forked from bartvdbraak/blender
376 lines
16 KiB
C++
376 lines
16 KiB
C++
/*
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* Copyright 2011-2020 Blender Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "sky_float3.h"
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#include "sky_model.h"
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/* Constants */
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static const float rayleigh_scale = 8000.0f; // Rayleigh scale height (m)
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static const float mie_scale = 1200.0f; // Mie scale height (m)
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static const float mie_coeff = 2e-5f; // Mie scattering coefficient
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static const float mie_G = 0.76f; // aerosols anisotropy
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static const float sqr_G = mie_G * mie_G; // squared aerosols anisotropy
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static const float earth_radius = 6360000.0f; // radius of Earth (m)
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static const float atmosphere_radius = 6420000.0f; // radius of atmosphere (m)
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static const int steps = 32; // segments per primary ray
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static const int steps_light = 16; // segments per sun connection ray
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static const int num_wavelengths = 21; // number of wavelengths
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static const int max_luminous_efficacy = 683; // maximum luminous efficacy
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static const float step_lambda = (num_wavelengths - 1) *
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1e-9f; // step between each sampled wavelength
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/* irradiance at top of atmosphere */
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static const float irradiance[] = {
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1.45756829855592995315f, 1.56596305559738380175f, 1.65148449067670455293f,
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1.71496242737209314555f, 1.75797983805020541226f, 1.78256407885924539336f,
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1.79095108475838560302f, 1.78541550133410664714f, 1.76815554864306845317f,
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1.74122069647250410362f, 1.70647127164943679389f, 1.66556087452739887134f,
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1.61993437242451854274f, 1.57083597368892080581f, 1.51932335059305478886f,
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1.46628494965214395407f, 1.41245852740172450623f, 1.35844961970384092709f,
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1.30474913844739281998f, 1.25174963272610817455f, 1.19975998755420620867f};
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/* Rayleigh scattering coefficient */
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static const float rayleigh_coeff[] = {
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0.00005424820087636473f, 0.00004418549866505454f, 0.00003635151910165377f,
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0.00003017929012024763f, 0.00002526320226989157f, 0.00002130859310621843f,
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0.00001809838025320633f, 0.00001547057129129042f, 0.00001330284977336850f,
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0.00001150184784075764f, 0.00000999557429990163f, 0.00000872799973630707f,
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0.00000765513700977967f, 0.00000674217203751443f, 0.00000596134125832052f,
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0.00000529034598065810f, 0.00000471115687557433f, 0.00000420910481110487f,
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0.00000377218381260133f, 0.00000339051255477280f, 0.00000305591531679811f};
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/* Ozone absorption coefficient */
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static const float ozone_coeff[] = {
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0.00000000325126849861f, 0.00000000585395365047f, 0.00000001977191155085f,
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0.00000007309568762914f, 0.00000020084561514287f, 0.00000040383958096161f,
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0.00000063551335912363f, 0.00000096707041180970f, 0.00000154797400424410f,
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0.00000209038647223331f, 0.00000246128056164565f, 0.00000273551299461512f,
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0.00000215125863128643f, 0.00000159051840791988f, 0.00000112356197979857f,
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0.00000073527551487574f, 0.00000046450130357806f, 0.00000033096079921048f,
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0.00000022512612292678f, 0.00000014879129266490f, 0.00000016828623364192f};
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/* CIE XYZ color matching functions */
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static const float cmf_xyz[][3] = {{0.00136800000f, 0.00003900000f, 0.00645000100f},
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{0.01431000000f, 0.00039600000f, 0.06785001000f},
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{0.13438000000f, 0.00400000000f, 0.64560000000f},
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{0.34828000000f, 0.02300000000f, 1.74706000000f},
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{0.29080000000f, 0.06000000000f, 1.66920000000f},
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{0.09564000000f, 0.13902000000f, 0.81295010000f},
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{0.00490000000f, 0.32300000000f, 0.27200000000f},
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{0.06327000000f, 0.71000000000f, 0.07824999000f},
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{0.29040000000f, 0.95400000000f, 0.02030000000f},
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{0.59450000000f, 0.99500000000f, 0.00390000000f},
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{0.91630000000f, 0.87000000000f, 0.00165000100f},
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{1.06220000000f, 0.63100000000f, 0.00080000000f},
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{0.85444990000f, 0.38100000000f, 0.00019000000f},
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{0.44790000000f, 0.17500000000f, 0.00002000000f},
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{0.16490000000f, 0.06100000000f, 0.00000000000f},
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{0.04677000000f, 0.01700000000f, 0.00000000000f},
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{0.01135916000f, 0.00410200000f, 0.00000000000f},
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{0.00289932700f, 0.00104700000f, 0.00000000000f},
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{0.00069007860f, 0.00024920000f, 0.00000000000f},
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{0.00016615050f, 0.00006000000f, 0.00000000000f},
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{0.00004150994f, 0.00001499000f, 0.00000000000f}};
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static float3 geographical_to_direction(float lat, float lon)
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{
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return make_float3(cosf(lat) * cosf(lon), cosf(lat) * sinf(lon), sinf(lat));
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}
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static float3 spec_to_xyz(float *spectrum)
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{
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float3 xyz = make_float3(0.0f, 0.0f, 0.0f);
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for (int i = 0; i < num_wavelengths; i++) {
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xyz.x += cmf_xyz[i][0] * spectrum[i];
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xyz.y += cmf_xyz[i][1] * spectrum[i];
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xyz.z += cmf_xyz[i][2] * spectrum[i];
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}
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return xyz * step_lambda * max_luminous_efficacy;
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}
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/* Atmosphere volume models */
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static float density_rayleigh(float height)
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{
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return expf(-height / rayleigh_scale);
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}
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static float density_mie(float height)
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{
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return expf(-height / mie_scale);
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}
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static float density_ozone(float height)
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{
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float den = 0.0f;
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if (height >= 10000.0f && height < 25000.0f)
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den = 1.0f / 15000.0f * height - 2.0f / 3.0f;
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else if (height >= 25000 && height < 40000)
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den = -(1.0f / 15000.0f * height - 8.0f / 3.0f);
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return den;
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}
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static float phase_rayleigh(float mu)
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{
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return 3.0f / (16.0f * M_PI_F) * (1.0f + sqr(mu));
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}
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static float phase_mie(float mu)
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{
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return (3.0f * (1.0f - sqr_G) * (1.0f + sqr(mu))) /
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(8.0f * M_PI_F * (2.0f + sqr_G) * powf((1.0f + sqr_G - 2.0f * mie_G * mu), 1.5));
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}
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/* Intersection helpers */
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static bool surface_intersection(float3 pos, float3 dir)
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{
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if (dir.z >= 0)
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return false;
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float t = dot(dir, -pos) / len_squared(dir);
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float D = pos.x * pos.x - 2.0f * (-pos.x) * dir.x * t + dir.x * t * dir.x * t + pos.y * pos.y -
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2.0f * (-pos.y) * dir.y * t + (dir.y * t) * (dir.y * t) + pos.z * pos.z -
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2.0f * (-pos.z) * dir.z * t + dir.z * t * dir.z * t;
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return (D <= sqr(earth_radius));
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}
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static float3 atmosphere_intersection(float3 pos, float3 dir)
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{
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float b = -2.0f * dot(dir, -pos);
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float c = len_squared(pos) - sqr(atmosphere_radius);
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float t = (-b + sqrtf(b * b - 4.0f * c)) / 2.0f;
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return make_float3(pos.x + dir.x * t, pos.y + dir.y * t, pos.z + dir.z * t);
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}
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static float3 ray_optical_depth(float3 ray_origin, float3 ray_dir)
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{
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/* This code computes the optical depth along a ray through the atmosphere. */
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float3 ray_end = atmosphere_intersection(ray_origin, ray_dir);
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float ray_length = distance(ray_origin, ray_end);
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/* To compute the optical depth, we step along the ray in segments and
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* accumulate the optical depth along each segment. */
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float segment_length = ray_length / steps_light;
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float3 segment = segment_length * ray_dir;
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/* Instead of tracking the transmission spectrum across all wavelengths directly,
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* we use the fact that the density always has the same spectrum for each type of
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* scattering, so we split the density into a constant spectrum and a factor and
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* only track the factors. */
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float3 optical_depth = make_float3(0.0f, 0.0f, 0.0f);
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/* The density of each segment is evaluated at its middle. */
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float3 P = ray_origin + 0.5f * segment;
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for (int i = 0; i < steps_light; i++) {
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/* Compute height above sea level. */
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float height = len(P) - earth_radius;
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/* Accumulate optical depth of this segment (density is assumed to be constant along it). */
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float3 density = make_float3(
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density_rayleigh(height), density_mie(height), density_ozone(height));
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optical_depth += density;
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/* Advance along ray. */
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P += segment;
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}
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return optical_depth * segment_length;
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}
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/* Single Scattering implementation */
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static void single_scattering(float3 ray_dir,
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float3 sun_dir,
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float3 ray_origin,
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float air_density,
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float dust_density,
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float ozone_density,
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float *r_spectrum)
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{
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/* This code computes single-inscattering along a ray through the atmosphere. */
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float3 ray_end = atmosphere_intersection(ray_origin, ray_dir);
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float ray_length = distance(ray_origin, ray_end);
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/* To compute the inscattering, we step along the ray in segments and accumulate
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* the inscattering as well as the optical depth along each segment. */
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float segment_length = ray_length / steps;
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float3 segment = segment_length * ray_dir;
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/* Instead of tracking the transmission spectrum across all wavelengths directly,
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* we use the fact that the density always has the same spectrum for each type of
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* scattering, so we split the density into a constant spectrum and a factor and
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* only track the factors. */
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float3 optical_depth = make_float3(0.0f, 0.0f, 0.0f);
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/* Zero out light accumulation. */
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for (int wl = 0; wl < num_wavelengths; wl++) {
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r_spectrum[wl] = 0.0f;
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}
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/* Compute phase function for scattering and the density scale factor. */
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float mu = dot(ray_dir, sun_dir);
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float3 phase_function = make_float3(phase_rayleigh(mu), phase_mie(mu), 0.0f);
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float3 density_scale = make_float3(air_density, dust_density, ozone_density);
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/* The density and in-scattering of each segment is evaluated at its middle. */
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float3 P = ray_origin + 0.5f * segment;
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for (int i = 0; i < steps; i++) {
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/* Compute height above sea level. */
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float height = len(P) - earth_radius;
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/* Evaluate and accumulate optical depth along the ray. */
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float3 density = density_scale * make_float3(density_rayleigh(height),
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density_mie(height),
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density_ozone(height));
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optical_depth += segment_length * density;
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/* If the earth isn't in the way, evaluate inscattering from the sun. */
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if (!surface_intersection(P, sun_dir)) {
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float3 light_optical_depth = density_scale * ray_optical_depth(P, sun_dir);
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float3 total_optical_depth = optical_depth + light_optical_depth;
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/* attenuation of light */
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for (int wl = 0; wl < num_wavelengths; wl++) {
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float3 extinction_density = total_optical_depth * make_float3(rayleigh_coeff[wl],
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1.11f * mie_coeff,
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ozone_coeff[wl]);
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float attenuation = expf(-reduce_add(extinction_density));
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float3 scattering_density = density * make_float3(rayleigh_coeff[wl], mie_coeff, 0.0f);
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/* The total inscattered radiance from one segment is:
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* Tr(A<->B) * Tr(B<->C) * sigma_s * phase * L * segment_length
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*
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* These terms are:
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* Tr(A<->B): Transmission from start to scattering position (tracked in optical_depth)
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* Tr(B<->C): Transmission from scattering position to light (computed in
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* ray_optical_depth) sigma_s: Scattering density phase: Phase function of the scattering
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* type (Rayleigh or Mie) L: Radiance coming from the light source segment_length: The
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* length of the segment
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*
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* The code here is just that, with a bit of additional optimization to not store full
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* spectra for the optical depth.
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*/
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r_spectrum[wl] += attenuation * reduce_add(phase_function * scattering_density) *
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irradiance[wl] * segment_length;
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}
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}
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/* Advance along ray. */
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P += segment;
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}
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}
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/* calculate texture array */
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void SKY_nishita_skymodel_precompute_texture(float *pixels,
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int stride,
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int start_y,
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int end_y,
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int width,
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int height,
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float sun_elevation,
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float altitude,
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float air_density,
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float dust_density,
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float ozone_density)
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{
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/* calculate texture pixels */
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float spectrum[num_wavelengths];
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int half_width = width / 2;
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float3 cam_pos = make_float3(0, 0, earth_radius + altitude);
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float3 sun_dir = geographical_to_direction(sun_elevation, 0.0f);
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float latitude_step = M_PI_2_F / height;
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float longitude_step = M_2PI_F / width;
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float half_lat_step = latitude_step / 2.0f;
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for (int y = start_y; y < end_y; y++) {
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/* sample more pixels toward the horizon */
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float latitude = (M_PI_2_F + half_lat_step) * sqr((float)y / height);
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float *pixel_row = pixels + (y * width * stride);
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for (int x = 0; x < half_width; x++) {
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float longitude = longitude_step * x - M_PI_F;
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float3 dir = geographical_to_direction(latitude, longitude);
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single_scattering(dir, sun_dir, cam_pos, air_density, dust_density, ozone_density, spectrum);
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float3 xyz = spec_to_xyz(spectrum);
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int pos_x = x * stride;
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pixel_row[pos_x] = xyz.x;
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pixel_row[pos_x + 1] = xyz.y;
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pixel_row[pos_x + 2] = xyz.z;
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/* mirror sky */
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int mirror_x = (width - x - 1) * stride;
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pixel_row[mirror_x] = xyz.x;
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pixel_row[mirror_x + 1] = xyz.y;
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pixel_row[mirror_x + 2] = xyz.z;
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}
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}
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}
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/* Sun disc */
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static void sun_radiation(float3 cam_dir,
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float altitude,
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float air_density,
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float dust_density,
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float solid_angle,
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float *r_spectrum)
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{
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float3 cam_pos = make_float3(0, 0, earth_radius + altitude);
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float3 optical_depth = ray_optical_depth(cam_pos, cam_dir);
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/* Compute final spectrum. */
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for (int i = 0; i < num_wavelengths; i++) {
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/* Combine spectra and the optical depth into transmittance. */
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float transmittance = rayleigh_coeff[i] * optical_depth.x * air_density +
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1.11f * mie_coeff * optical_depth.y * dust_density;
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r_spectrum[i] = irradiance[i] * expf(-transmittance) / solid_angle;
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}
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}
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void SKY_nishita_skymodel_precompute_sun(float sun_elevation,
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float angular_diameter,
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float altitude,
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float air_density,
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float dust_density,
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float *r_pixel_bottom,
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float *r_pixel_top)
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{
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/* definitions */
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float half_angular = angular_diameter / 2.0f;
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float solid_angle = M_2PI_F * (1.0f - cosf(half_angular));
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float spectrum[num_wavelengths];
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float bottom = sun_elevation - half_angular;
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float top = sun_elevation + half_angular;
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float elevation_bottom, elevation_top;
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float3 pix_bottom, pix_top, sun_dir;
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/* compute 2 pixels for sun disc */
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elevation_bottom = (bottom > 0.0f) ? bottom : 0.0f;
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elevation_top = (top > 0.0f) ? top : 0.0f;
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sun_dir = geographical_to_direction(elevation_bottom, 0.0f);
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sun_radiation(sun_dir, altitude, air_density, dust_density, solid_angle, spectrum);
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pix_bottom = spec_to_xyz(spectrum);
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sun_dir = geographical_to_direction(elevation_top, 0.0f);
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sun_radiation(sun_dir, altitude, air_density, dust_density, solid_angle, spectrum);
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pix_top = spec_to_xyz(spectrum);
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/* store pixels */
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r_pixel_bottom[0] = pix_bottom.x;
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r_pixel_bottom[1] = pix_bottom.y;
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r_pixel_bottom[2] = pix_bottom.z;
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r_pixel_top[0] = pix_top.x;
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r_pixel_top[1] = pix_top.y;
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r_pixel_top[2] = pix_top.z;
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}
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