# 【GLSL】レイマーチングでソフトシャドウ

```#define PI 3.14159265359
#define TWO_PI PI * 2.0
#define HALF_PI PI / 2.0

precision mediump float;

uniform float u_time;
uniform vec2 u_mouse;
uniform vec2 u_resolution;

struct Camera {
vec3 position;
vec3 ray;
};

float random(float v) {
return fract(sin(v) * 43758.5453123);
}

float smoothmin(float d1, float d2, float k) {
return -log(exp(-k * d1) + exp(-k * d2)) / k;
}

vec3 repeat(vec3 p, vec3 interval) {
return mod(p, interval) - interval / 2.0;
}

vec3 repeatX(vec3 p, float interval) {
return vec3(mod(p.x, interval) - interval / 2.0, p.y, p.z);
}

vec3 repeatY(vec3 p, float interval) {
return vec3(p.x, mod(p.y, interval) - interval / 2.0, p.z);
}

vec3 repeatZ(vec3 p, float interval) {
return vec3(p.x, p.y, mod(p.z, interval) - interval / 2.0);
}

vec3 rotateX(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(1, 0.0, 0.0),
vec3(0.0, c, -s),
vec3(0.0, s, c));
return m * p;
}

vec3 rotateY(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(c, 0.0, s),
vec3(0.0, 1.0, 0.0),
vec3(-s, 0.0, c));
return m * p;
}

vec3 rotateZ(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(c, -s, 0.0),
vec3(s, c, 0.0),
vec3(0.0, 0.0, 1.0));
return m * p;
}

vec3 translate(vec3 p, vec3 t) {
mat4 m = mat4(vec4(1.0, 0.0, 0.0, 0.0),
vec4(0.0, 1.0, 0.0, 0.0),
vec4(0.0, 0.0, 1.0, 0.0),
vec4(-t.x, -t.y, -t.z, 1.0));

return (m * vec4(p, 1.0)).xyz;
}

float calcBoxDistance(vec3 p, vec3 size) {
return length(max(abs(p) - size, 0.0));
}

float calcRoundBoxDistance(vec3 p, vec3 size, float r) {
return calcBoxDistance(p, size) - r;
}

float calcSphereDistance(vec3 p, float size) {
return length(p) - size;
}

float calcPlainDistance(vec3 p, vec3 n) {
return dot(p, n);
}

float calcTorusDistance(vec3 p, vec2 size) {
vec2 q = vec2(length(p.xz) - size.x, p.y);
return length(q) - size.y;
}

float calcCylinderDistance(vec3 p, vec3 size) {
return length(p.xz - size.xy) - size.z;
}

float calcDistance(vec3 p) {
float d = 10000000.0;
d = min(d, calcSphereDistance(translate(p, vec3(0.0, 3.0, 0.0)), 1.0));
d = min(d, calcPlainDistance(p, vec3(0.0, 1.0, 0.0)));
return d;
}

vec3 calcNormal(vec3 p) {
float delta = 0.00001;
return normalize(vec3(
calcDistance(p + vec3(delta, 0.0, 0.0)) - calcDistance(p - vec3(delta, 0.0, 0.0)),
calcDistance(p + vec3(0.0, delta, 0.0)) - calcDistance(p - vec3(0.0, delta, 0.0)),
calcDistance(p + vec3(0.0, 0.0, delta)) - calcDistance(p - vec3(0.0, 0.0, delta))
));
}

Camera getPerspectiveCamera(vec2 pos, vec3 eye, vec3 center, vec3 top, float fov) {
float camRadian = fov / 2.0 * PI / 180.0;
vec3 viewDir = normalize(center - eye);
vec3 camSide = cross(viewDir, top);
vec3 camTop = cross(camSide, viewDir);

Camera camera;
camera.position = eye;
camera.ray = normalize(camTop * sin(camRadian * pos.y) + camSide * sin(camRadian * pos.x) + viewDir * cos(camRadian * pos.x));
return camera;
}

Camera getOrthographicCamera(vec2 pos, vec3 eye, vec3 center, vec3 top, float width, float height) {
vec3 viewDir = normalize(center - eye);
vec3 camSide = cross(viewDir, top);
vec3 camTop = cross(camSide, viewDir);

Camera camera;
camera.position = eye + vec3(camTop * pos.y * height / 2.0 + camSide * pos.x * width / 2.0);
camera.ray = viewDir;
return camera;
}

float calcShadow(vec3 pos, vec3 light) {
vec3 lightDir = normalize(light - pos);
float depth = 0.01;
float d;
for (int i = 0; i < 16; i++) {
d = calcDistance(pos + lightDir * depth);
depth += d;
}
return d < 0.001 ? 0.3 : 1.0;
}

float calcSoftShadow(vec3 pos, vec3 light) {
vec3 lightDir = normalize(light - pos);
float depth = 0.001;
float bright = 1.0;
float d;

for (int i = 0; i < 16; i++) {
d = calcDistance(pos + lightDir * depth);
if (d < 0.001) {
}
bright = min(bright, shadowSharpness * d / depth);
depth += d;
}
return 1.0 - (1.0 - bright) * shadowIntensity;
}

void main(void) {
vec2 st = (gl_FragCoord.xy * 2.0 - u_resolution) / min(u_resolution.x, u_resolution.y);
vec2 mouse = (u_mouse * 2.0 - u_resolution) / min(u_resolution.x, u_resolution.y);

vec3 cameraPosition = vec3(7.0, 7.0, 10.0);
vec3 viewCenter = vec3(0.0);
vec3 cameraTop = vec3(0.0, 1.0, 0.0);
Camera camera = getPerspectiveCamera(st, cameraPosition, viewCenter, vec3(0.0, 1.0, 0.0), 60.0);
// Camera camera = getOrthographicCamera(st, cameraPosition, viewCenter, vec3(0.0, 1.0, 0.0), 50.0, 50.0);
vec3 rayPosition = camera.position;
vec3 rayDirection = camera.ray;

float radian = u_time * 0.0003;
vec3 lightPosition = vec3(10.0 * cos(mouse.x * PI), 10.0 * sin(abs(mouse.y) * HALF_PI) + 2.0, 10.0 * sin(mouse.x * PI));
vec3 color = vec3(0.0);
float d;
for (int i = 0; i < 256; i++) {
d = calcDistance(rayPosition);
rayPosition += rayDirection * d;
}

if (d < 0.0001) {
vec3 normal = calcNormal(rayPosition);