How to convert a normal map from tangent space to world space

[zhenhuafan]

I need convert a PNG normal map from tangent space to world space.
First I used getWorldTangentFrame() * normalMap, but the value is not right.
I try to calculate TBN matrix in vertex shader. I realized that I couldn't get the normal and tangent values.

Many thanks if anyone can give any helpful guidance。

The following is the method in Unity that I referenced：
vertex：
float3 worldNormal = UnityObjectToWorldNormal(v.normal);
float3 worldTangent = UnityObjectToWorldDir(v.tangent.xyz);
float3 worldBinormal = cross(worldNormal,worldTangent)*v.tangent.w;
o.T2W0 = float4(worldTangent.x,worldBinormal.x,worldNormal.x, worldPos.x);
o.T2W1 = float4(worldTangent.y,worldBinormal.y,worldNormal.y, worldPos.y);
o.T2W2 = float4(worldTangent.z,worldBinormal.z,worldNormal.z, worldPos.z);

fragment：
float4 Normaltex = tex2D(_BumpMap, i.uv);
float3 tangentNormal = UnpackNormal(Normaltex);
tangentNormal.xy *= 1.0;
tangentNormal.z = sqrt(1.0 - saturate(dot(tangentNormal.xy, tangentNormal.xy)));
float3x3 T2WMatrix = float3x3(i.T2W0.xyz,i.T2W1.xyz,i.T2W2.xyz);
float3 worldNormal = mul(T2WMatrix,tangentNormal);

[show50726]

If your model contains normal and tangent attributes, getWorldTangentFrame() * normalMap should meet your need.
But you said

 I realized that I couldn't get the normal and tangent values.

Does that mean your model does not contain normal and tangent attribute?

[zhenhuafan]

@show50726
My model have normal and tangent attribute. I used the sample demo "sample-lit-cube" in android and the demo “sample_full_pbr.cpp” to verify the convert code ，but the result is different with Unreal.

The normal map is like below ,

and after TransformVector Node (tangents space to world space) in Unreal ,the result is like below

My code in filament fragment is like below, Just can get black result：

        mat3 tangentFromWorld = transpose(getWorldTangentFrame());
        vec3 v = tangentFromWorld * normalMap;
        material.baseColor.rgb = v;

I change the mat file in demo "sample-lit-cube" in android and the demo “sample_full_pbr.cpp” to check result.