Improve names for time, ray values in hittable and derived classes

[hollasch]

We need better names that distinguish between these, instead of using generic t names.

[trevordblack]

We have t for the parametric distance (ray values), time for time

We already have a diagram that has t for parametric distance (figure 2).

What do we change hittable and it's children to?

There's also this egregious example in moving_sphere.h:

point3 cen0, point3 cen1, double t0, double t1, double r, shared_ptr<material> m)
: center0(cen0), center1(cen1), time0(t0), time1(t1), radius(r), mat_ptr(m)

[trevordblack]

t_min, tmin, t_max, tmax

time0, time_0, time1, time_1

t0, tm0, t1, tm1

???

[trevordblack]

I propose:

t_min, t_max, time0, time1, tm0, tm1

[trevordblack]

Or, find a new letter for the parametric distance and start redoing figures, code, and text.

[hollasch]

I think t_min and t_max for t parameters (like with rays) are good, as are time0, time1 for time intervals.

Where would you use tm0 and tm1? Not wild about those.

[trevordblack]

         camera(
             point3 lookfrom,
             point3 lookat,
             vec3   vup,
             double vfov, // vertical field-of-view in degrees
             double aspect_ratio,
             double aperture,
             double focus_dist,
             double t0 = 0,
             double t1 = 0
         ) {
             auto theta = degrees_to_radians(vfov);
             auto h = tan(theta/2);
             auto viewport_height = 2.0 * h;
             auto viewport_width = aspect_ratio * viewport_height;
 
             w = unit_vector(lookfrom - lookat);
             u = unit_vector(cross(vup, w));
             v = cross(w, u);
 
             origin = lookfrom;
             horizontal = focus_dist * viewport_width * u;
             vertical = focus_dist * viewport_height * v;
             lower_left_corner = origin - horizontal/2 - vertical/2 - focus_dist*w;
 
             lens_radius = aperture / 2;
             time0 = t0;
             time1 = t1;
         }

[trevordblack]

Basically in function signatures where we don't want to use time0 time1 because those are already member variables.

Did we standardize on how we wanted to accomplish this?

_time0?

[trevordblack]

we also have member variables _max, and _min in aabb.

So our notation here is inconsistent

[trevordblack]

Oh, and src/*/bvh.h is a mess

[hollasch]

Following up on Slack.

[trevordblack]

Outcome:

• _min -> minimum
• _max -> maximum
• tmax -> t_max
• tmin -> t_min
• t0
• t1