Method sample_importance

tools/bloom-reference/src/main.rs:1636–1650

Draw a direction from the env's luminance distribution along with the per-solid-angle PDF of that choice. The PDF is what MIS needs when weighting this sample against a BRDF sample.

(&self, rng: &mut Rng)

    /// with the per-solid-angle PDF of that choice. The PDF is what
    /// MIS needs when weighting this sample against a BRDF sample.
    fn sample_importance(&self, rng: &mut Rng) -> (Vec3, Vec3, f32) {
        let (x, y, pixel_p) = self
            .distribution
            .sample_pixel(rng.next_f32(), rng.next_f32());
        let (direction, sin_theta) = self.pixel_to_direction(x, y);
        let radiance = self.sample(direction);
        // Convert pixel probability → solid-angle PDF.
        //   pdf_omega = pixel_p / (omega_per_pixel)
        //   omega_per_pixel = (2π/W)(π/H)·sin(θ)
        let omega_per_pixel = (2.0 * std::f32::consts::PI / self.width as f32)
            * (std::f32::consts::PI / self.height as f32)
            * sin_theta.max(1e-6);
        let pdf = pixel_p / omega_per_pixel;
        (direction, radiance, pdf)
    }

    /// PDF (per solid angle) of the env distribution for a given
    /// direction. Evaluates the pixel the direction maps to and