Normals and camera/eye direction computations (HLSL)

Björn Näf · 2012-04-12T15:16:09

Hi all! I'm not experienced in vector maths related computations so I need some help here. In the game engine I'm working with (xRay 1.0) I can sample the normal vector of a pixel in a pixel shader like this. float3 N = tex2D(s_normal, texCoord); However it seems the result is not the absolute surface normal vector, but something depending on the camera/eye direction. e.g. when I use the normal vector as color, horizontals are green when the camera points straight forward, but as soon as I turn the camera vertically towards the sky or ground, the color changes to blue or red, respectively, indicating that the "normal" N that I sampled above is somewhat relative to the camera direction rather than absolute. Same thing happens with verticals when turning the camera to the left or right. I have the camera/eye direction vector, so it should be easily possible to get the absolute surface vector with some vector math, but I don't know which formula or HLSL function(s) to use. I tried several combinations of scalar multiplications, divisions, subtractions, and additions, as well as the "dot" and "mul" functions but did not achieve to get a correct result. So, how do I get the absolute surface normal independent from the camera direction out of the above values?

Graphics and GPU Programming Programming

Started by Meltac April 05, 2012 10:45 AM

11 comments, last by Meltac 12 years ago

Meltac

508

Author

April 08, 2012 08:38 PM

Wow, that sounds interesting. I've thought of something like that, however didn't know the ddx/ddy functions. I guess that shall help me out, will take me some trial-and-error cycles though.

Thanks for your help, guys!

kauna

2,925

April 10, 2012 07:47 AM

Can you verify the surface format of the normal texture? There are lots of ways to store inaccurate normals.

Also, I'm not 100% convinced that the matrix you used for the transform is the correct one. Typically the mView matrix is used for world-to-view space transform and what you need is the inverse of that matrix.

Cheers!

Meltac

508

Author

April 12, 2012 03:16 PM

Can you verify the surface format of the normal texture? There are lots of ways to store inaccurate normals.

How would I verify the surface format? I only see what I get when sampling some position, normal, or color value, but what "format" would it have?

Also, I'm not 100% convinced that the matrix you used for the transform is the correct one. Typically the mView matrix is used for world-to-view space transform and what you need is the inverse of that matrix.

I also thought of that. Given the fact that my engine wouldn't provide that inverse matrix, is there a way to compute it out of the mView matrix?

Normals and camera/eye direction computations (HLSL)

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