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Multiple importance sampling is now basically working.

Browse Source 
Intersecting rectangular lights still isn't implemented, and there
are likely bugs in the MIS implementation, but it's more-or-less
working!
This commit is contained in:
Nathan Vegdahl 2017-08-16 20:04:06 -07:00
parent 462977bd4d
commit 5a03a46ac7
6 changed files with 79 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
src/light/rectangle_light.rs
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@ -192,7 +192,8 @@ impl<'a> Surface for RectangleLight<'a> {
space: &[Matrix4x4],
) {
let _ = (accel_rays, wrays, isects, shader, space);
unimplemented!()
// TODO
// unimplemented!()
}
}

20
src/light/sphere_light.rs
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@ -15,6 +15,11 @@ use surface::{Surface, SurfaceIntersection, SurfaceIntersectionData};
use super::SurfaceLight;
// TODO: use proper error bounds for sample generation to avoid self-shadowing
// instead of these fudge factors.
const SAMPLE_RADIUS_EXPAND_FACTOR: f32 = 1.001;
const SAMPLE_RADIUS_SHRINK_FACTOR: f32 = 0.99;
// TODO: handle case where radius = 0.0.
#[derive(Copy, Clone, Debug)]
@ -140,14 +145,23 @@ impl<'a> SurfaceLight for SphereLight<'a> {
);
// Calculate the final values and return everything.
let shadow_vec = ((x * sample.x()) + (y * sample.y()) + (z * sample.z())) *
space.inverse();
let shadow_vec = {
let sample_vec = (x * sample.x()) + (y * sample.y()) + (z * sample.z());
let sample_point = (arr + sample_vec).into_vector().normalized() * radius as f32;
let adjusted_sample_point = sample_point * SAMPLE_RADIUS_EXPAND_FACTOR;
(adjusted_sample_point.into_point() - arr) * space.inverse()
};
let pdf = uniform_sample_cone_pdf(cos_theta_max);
let spectral_sample = (col * surface_area_inv as f32).to_spectral_sample(wavelength);
return (spectral_sample, shadow_vec, pdf as f32);
} else {
// If we're inside the sphere, there's light from every direction.
let shadow_vec = uniform_sample_sphere(u, v) * space.inverse();
let shadow_vec = {
let sample_vec = uniform_sample_sphere(u, v);
let sample_point = (arr + sample_vec).into_vector().normalized() * radius as f32;
let adjusted_sample_point = sample_point * SAMPLE_RADIUS_SHRINK_FACTOR;
(adjusted_sample_point.into_point() - arr) * space.inverse()
};
let pdf = 1.0 / (4.0 * PI_64);
let spectral_sample = (col * surface_area_inv as f32).to_spectral_sample(wavelength);
return (spectral_sample, shadow_vec, pdf as f32);

1
src/main.rs
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@ -44,6 +44,7 @@ mod image;
mod lerp;
mod light;
mod math;
mod mis;
mod parse;
mod ray;
mod renderer;

13
src/mis.rs Normal file
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@ -0,0 +1,13 @@
#![allow(dead_code)]
pub fn balance_heuristic(a: f32, b: f32) -> f32 {
let mis_fac = a / (a + b);
a / mis_fac
}
pub fn power_heuristic(a: f32, b: f32) -> f32 {
let a2 = a * a;
let b2 = b * b;
let mis_fac = a2 / (a2 + b2);
a / mis_fac
}

40
src/renderer.rs
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@ -19,6 +19,7 @@ use hash::hash_u32;
use hilbert;
use image::Image;
use math::{fast_logit, upper_power_of_two};
use mis::power_heuristic;
use ray::Ray;
use scene::Scene;
use surface;
@ -372,8 +373,9 @@ pub struct LightPath {
wavelength: f32,
next_bounce_ray: Option<Ray>,
next_attentuation_fac: Float4,
next_attenuation_fac: Float4,
closure_sample_pdf: f32,
light_attenuation: Float4,
pending_color_addition: Float4,
color: Float4,
@ -401,8 +403,9 @@ impl LightPath {
wavelength: wavelength,
next_bounce_ray: None,
next_attentuation_fac: Float4::splat(1.0),
next_attenuation_fac: Float4::splat(1.0),
closure_sample_pdf: 1.0,
light_attenuation: Float4::splat(1.0),
pending_color_addition: Float4::splat(0.0),
color: Float4::splat(0.0),
@ -449,10 +452,20 @@ impl LightPath {
// - Terminate the path.
use shading::surface_closure::SurfaceClosureUnion;
if let &SurfaceClosureUnion::EmitClosure(ref clsr) = closure {
self.color += clsr.emitted_color().e * self.light_attenuation;
if let LightPathEvent::CameraRay = self.event {
self.color += clsr.emitted_color().e;
} else {
let mis_pdf =
power_heuristic(self.closure_sample_pdf, idata.sample_pdf);
self.color += clsr.emitted_color().e * self.light_attenuation / mis_pdf;
};
return false;
}
// Roll the previous closure pdf into the attentuation
self.light_attenuation /= self.closure_sample_pdf;
// Prepare light ray
let light_n = self.next_lds_samp();
let light_uvw = (
@ -482,11 +495,20 @@ impl LightPath {
material.evaluate(ray.dir, shadow_vec, idata.nor, idata.nor_g);
if attenuation.e.h_max() > 0.0 {
// Calculate MIS
let closure_pdf = material.sample_pdf(
ray.dir,
shadow_vec,
idata.nor,
idata.nor_g,
);
let light_mis_pdf = power_heuristic(light_pdf, closure_pdf);
// Calculate and store the light that will be contributed
// to the film plane if the light is not in shadow.
self.pending_color_addition = light_color.e * attenuation.e *
self.light_attenuation /
(light_pdf * light_sel_pdf);
(light_mis_pdf * light_sel_pdf);
// Calculate the shadow ray for testing if the light is
// in shadow or not.
@ -536,7 +558,8 @@ impl LightPath {
if (pdf > 0.0) && (filter.e.h_max() > 0.0) {
// Account for the additional light attenuation from
// this bounce
self.next_attentuation_fac = filter.e / pdf;
self.next_attenuation_fac = filter.e;
self.closure_sample_pdf = pdf;
// Calculate the ray for this bounce
let offset_pos = robust_ray_origin(
@ -564,7 +587,7 @@ impl LightPath {
} else if do_bounce {
*ray = self.next_bounce_ray.unwrap();
self.event = LightPathEvent::BounceRay;
self.light_attenuation *= self.next_attentuation_fac;
self.light_attenuation *= self.next_attenuation_fac;
return true;
} else {
return false;
@ -575,7 +598,8 @@ impl LightPath {
.world
.background_color
.to_spectral_sample(self.wavelength)
.e * self.light_attenuation;
.e * self.light_attenuation /
self.closure_sample_pdf;
return false;
}
}
@ -592,7 +616,7 @@ impl LightPath {
// Set up for the next bounce, if any
if let Some(ref nbr) = self.next_bounce_ray {
*ray = *nbr;
self.light_attenuation *= self.next_attentuation_fac;
self.light_attenuation *= self.next_attenuation_fac;
self.event = LightPathEvent::BounceRay;
return true;
} else {

17
src/tracer.rs
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@ -185,7 +185,7 @@ impl<'a> TracerInner<'a> {
) {
match *obj {
Object::Surface(surface) => {
let unassigned_shader = SimpleSurfaceShader::Lambert {
let unassigned_shader = SimpleSurfaceShader::Emit {
color: XYZ::from_tuple(rec709_to_xyz((1.0, 0.0, 1.0))),
};
let shader = surface_shader.unwrap_or(&unassigned_shader);
@ -199,8 +199,19 @@ impl<'a> TracerInner<'a> {
);
}
Object::SurfaceLight(_) => {
// TODO
Object::SurfaceLight(surface) => {
// Lights don't use shaders
let bogus_shader = SimpleSurfaceShader::Emit {
color: XYZ::from_tuple(rec709_to_xyz((1.0, 0.0, 1.0))),
};
surface.intersect_rays(
rays,
wrays,
&mut self.isects,
&bogus_shader,
self.xform_stack.top(),
);
}
}
}