Ch 11 Reflection / Refraction Problem

Thank you Jamis I finally found out what was the issue, since you told me that the problem might be with the intersection between the sphere and the checkered Plane,
I checked out the Plane and I realized that I was doing one of the mistakes that you warn us about:

so basically I was doing the transform multiplication in the wrong order it was like this:

rotation_x(pi/2) * translationMatrix(0, 0, 10)

i changed it like this:

translationMatrix(0, 0, 10) * rotation_x(pi/2)

and I got this finally: 



I think this might be it this time.

thanks again,

for anyone who had the same problem as mine ,
just follow this 2 steps:
1. pass all the intersections even those inferior to zero in you Intersect_world function. as tdaines and Jamis mentioned
2.check your Plane transformation if the order of your multiplication is correct.
 that should do the work, and sorry for my English still learning

Adding this for anyone who got stuck because I spent way too long trying to figure this out, make sure you negate your normal vector before calculating the under_point

So I find myself stuck at the same point, but with a decidedly different problem.  Hopefully people are still paying attention to this, because I am afraid I am at a loss.  So far my code has been able to pass every test up through Chapter 11 Test #8 (Handling Refraction in shade_hit) but when I try to render the scene that people are discussing here, mine comes out blocky, or seemingly low resolution inside the glass sphere and I really haven't an idea why.

Here is the glass marble by itself


And here it is with the air bubble added to the center of it.


If you zoom in, you can see that there are essentially chunks of the same color in 4-9-16 pixel sizes that are the same color and I am quite unsure of why.  I suspect it has to do with my color_at function which I can repost here (or can be found in my github repo: F# RayTracer)

I attempted to mimic the output on the previous page and I find that my initial call to prepare_computations (at 125,125 mimicking the scene on the previous page) give the same t values and refractive indices



In precompute

Main intersection is at t = 4.028495995, object id = 3
       t_val 4.028495995
       obj id 3
       n idx 1.5
       t_val 4.568385678
       obj id 4
       n idx 1.0000034
       t_val 5.417668679
       obj id 4
       n idx 1.0000034
       t_val 5.957558362
       obj id 3
       n idx 1.5
       t_val 15.02094768
       obj id 2
       n idx 1.0In here obj 2 = floor, 3 = glass marble, 4 = air bubble.

Once I go on to compute the color at 125, 125, I get completely different results which makes this frustrating to try and match up, I don't even seem to reach the same recursion depth, which makes me wonder if I am not doing something simple and incorrect.  I do match up on Jamis' last four entries for all the terms EXCEPT the color (well except the color after the first time where we do match).  What I see is that I never reach the same recursion depth, once I reach a depth of 2 (1, I could be off by one in my counting here) then the ray intersects the floor which is non transparent and we start building back up.
== Remaining 2 ==
Reached non-transparent item id 2 true
Under total internal reflection false
out of recursion moves false
== Remaining 3 ==
Object id # 3
n1 1.5
n2 1.0
eyev (0.24617184789842556, -0.24617184789842556, -0.9374427143055457, -0)
normalv (0.3589807284374399, -0.3589807284374399, -0.861548416063224, -0)
under point (-0.35898431824472427, 0.35898431824472427, 0.8615570315473846, 1)
n ratio 1.5
cos_i 0.9843941842
sin2_t 0.06967820267
cos_t 0.9645319058
refract direction (-0.18543832601633745, 0.18543832601633745, 0.9650001318593266, 0)
refracted color RGB(0.6692438880894562, 0.6692438880894562, 0.6692438880894562)
== Remaining 4 ==
Object id # 4
n1 1.0000034
n2 1.5
eyev (0.11201785698040068, -0.11201785698040068, -0.9873722699342115, -0)
normalv (0.4637181819920862, -0.4637181819920862, -0.754937676487211, -0)
under point (-0.231863728177863, 0.231863728177863, 0.37747638762037033, 1)
n ratio 0.6666689333
cos_i 0.8492939613
sin2_t 0.1238674056
cos_t 0.9360195481
refract direction (-0.24617184789842556, 0.24617184789842556, 0.9374427143055457, 0)
refracted color RGB(1.0857648825025026, 1.0857648825025026, 1.0857648825025026)
== Remaining 5 ==
Object id # 4
n1 1.5
n2 1.0000034
eyev (-0.02645089737072017, 0.02645089737072017, -0.9993001051018494, -0)
normalv (-0.2734541100138954, 0.2734541100138954, -0.922196128506847, 0)
under point (-0.13672432046584757, 0.13672432046584757, -0.4610888422921384, 1)
n ratio 1.4999949
cos_i 0.9360169013
sin2_t 0.2787109157
cos_t 0.849287398
refract direction (-0.11201785698040068, 0.11201785698040068, 0.9873722699342115, 0)
refracted color RGB(0.9771883942522523, 0.9771883942522523, 0.9771883942522523)
== Remaining 6 ==
Object id # 3
n1 1.0
n2 1.5
eyev (0.03733084416743292, -0.03733084416743292, -0.9986054356689101, -0)
normalv (-0.15038715621763504, 0.15038715621763504, -0.9771220018449821, 0)
under point (-0.1503856523460725, 0.1503856523460725, -0.9771122306249613, 1)
n ratio 0.6666666667
cos_i 0.9645311834
sin2_t 0.03096870947
cos_t 0.9843938696
refract direction (0.02645089737072017, -0.02645089737072017, 0.9993001051018494, 0)
refracted color RGB(1.2710603727077006, 1.2710603727077006, 1.2710603727077006)
Here is my relevant code (with logging that isn't checked into github) hopefully someone can hit me with a clue by four and show me what I am missing.


let rec shade_hit (p: PreCompute) (w: World) (d: int) (logIt: bool): Color =
   let mat = extract_obj p |> extract_material
   let in_shadow = is_shadowed w (extract_over_point p)
   let surface = lights w
                 |> List.map (fun l -> lighting mat (extract_obj p) l (extract_over_point p) (extract_eyev p) (extract_normalv p) in_shadow)
                 |> List.fold (fun acc c -> acc + c) (Color(0,0,0))
   let reflect = reflected_color w p d false
   let refract = refracted_color w p d logIt
   surface + reflect + refract
and color_at (w: World) (r: Ray) (d: int) (logIt: bool): Color =
   let its = intersect_world r w
   match hit its with
   | Some i -> shade_hit (prepare_computations i r its logIt) w d logIt
   | None -> Color(0,0,0)
and reflected_color w p d logIt =
   if d < 1 then
       black
   else
       let reflect_val = extract_obj p |> extract_material |> reflective
       if reflect_val = 0.0 then
           black
       else
           let reflect_ray = make_ray (extract_over_point p) (extract_reflectv p)
           let c = color_at w reflect_ray (d-1) logIt
           c * reflect_val
and refracted_color (w: World) (comps: PreCompute) (remaining: int) (logIt: bool): Color =
   let t = comps |> extract_obj |> extract_material |> transparency // gets the transparency value of the material in the precompute structure
   let n1 = extract_n1 comps
   let n2 = extract_n2 comps
   let o = extract_obj comps |> id
   let n_ratio = n1/n2
   let eye_v = extract_eyev comps
   let normal_v = extract_normalv comps
   let cos_i = dot eye_v normal_v
   let sin2_t = n_ratio * n_ratio * (1. - cos_i*cos_i)

   if t = 0.0 || sin2_t > 1.0 || remaining < 1 then
       let j2 = if logIt then
                   printfn "== Remaining %A ==" remaining
                   printfn "Reached non-transparent item id %A %A" o (t = 0.0)
                   printfn "Under total internal reflection %A" (sin2_t > 1.0)
                   printfn "out of recursion moves %A" (remaining < 1)
                   1
                else
                   1
       black
   else
       let cos_t = sqrt (1. - sin2_t)
       // Direction of the refracted ray
       let direction = normal_v * (n_ratio * cos_i - cos_t) - eye_v * n_ratio
       let under_point = extract_under_point comps
       let refract_ray = make_ray under_point direction
       let color_raw = color_at w refract_ray (remaining - 1) logIt
       let color_ans = color_raw * t
       let junk = if logIt then
                    printfn "== Remaining %A ==" remaining
                    printfn "Object id # %A" o
                    printfn "n1 %A" n1
                    printfn "n2 %A" n2
                    printfn "eyev %A" eye_v
                    printfn "normalv %A" normal_v
                    printfn "under point %A" under_point
                    printfn "n ratio %A" n_ratio
                    printfn "cos_i %A" cos_i
                    printfn "sin2_t %A" sin2_t
                    printfn "cos_t %A" cos_t
                    printfn "refract direction %A" direction
                    printfn "refracted color %A" color_ans
                    1
                  else
                    1
       color_ans



I very much appreciate any pointers. Thanks!

EDIT: I will append my prepare_computations function to here as well so that the most critical code is in one place.


let prepare_computations (i: Intersection) (r: Ray) (xs: Intersection list) (logit: bool) =
   let compute_n1n2 (hit: Intersection): double * double =
       let index_from_containers (cs: Shape list) : double option =
           match cs with
           | h::_ -> Some(extract_material h |> refractive_index)
           | [] -> Some(1.0)
       let update_containers (i: Intersection) (cs: Shape list): Shape list =
           if List.contains (object i) cs then
               let indexAt = List.findIndex (fun elem -> elem = (object i)) cs
               List.removeAt indexAt cs
           else
               (object i) :: cs
       let rec compute_aux (containers: Shape list) (intersections: Intersection list): double option * double option =
           match intersections with
           | i::is -> let opt_n1 = if i = hit then
                                       index_from_containers containers
                                   else
                                       None
                      let mod_conts = update_containers i containers
                      if i = hit then
                          let opt_n2 = index_from_containers mod_conts
                          (opt_n1, opt_n2)
                      else
                          compute_aux mod_conts is
           | _ -> failwith "Can we reach here???"
       
       match (compute_aux List.empty<Shape> xs) with
       | (Some(n1), Some(n2)) -> (n1, n2)
       | _ -> failwith "Something went wrong"
   
   let t = t_val i
   let o = object i
   let point = position r t
   let eyev = -(direction r)
   let normalv = normal_at o point
   let inside, adj_normal = if (dot normalv eyev) < 0 then (true, -normalv) else (false, normalv)
   let over_point = point + adj_normal * EPSILON
   let under_point = point - adj_normal * EPSILON
   let reflectv = reflect (direction r) normalv
   let junk = if logit then
                   printfn "In precompute"
                   printfn "Main intersection is at t = %A, object id = %A" t (id o)
                   List.map (fun x -> printfn "\tt_val %A" (t_val x)
                                      printfn "\tobj id %A" (id (object x))
                                      printfn "\tn idx %A" (refractive_index (extract_material (object x)))
                   ) xs |> ignore
                   1
              else
               1

   let (n1, n2) = compute_n1n2 i
   make_precompute t o point over_point under_point eyev adj_normal reflectv n1 n2 inside

The compute_n1n2 is a little wonky since I am trying to do this in a purely functional manner, but it passes all the tests as I would expect.

Jamis, sure thing, I am building them based off the YAML (or my interpretation of it from the previous page)


   let checkers   = make_pattern (Checkers(Color(0.15,0.15,0.15), Color(0.85,0.85,0.85)))
   let floor_material = make_material [checkers] 0.8 0.2 0.0 0.0 0.0 0.0 1.0
   let floor      = make_shape Plane
                    |> set_shape_transform (chain [rotation_x halfPi; translation 0 0 10])
                    |> set_shape_material floor_material

   
   let glass_ball = make_shape Sphere
                    |> set_shape_material (make_material (solid_pattern white) 0 0 0.9 300 0.9 0.9 1.5)

   let air_bubble = make_shape Sphere
                    |> set_shape_material (make_material (solid_pattern white) 0 0 0.9 300 0.9 0.9 1.0000034)
                    |> set_shape_transform (scaling 0.5 0.5 0.5)

   let ls = make_pointlight (make_point 2 10 -5) (Color(0.9, 0.9, 0.9))
   let world = make_world [ls] [floor; glass_ball; air_bubble]//;back_wall; side_wall; middle]
   let camera = make_camera 300 300 0.45 |> set_camera_transform (view_transform (make_point 0 0 -5)
                                                                                 (make_point 0 0 0)
                                                                                 (make_vector 0 1 0))

Here, the arguments to make_material are: pattern, ambient, diffuse, specular, shininess, reflective, transparency, and refractive_index

EDIT: And here is a link to a higher resolution rendering of the same scene (800x800) (imgur link).  I would have expected it to look like auctux's on the top of this page.  Zooming in, and the effect of "looking through the glass make it look like a low res image" seems really clear to me as I have no better explanation for it.  Not, I have NOT implemented the Fresnel effect yet, that was for tonight, but I got tripped up with the "regular" version.  Thanks again