Is CG normalize buggy or is it just me?

General Discussion
1

I’m trying to learn shader programming and it’s not helping when I run into bugs like this:

Normalizing the normal map

float3 normal = normalize( 2*tex2D(tex_0, l_texcoord0) - 1);

This doesn’t produce right normal. The resulting picture is too dark.

float3 normal = 2*tex2D(tex_0, l_texcoord0) - 1);
normal = normalize(normal)

Separating the normalize into its own line produces the correct result.

Has anybody else run into thse problems before? Is there any resources (websites) that detail these gotchas?

2

Actually… it’s not a bug.

tex2D returns a float4, so that means the fourth component is also taken into account
In your second code, you cast the four-component color into a float3 first, so that the result of normalisation will be different as the fourth component is no longer taken into respect.

The fixed version of your first code is:

float3 normal = normalize( 2*tex2D(tex_0, l_texcoord0).rgb - 1);

There are more ways to do it, e.g. using the f3tex2D fixes it too.

3

Ah. Ok. Thanks for the clarification!