Switch normal mapping to shader flag instead of shaderdef

[NotAFile]

Objective

• Make the normal mapping functionality reusable across shaders by making it a flag, just like the other textures
• Allow using your own texture locations instead of the hardcoded pbr bindings, like with other textures.

Solution

• The #ifdef calls are replaced by if statements (does not measurably impact performance, uniform branches are ~free on reasonably modern hardware)
• The texture sampling is moved out of apply_normal_mapping into the shader main to match the other textures
• All examples I could find were checked to make sure they still render identically

cc @superdump

---

Changelog

Changed

• The PBR normal mapping functions can now work on custom normal map data

Migration Guide

If you have custom shaders that use apply_normal_mapping, prepare_world_normal, or #define STANDARDMATERIAL_NORMAL_MAP, they must be adjusted as follows:

Pass the material flags directly instead of only checking for double sidedness

pbr_input.world_normal = prepare_world_normal(
    in.world_normal,
    in.is_front,
    material.flags,
);

replace #ifdef STANDARDMATERIAL_NORMAL_MAP with flag checks

if (material.flags & STANDARD_MATERIAL_FLAGS_NORMAL_MAP_TEXTURE_BIT) != 0u {
    // your code here
}

When normal mapping is used, sample the texture yourself.

if (material.flags & STANDARD_MATERIAL_FLAGS_NORMAL_MAP_TEXTURE_BIT) != 0u {
    // NOTE: Do NOT normalize this value before applying normal mapping
    // http://www.mikktspace.com/
    let tangent_normal = textureSample(normal_map_texture, normal_map_sampler, in.uv).rgb;
    N = apply_normal_mapping(
        material.flags,
        pbr_input.world_normal,
        in.world_tangent,
        tangent_normal,
    );
}

If you are not using a normal map, simply replace the call to apply_normal_mapping with normalize

pbr_input.N = normalize(pbr_input.world_normal);

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[nicopap]

I think this is an improvement. The current apply_normal_mapping function is odd and requires a lot of #ifdef conditionals at the function call site. Why? Well, mostly to avoid the user a normalize(pbr_input.world_normal). This reduces complexity a fair bit.

[NotAFile]

Oops sorry for that nicopap. I should resolve the conflicts first.

[NotAFile]

I feel like this one is behind enough at this point that the conflicts are bigger than the actual work. I'd probably put this one up for adoption or turn it into an issue again to help the rendering backlog.