Method sample_tangent_normal

tools/bloom-reference/src/main.rs:327–343

Sample a tangent-space normal from the normal texture, in [-1,1]³. Returns (0,0,1) (i.e. "no perturbation") when the material has no normal map so callers can uniformly apply the TBN transform without a special case.

(&self, material: &Material, uv: Vec2)

    /// material has no normal map so callers can uniformly apply the
    /// TBN transform without a special case.
    fn sample_tangent_normal(&self, material: &Material, uv: Vec2) -> Vec3 {
        let tex_idx = match material.normal_texture {
            Some(i) => i as usize,
            None => return Vec3::new(0.0, 0.0, 1.0),
        };
        let (r, g, b) = match self.sample_texture_linear(tex_idx, uv) {
            Some(c) => c,
            None => return Vec3::new(0.0, 0.0, 1.0),
        };
        // glTF stores normal maps with Y-up in tangent space: the
        // sampled RGB maps linearly from [0,1] to [-1,1]. Apply the
        // material's normal_scale to X/Y (Z is derived).
        let nx = (r * 2.0 - 1.0) * material.normal_scale;
        let ny = (g * 2.0 - 1.0) * material.normal_scale;
        let nz = b * 2.0 - 1.0;
        Vec3::new(nx, ny, nz).normalize_or_zero()
    }

    /// Bilinear linear-space texture sample (no sRGB decode). Used
    /// for MR / normal / occlusion textures per glTF spec.