Hi all,

now that I’ve managed to get my normal mapping working, I’m at the point of making a “clean” implementation.

Would you know if there’s a general consensus on the following 2 things:

1. Normal mapping in world space vs tangent space (multiply T, B and N in PS versus converting light direction to tangent space in VS, pass to PS)

2. Provide tangents and bitangents to the GPU in vtxbuffer versus calculating in the shader 

What I’ve learned so far is that performing it in tangentspace is preferred (convert light dir in VS and pass that to the PS), combined with calculating the bitangent (and perhaps also tangent) in the VS, per vertex.

I know the answer could be profiling, but that’s not something I’m doing at this stage. Just want to decide my 1st approach.

Any input is appreciated.

1. Converting light directions to tangent space in the VS isn't practical for handling arbitrary numbers of lights, since you're very limited in the number of interpolants that you can pass between the VS and PS (this is especially true from a performance POV). There's also any number of other things that might happen in the PS that need the final surface normal, such as cubemap reflections or SH ambient lighting. I would just convert the normalmap normal to world space and work from there. It will make your code cleaner, and you'll be in a better spot if you start adding more advanced techniques.
2. To compute per-vertex tangents you really need more global info about the triangle and its neighbors. This is why it's very common to compute tangents in an offline pass during mesh import/processing. It is possible to use pixel shader derivatives to compute a tangent frame on-the-fly, but you may run into issues if the derivatives are inaccurate.

Thanks, this helps. I’ll go for providing normal and tangent through the vtx buffer (so calculated offline) and just calculatie bitangent in the VS with 1 cross product. I’ll do the normal mapping in world space (pass TBN in worldspace to the PS).

@d07RiV thanks for digging it up

Articles and papers are not very clear/ consistent on if/ when to use the sign for the bitangent. My use-case is that I provide the normal and tangent to the GPU (via vtxbuffer), and then in the VS I calculate bitangent with a simple cross:

	if(gPerMaterial.Material.UseNormalMap == 1)
	{
		float3 tBitangent = cross(vin.Tangent, vin.NormalL);
		
		// TBN for normal mapping
		vout.TangentW	= mul(vin.Tangent, (float3x3)gPerObject.WorldInvTranspose);
		vout.BitangentW	= mul(tBitangent, (float3x3)gPerObject.WorldInvTranspose);
		vout.NormalW	= mul(vin.NormalL, (float3x3)gPerObject.WorldInvTranspose);
	}
	else 
		vout.NormalW = mul(vin.NormalL, (float3x3)gPerObject.WorldInvTranspose);

Now the question is, is this the way to go (independent on mirrored/flipped situations), or do I have to do something like this:

- check if untransformed normal.z > 0 or < 0, if > sign = +, if < sign = -
- apply that sign to all 3 transformed vectors? (T, B and N) or before transforming?

Note that the vectors are float3's, so no W component for storing anything
Note 2: this is the original vertex normal, no normapmap involved yet