Tunnel 3D

#!/usr/bin/env gmic
# File : tunnel3d.gmic
# Author : David Tschumperle

# Entrypoint when run from CLI:
go =>[^] "Tunnel 3D" e[] "" animate 30

# Main function
go :
  v 0

  # Generate template mesh for the 3D tunnel.
  curve3d 0,0,t,1,64,0,63,16,0 rv3d # Generate a straight bar along z-axis
  s3d eval "i[#1,1]-=32" rows... 0,{-3,h-4*32-1} rows.. 0,{-2,h-3*32-1} rows. 0,{h-32-1} a y # Remove closed extremities
  2,1024,1,3,"x?[255,200,128]:[255,0,0]"
  (0^0^0;0.25^0.25^1;1^1^1;0^0^0)
  2,{-2,h},1,3,"Y = lerp(0,h#-1,(y/h)^0.5); cut(I(#-1,0,Y,0,2),0,1)" rm.. *[-2,-1] # Colors for depth shading

  t3d.. . rm. . => template3d,mesh3d
  +l. { s3d off_p:=8+{2,h} k... r 13,{h/13},1,1,-1 permute zycx } => primitives # Keep editable version of primitives

  # Generate sequence of 3D tunnel centers.
  1,48,1,2,g b. y,4,2 n. -1.5,2 a. .,y => coords
  +g. y b. 1,2 channels. 0,2 sh. 100% f. 1 rm. orientation. => orientations # Desired camera orientations

  # Display animation
  nbf=256 mzi2=-inf
  repeat $nbf { f=$>
    e[] "\r  > Frame "{$f+1}"/"$nbf

    z:=16+lerp(0,h#$coords/2,$>/$nbf)
    zi2:=2*int($z/2)
    if $zi2!=$mzi2 # Generate 3D mesh for current tunnel view.
      +z[template3d] 0,8,0,{template3d,8+3*i[6]-1} r. 3,{h/3},1,1,-1 permute. zycx # Extract 3D coordinates
      f. "C = I[#$coords,$zi2 + i2,2]; [ i0 + C[0],i1 + C[1],i2 ]"
      permute. cyzx y. +j[template3d] .,0,8,0,0 rm..
      mzi2:=$zi2
      j[mesh3d] . rm.
    fi

    cx,cy:="I(#$coords,0,$z,0,2,2)"
    u,v,w:="unitnorm(I(#$orientations,0,$z,0,2,2))"
    M:="W = unitnorm(I(#$orientations,0,$z,0,2,2)); V = cross(W,[1,0,0]); U = cross(V,W); 1.5*[ U,V,W ]" # Camera matrix

    +-3d[mesh3d] $cx,$cy,{$z%2}
    apply_matrix3d. $M
    r3d. 0,0,1,{180*cos(2*pi*$>/$nbf)}

    # Add depth effect.
    f[primitives] "
      P = I;
      z = int(y/16);
      P[5] = P[7] = P[9] = P[11] = xor(z,y)%2;
      P[6] = 16*i[#-1,8+3*i1+2];
      P[8] = 16*i[#-1,8+3*i2+2];
      P[10] = 16*i[#-1,8+3*i3+2];
      P[12] = 16*i[#-1,8+3*i4+2];
      P"
    +permute[primitives] cyzx y. j.. .,0,$off_p rm.

    # Render frame.
    600,600,1,3
    j3d. ..,50%,50%,-500,1,2,0,0,500 rm..
  }
  k[5--1] rs 320 a z n 0,255 s z round

# End of file.