Soft Shadows and Ambient Occlusion

// The Common pass is prepended to the Image pass before compilation, so this
// is shared source rather than a second shader. The scene itself is declared
// here and defined in the Image pass, which is where the lesson lives.
float mapScene(vec3 position);

vec3 cameraRay(vec2 fragCoord, vec3 origin, vec3 target, float lens) {
    vec2 uv = (fragCoord - 0.5 * iResolution.xy) / iResolution.y;
    vec3 forward = normalize(target - origin);
    vec3 right = normalize(cross(vec3(0.0, 1.0, 0.0), forward));
    vec3 up = cross(forward, right);
    return normalize(forward * lens + right * uv.x + up * uv.y);
}

float marchScene(vec3 origin, vec3 direction, float maxDistance) {
    float travelled = 0.0;
    for (int i = 0; i < 96; i++) {
        vec3 position = origin + direction * travelled;
        float dist = mapScene(position);
        if (dist < 0.001) return travelled;
        travelled += dist;
        if (travelled > maxDistance) break;
    }
    return -1.0;
}

vec3 sceneNormal(vec3 position, float epsilon) {
    vec2 offset = vec2(epsilon, 0.0);
    return normalize(vec3(
        mapScene(position + offset.xyy) - mapScene(position - offset.xyy),
        mapScene(position + offset.yxy) - mapScene(position - offset.yxy),
        mapScene(position + offset.yyx) - mapScene(position - offset.yyx)));
}

vec3 skyColor(vec3 direction) {
    return mix(vec3(0.05, 0.07, 0.12), vec3(0.16, 0.22, 0.34), direction.y * 0.5 + 0.5);
}