; i++)
XMVECTOR normal = XMVectorSet(this->texturedNormalVertices[i].normal.x,
XMVECTOR tangent = XMVector3Cross(normal, forward);
XMFLOAT4 tang;
XMStoreFloat4(&tang, tangent);
float magnitude = sqrt(tang.x * tang.x + tang.y * tang.y + tang.z * tang.z);
if( magnitude == 0 )
tangent = XMVector3Cross(normal, up);
XMVECTOR biTangent = XMVector3Cross(normal, tangent);
// Calculate tangent
XMVECTOR dot = XMVector3Dot(XMVector3Cross(normal, tangent), biTangent);
if (XMVectorGetX(dot) < 0.0f)
tangent = tangent * -1.0f;
XMStoreFloat3(&this->texturedNormalVertices[i].tangent, tangent);
XMStoreFloat3(&this->texturedNormalVertices[i].biTangent, biTangent);

And here's the shader code:
[b]VS part:[/b]
// Calculate View-space Tangent-BiTangent-Normal matrix
output.TBN[0] = mul(input.Tangent, (float3x3)WorldView);
output.TBN[1] = mul(input.BiTangent, (float3x3)WorldView);
output.TBN[2] = mul(input.Normal, (float3x3)WorldView);

[b]PS part:[/b]
// Normal Mapping
float4 NormalMapped = (2.0f * NormalMap.Sample(LinearSampler, input.UV)) - 1.0f;
NormalMapped = normalize(NormalMapped);
float3 N = normalize(mul(NormalMapped.xyz, (float3x3)input.TBN));

[b]the BRDF:[/b]
float4 Gaussian(in float3 Normal, in float3 LightDir,
in float3 ViewDir, in float SpecularPower,
in float3 SpecularAlbedo, in float SpecularIntensity)
const float kPI = 3.1415926536f;

float3 N = normalize(Normal);
float3 L = normalize(LightDir);
float3 V = normalize(ViewDir);
float3 H = normalize(-L - V);

float4 Lr = float4(0, 0, 0, 1);
float4 Ls = float4(0, 0, 0, 1);

// Incident irradiance
float4 Ei = _LightColor * _LightIntensity;

// Lambert
float NdotL = saturate(dot(N, -L));
float kd = NdotL; // diffuse constant
Lr = (kd / PI) * Ei; // outgoing radiance

// Gaussian Specular [Mittring12]
float normalizationFactor = 0.17287429f + 0.01388682f * SpecularPower; // approximation by Krzysztof Narkowicz
float NdotH = saturate(dot(N, H));
float Threshold = 0.04f;
float cosAngle = pow(Threshold, 1 / SpecularPower);
float normAngle = (NdotH - 1) / (cosAngle - 1);

float Specular = exp(-normAngle * normAngle) * NdotL;
Specular *= normalizationFactor;

Ls = float4(Specular, Specular, Specular, 1.0f);
Ls.rgb *= SpecularAlbedo * SpecularIntensity;

return float4(Lr + Ls);
[/CODE] Edited by lipsryme

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Have you tried a simpler NdotL lighting model? Have you verified that all your calculations done in the view space?
Have checked that your TBN matrix is calculated correctly?


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Ah... I knew the brdf would distract people [img]http://public.gamedev.net//public/style_emoticons/default/tongue.png[/img]
It shouldn't be wrong. Plus I've tested it with just a saturate(dot(N, -L)) as output with the same result.
If I don't use the TBN matrix and just use the normals everything works as intended. But once I combine that with the input from the normal map and the TBN matrix it goes wrong.

Well how much more is there to it than just this?

// Calculate View-space Tangent-BiTangent-Normal matrix

output.TBN[0] = mul(input.Tangent, (float3x3)WorldView);
output.TBN[1] = mul(input.BiTangent, (float3x3)WorldView);
output.TBN[2] = mul(input.Normal, (float3x3)WorldView);


I'm just taking the rotational part of the worldview matrix (yes I've tried just world space lighting -> same issue) and multiplying that with the tangent, bitangent and normal for this specific vertex. Basically just what I do in my code snippets up there.

[b]update: [/b]so pix is telling me I've got an NdotL of 0.436 when looking at the side of the cube.
LightDirection in view space = (-0.997, -0.002, 0.074)
Normal in view space = (-0.368, -0.055, 0.928)

The Light Direction is most definitely right so it's obviously that the problem seems to be the normal.
The thing though is like I said it's just wrong when using the TBN. So either the tangent/bitangent is wrong or something I'm doing in the shader code.

[b]update2: [/b] looking at the vertex shader I can see the following:
input.Tangent = (0, 1, 0)
input.BiTangent = (0, 0, -1)
input.Normal = (-1, 0, 0)

TBN after mul with WorldView matrix:
(0, 0.250, 0.007)
(0.249, 0, -0.018)
(-0.018, 0.007, -0.249)

[b]update3: [/b]I just tried normal mapping with the same textures in FXcomposer. Funny thing is the result is the same.
But I don't really get it. I don't see how this is realistic. Having almost half the light that shines onto the front face also on the side faces and the back face of the cube being completely black. Edited by lipsryme

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