why view direction `eye_normal` starts from eye?

[cedarz]

https://github.com/CaffeineViking/vkhr/blob/master/share/shaders/strands/strand.frag#L45

vec3 eye_normal = normalize(fs_in.position.xyz - camera.position);

eye_normal is as input for kajiya_kay, and the result specular highlights have some difference.

if using vec3 eye_normal = normalize(fs_in.position.xyz - camera.position);

else if use 'vec3 eye_normal = -normalize(fs_in.position.xyz - camera.position);`

But the eye_nomal of other implementations I find is vec3 eye_normal = normalize(fs_in.position.xyz - camera.position); from pos (of model) to eye, can you give me some hints?

PS: I disable occlusion and shadow when capturing the screenshots