4 ms·

Can anybody provide de-obfuscated/minified source so those of us who understand the principle (tracing rays of light around a scene) can understand the maths?

kragen 3y ago
here's my attempt 10 REMĀĘĆĞ$Č*Ēĉ!ăě-ĕ'ď rem dithering table in comment above consulted by GCOL line? rem raytracer from https://bbcmic.ro/?t=9ctpk by https://mastodon.me.uk/@coprolite9000 rem deobfuscated and possibly broken by kragen javier sitaker (untested) 20 MODE 1 VDU 5 30 FOR N = 8 TO 247 : rem loop over rows (n) and columns (m) of pixels FOR M = 0 TO 319 40 X = 0 : rem three-dimensional vector Y = -.1 Z = 3 U = (M - 159.5)/160 : rem xform screen coords to direction vector V = (N - 127.5)/160 W = 1/SQR(U*U + V*V + 1) : rem normalize direction vector U = U * W V = V * W I = SGN U : rem derive coordinate of sphere center (i, i, 1)? G = 1 50 E = X - I : rem beginning of do-while loop F = Y - I P = U*E + V*F - W*Z D = P*P - E*E - F*F - Z*Z + 1 IF D <= 0 then goto 60 T = -P - SQR D IF T <= 0 then goto 60 X = X + T*U Y = Y + T*V Z = Z - T*W E = X - I F = Y - I G = Z P = 2*(U*E + V*F - W*G) U = U - P*E V = V - P*F W = W + P*G I = -I : rem if we are reflecting then check other sphere now GOTO 50 : rem end of do-while loop, we have our escape from the scene geometry rem color according to y-component of direction vector to get sky gradient rem if instead y component is negative, make a checkerboard of pieces of sky 60 IF V < 0 then P = (Y + 2)/V : V = -V*((INT(X - U*P) + INT(Z - W*P) AND 1)/2 + .3) + .2 70 GCOL 0, 3 - (48*SQR V + ?(PAGE + 5 + M MOD 4 + N MOD 4*4)/3) DIV 16 80 PLOT 69, 4*M, 4*N NEXT, i'm interested to hear what i got wrong see also https://news.ycombinator.com/item?id=39026517 https://news.ycombinator.com/item?id=39026517 and https://news.ycombinator.com/item?id=39026495 https://news.ycombinator.com/item?id=39026495
- Sharlin 3y ago
  > rem if instead y component is negative, make a checkerboard of pieces of sky I'd maybe phrase this a bit differently – in both cases it uses the v coordinate to calculate the shade but whereas the sky is a simple gradient, the plane has a "ground fog" type effect that can be adjusted with those +.3 and +.2 magic constants.
  - kragen 3y ago
    i was trying to figure out how the ground fog happens, and i still don't
    - Sharlin 3y ago
      The value of v corresponds to how far away the intersection point is. At the horizon v=0 so the color value is just constant 0.2. The closer to the camera, the more the checker value (0 or 1) contributes. The exact values are probably chosen experimentally, but note the important property that -v*(checker/2+0.3)+0.2 is always between 0 and 1. Note also that 1 means black and 0 white here, as ultimately the value is negated at line 70.

kragen 3y ago

here's my attempt 10 REMĀĘĆĞ$Č*Ēĉ!ăě-ĕ'ď rem dithering table in comment above consulted by GCOL line? rem raytracer from https://bbcmic.ro/?t=9ctpk by https://mastodon.me.uk/@coprolite9000 rem deobfuscated and possibly broken by kragen javier sitaker (untested) 20 MODE 1 VDU 5 30 FOR N = 8 TO 247 : rem loop over rows (n) and columns (m) of pixels FOR M = 0 TO 319 40 X = 0 : rem three-dimensional vector Y = -.1 Z = 3 U = (M - 159.5)/160 : rem xform screen coords to direction vector V = (N - 127.5)/160 W = 1/SQR(U*U + V*V + 1) : rem normalize direction vector U = U * W V = V * W I = SGN U : rem derive coordinate of sphere center (i, i, 1)? G = 1 50 E = X - I : rem beginning of do-while loop F = Y - I P = U*E + V*F - W*Z D = P*P - E*E - F*F - Z*Z + 1 IF D <= 0 then goto 60 T = -P - SQR D IF T <= 0 then goto 60 X = X + T*U Y = Y + T*V Z = Z - T*W E = X - I F = Y - I G = Z P = 2*(U*E + V*F - W*G) U = U - P*E V = V - P*F W = W + P*G I = -I : rem if we are reflecting then check other sphere now GOTO 50 : rem end of do-while loop, we have our escape from the scene geometry rem color according to y-component of direction vector to get sky gradient rem if instead y component is negative, make a checkerboard of pieces of sky 60 IF V < 0 then P = (Y + 2)/V : V = -V*((INT(X - U*P) + INT(Z - W*P) AND 1)/2 + .3) + .2 70 GCOL 0, 3 - (48*SQR V + ?(PAGE + 5 + M MOD 4 + N MOD 4*4)/3) DIV 16 80 PLOT 69, 4*M, 4*N NEXT, i'm interested to hear what i got wrong see also https://news.ycombinator.com/item?id=39026517 https://news.ycombinator.com/item?id=39026517 and https://news.ycombinator.com/item?id=39026495 https://news.ycombinator.com/item?id=39026495

Sharlin 3y ago
> rem if instead y component is negative, make a checkerboard of pieces of sky I'd maybe phrase this a bit differently – in both cases it uses the v coordinate to calculate the shade but whereas the sky is a simple gradient, the plane has a "ground fog" type effect that can be adjusted with those +.3 and +.2 magic constants.
- kragen 3y ago
  i was trying to figure out how the ground fog happens, and i still don't
  - Sharlin 3y ago
    The value of v corresponds to how far away the intersection point is. At the horizon v=0 so the color value is just constant 0.2. The closer to the camera, the more the checker value (0 or 1) contributes. The exact values are probably chosen experimentally, but note the important property that -v*(checker/2+0.3)+0.2 is always between 0 and 1. Note also that 1 means black and 0 white here, as ultimately the value is negated at line 70.