diff options
Diffstat (limited to 'raymarch.cl')
| -rw-r--r-- | raymarch.cl | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/raymarch.cl b/raymarch.cl new file mode 100644 index 0000000..d6a771d --- /dev/null +++ b/raymarch.cl @@ -0,0 +1,175 @@ +__constant double earth_radius = $earth_radius; +__constant double atmos_height = $atmos_height; + +__constant double rayleigh_atmos_height = $rayleigh_atmos_height; +__constant double mie_atmos_height = $mie_atmos_height; + +__constant double3 rayleigh_beta = (double3)$rayleigh_beta; +__constant double3 mie_beta = (double3)$mie_beta; + +__constant int ray_samples = $ray_samples; +__constant int light_samples = $light_samples; + +__constant double exposure = $exposure; + +bool insideAtmosphere(double3 pos) { + return length(pos) < earth_radius + atmos_height; +} + +double altitude(double3 pos) { + return length(pos) - earth_radius; +} + +// solve x^2 + px + q +bool solvePolynomialOfDegreeTwo(double p, double q, double* x1, double* x2) { + const double pHalf = 0.5*p; + const double inner = pHalf*pHalf - q; + + if (inner >= 0.0) { + *x1 = -pHalf + sqrt(inner); + *x2 = -pHalf - sqrt(inner); + return true; + } else { + return false; + } +} + +// interection of origin + d*dir and a sphere of radius r for normalized dir +bool solveRaySphereIntersection(double3 origin, double3 dir, double r, double* d0, double* d1) { + const double p = 2 * dot(dir,origin); + const double q = dot(origin,origin) - r*r; + + if (solvePolynomialOfDegreeTwo(p, q, d0, d1)) { + if (*d0 > *d1) { + double tmp = *d1; + *d1 = *d0; + *d0 = tmp; + } + return true; + } else { + return false; + } +} + +double2 getNormalizedScreenPos(double x, double y) { + return (double2)( + 2.0 * (x / $size_x - 0.5) * $size_x.0 / $size_y.0, + 2.0 * (y / $size_y - 0.5) + ); +} + +double3 getEyeRayDir(double2 screen_pos, double3 eye_pos, double3 eye_target) { + const double3 forward = normalize(eye_target - eye_pos); + const double3 right = normalize(cross((double3)(0.0, 0.0, 1.0), forward)); + const double3 up = normalize(cross(forward, right)); + + return normalize(screen_pos.x*right + screen_pos.y*up + 1.5*forward); +} + +bool isVisible(double3 origin, double3 dir) { + double e0, e1; + return !solveRaySphereIntersection(origin, dir, earth_radius, &e0, &e1) + || (e0 < 0 && e1 < 0); +} + +double lengthOfRayInAtmosphere(double3 origin, double3 dir) { + double d0, d1; + solveRaySphereIntersection(origin, dir, earth_radius + atmos_height, &d0, &d1); + return d1 - d0; +} + +double3 scatter(double3 origin, double3 dir, double dist, double3 sun) { + double3 rayleigh_sum = 0.0; + double3 mie_sum = 0.0; + + double rayleigh_depth = 0.0; + double mie_depth = 0.0; + + const double h = dist / ray_samples; + + for (int i = 0; i < ray_samples; ++i) { + double3 curr = origin + (i+0.5)*h*dir; + + if (isVisible(curr, sun)) { + double height = altitude(curr); + + double rayleigh_h = exp(-height / rayleigh_atmos_height) * h; + double mie_h = exp(-height / mie_atmos_height) * h; + + rayleigh_depth += rayleigh_h; + mie_depth += mie_h; + + double light_h = lengthOfRayInAtmosphere(curr, sun) / light_samples; + + double rayleigh_light_depth = 0; + double mie_light_depth = 0; + + for (int j = 0; j < light_samples; ++j) { + height = altitude(curr + (j+0.5)*light_h*sun); + + rayleigh_light_depth += exp(-height / rayleigh_atmos_height) * light_h; + mie_light_depth += exp(-height / mie_atmos_height) * light_h; + } + + double3 tau = rayleigh_beta*(rayleigh_depth+rayleigh_light_depth) + mie_beta*(mie_depth+ mie_light_depth); + double3 attenuation = exp(-tau); + + rayleigh_sum += attenuation * rayleigh_h; + mie_sum += attenuation * mie_h; + } + } + + const double mu = dot(dir,sun); + const double rayleigh_phase = 3. / (16.*M_PI) * (1.0 + mu*mu); + const double g = 0.8; + const double mie_phase = 3. / (8.*M_PI) * ((1. - g*g) * (1. + mu*mu)) / ((2. + g*g) * pow(1. + g*g - 2.*g*mu, 1.5)); + + return rayleigh_sum*rayleigh_beta*rayleigh_phase + mie_sum*mie_beta*mie_phase; +} + +void setColor(__global double* result, unsigned x, unsigned y, double3 color) { + result[3*$size_x*y + 3*x + 0] = color.x; + result[3*$size_x*y + 3*x + 1] = color.y; + result[3*$size_x*y + 3*x + 2] = color.z; +} + +__kernel void render(__global double* result, double3 eye_pos, double3 eye_dir, double3 sun) { + eye_pos *= earth_radius; + eye_dir *= earth_radius; + + const unsigned x = get_global_id(0); + const unsigned y = get_global_id(1); + + double2 screen_pos = getNormalizedScreenPos(x, y); + double3 ray_dir = getEyeRayDir(screen_pos, eye_pos, eye_pos + eye_dir); + + double d0, d1; + + if (!solveRaySphereIntersection(eye_pos, ray_dir, earth_radius + atmos_height, &d0, &d1)) { + setColor(result, x, y, 0.0); + return; + } + + double min_dist = d0; + double max_dist = d1; + + if (insideAtmosphere(eye_pos)) { + min_dist = 0.0; + + if (solveRaySphereIntersection(eye_pos, ray_dir, earth_radius, &d0, &d1) && d1 > 0) { + max_dist = max(0.0, d0); + } + } else { + if (solveRaySphereIntersection(eye_pos, ray_dir, earth_radius, &d0, &d1)) { + max_dist = d0; + } + } + + const double3 ray_origin = eye_pos + min_dist*ray_dir; + const double ray_length = max_dist - min_dist; + + double3 color = scatter(ray_origin, ray_dir, ray_length, normalize(sun)); + color = 1.0 - exp(-exposure * color); + + setColor(result, x, y, color); +} |