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#version 330 core
in vec3 f_p;
out vec4 f_color;
uniform vec3 u_cam;
uniform float u_time;
uniform int u_mode;
uniform float u_sigma;
// Ray-AABB intersection
// ref: https://tavianator.com/2022/ray_box_boundary.html
bool intersect(vec3 ro, vec3 rd, vec3 bbmin, vec3 bbmax, out float t0, out float t1)
{
vec3 inv = 1.0f / rd;
vec3 ta = (bbmin - ro) * inv;
vec3 tb = (bbmax - ro) * inv;
vec3 tmin = min(ta, tb);
vec3 tmax = max(ta, tb);
t0 = max(max(tmin.x, tmin.y), tmin.z);
t1 = min(min(tmax.x, tmax.y), tmax.z);
return t1 >= max(t0, 0.0f);
}
// Mode 0: Basic
void main_0()
{
vec3 bbmin = vec3(0.0f, 0.0f, 0.0f);
vec3 bbmax = vec3(1.0f, 1.0f, 1.0f);
vec3 ro = u_cam;
vec3 rd = normalize(f_p - ro);
float t0 = 0.0f;
float t1 = 0.0f;
if (!intersect(ro, rd, bbmin, bbmax, t0, t1)) {
f_color = vec4(0.0f, 0.0f, 0.0f, 0.0f);
return;
}
// Clamp entry point in front of camera
float t_enter = max(t0, 0.0f);
float t_exit = t1;
float t_len = max(0.0f, t_exit - t_enter);
// Beer-Lambert attenuation
// ref: https://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law
float a = 1.0f - exp(-u_sigma * t_len);
f_color = vec4(vec3(1.0f), a);
}
void main()
{
switch (u_mode) {
case 0: { main_0(); } break;
default: { f_color = vec4(0.0f, 1.0f, 0.0f, 1.0f); } break;
}
}
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