'2d simplex noise

global simx_f2
global simx_g2
dim global simx_perm(511),simp_gx(7),simp_gy(7)

simx_perm_data:
data 151,160,137,91,90,15,131,13
data 201,95,96,53,194,233,7,225
data 140,36,103,30,69,142,8,99
data 37,240,21,10,23,190,6,148
data 247,120,234,75,0,26,197,62
data 94,252,219,203,117,35,11,32
data 57,177,33,88,237,149,56,87
data 174,20,125,136,171,168,68,175
data 74,165,71,134,139,48,27,166
data 77,146,158,231,83,111,229,122
data 60,211,133,230,220,105,92,41
data 55,46,245,40,244,102,143,54
data 65,25,63,161,1,216,80,73
data 209,76,132,187,208,89,18,169
data 200,196,135,130,116,188,159,86
data 164,100,109,198,173,186,3,64
data 52,217,226,250,124,123,5,202
data 38,147,118,126,255,82,85,212
data 207,206,59,227,47,16,58,17
data 182,189,28,42,223,183,170,213
data 119,248,152,2,44,154,163,70
data 221,153,101,155,167,43,172,9
data 129,22,39,253,19,98,108,110
data 79,113,224,232,178,185,112,104
data 218,246,97,228,251,34,242,193,238
data 210,144,12,191,179,162,241
data 81,51,145,235,249,14,239,107
data 49,192,214,31,181,199,106,157
data 184,84,204,176,115,121,50,45
data 127,4,150,254,138,236,205,93
data 222,114,67,29,24,72,243,141
data 128,195,78,66,215,61,156,180
simp_grad:
data 1,1, -1,1, 1,-1, -1,-1
data 1,0, -1,0, 0,1, 0,-1

simx_f2=0.5*(sqr(3)-1)
simx_g2=(3-sqr(3))/6

restore simx_perm_data
for i=0 to 255
  read v
  simx_perm(i)=v
  'doubled to avoid index wrap
  simx_perm(i+256)=v
next i

restore simp_grad
for i=0 to 7
  read simp_gx(i),simp_gy(i)
next i

sub noise2d(xin,yin,result)
  'skew input space to the simplex grid
  s=(xin+yin)*simx_f2
  i=floor(xin+s)
  j=floor(yin+s)
  t=(i+j)*simx_g2
  'distance from cell origin, unskewed
  x0=xin-(i-t)
  y0=yin-(j-t)

  'which of the two triangles are we in?
  if x0>y0 then
    i1=1
    j1=0
  else
    i1=0
    j1=1
  end if

  'offsets for the other two corners
  x1=x0-i1+simx_g2
  y1=y0-j1+simx_g2
  x2=x0-1+2*simx_g2
  y2=y0-1+2*simx_g2

  'hashed gradient indices (and 255 wraps, and 7 picks a gradient)
  ii=i and 255
  jj=j and 255
  gi0=simx_perm(ii   +simx_perm(jj   )) and 7
  gi1=simx_perm(ii+i1+simx_perm(jj+j1)) and 7
  gi2=simx_perm(ii+1 +simx_perm(jj+1 )) and 7

  n0=0 :n1=0 :n2=0

  'corner 0 contribution
  t0=0.5-x0*x0-y0*y0
  if t0>0 then
    t0=t0*t0
    n0=t0*t0*(simp_gx(gi0)*x0+simp_gy(gi0)*y0)
  end if

  'corner 1
  t1=0.5-x1*x1-y1*y1
  if t1>0 then
    t1=t1*t1
    n1=t1*t1*(simp_gx(gi1)*x1+simp_gy(gi1)*y1)
  end if

  'corner 2
  t2=0.5-x2*x2-y2*y2
  if t2>0 then
    t2=t2*t2
    n2=t2*t2*(simp_gx(gi2)*x2+simp_gy(gi2)*y2)
  end if

  'scale to roughly -1..1
  result=70*(n0+n1+n2)
end sub









'user's function that actually draw cells of the world
'(in) l,t = left and top position in world-cell-coords
'(in) (w,h) = with and height dimension in world-cell-coords
'it will ask to draw horizontal or vertical lines from the world
sub inf_world(l,t,w,h)
  bg 3
  
  'another idea is to generate on the fly what to draw
  'here using a simplex noise generator
  n=0
  if w>h then
    'drawing an horizontal line
    for x=0 to w-1
      call noise2d((l+x)*0.11,t*0.11,n)
      p=floor((n+1)*0.5*6)
      p=clamp(p,0,6)
      pal p
      cell l+x,t,1
    next x
  else if w<h then
    'drawing a vertical line
    for y=0 to h-1
      call noise2d(l*0.11,(t+y)*0.11,n)
      p=floor((n+1)*0.5*6)
      p=clamp(p,0,6)
      pal p
      cell l,t+y,1
    next y
  end if
end sub

'user's function to scroll the background
sub inf_scroll(x,y)
  scroll 3,x,y
end sub

'rectangle of the whole world map
'a.k.a.: world boundaries in world-cell-coords
infl=0
inft=0
infr=102 :'3
infb=102 :'3

'camera dimension, a.k.a.: view dimension in pixel-coords
'camera view start of the top-left corner of the device, if you want to change it, do it yourself.
infw=shown.w
infh=shown.h

'world cell size in pixel-coord, a.k.a.: pixel to cell conversion
infs=8

'number of cells to draw out of the view to make then already drawn when the camera is panned.
'note if the number is too big it can lead to overwrite wrapped cells the are visible.
'max value=7 with infs=8
infco=3

'compute space occupied by the whole world in pixel-coords
infpw=(infr-infl+1)*infs
infph=(infb-inft+1)*infs

'camera position in the world in pixel-coords
'initial position point to the center of the world
infx=-(infw-infpw)/2
infy=-(infh-infph)/2

gosub inf_prepare

'rectangle of what portion of the world is currently drawn
'a.k.a.: view drawing cursor in world-cell-coords
'initial rectangle start from the center of the view
infcl=(infpl+infpr)\2
infct=(infpt+infpb)\2
infcr=infcl-1
infcb=infct-1

font 0

'need recompute position
infnl=-1
do
  if tap then
    'save original pan position of the world
    infxs=infx
    infys=infy
  else if touch then
    'pan the camera view onto the world
    infx=infxs-(touch.x-touch.px)
    infy=infys-(touch.y-touch.py)
    infnl=-1
  end if

  if infnl then gosub inf_position

  gosub inf_draw
  'if you want to draw faster
  gosub inf_draw
  gosub inf_draw
  
  bg 0
  pal 0
  number 3,3,infpl,4
  number 3,4,infpt,4
  number 3,5,infpr,4
  number 3,6,infpb,4

  wait vbl
loop

'make sure the camera position allow to see the world and some of the out-of-bound characters around it.
inf_position:
  infnl=0

  'in x axis
  if infpw>infw then
    'world is bigger than the view
    l=infl*infs
    r=(infr+1)*infs-infw
    'prevent to past beyond
    if infx<l then infx=l
    if infx>r then infx=r
  else
    'world is small than the view, center it
    infx=-(infw-infpw)/2
  end if
  'in y axis
  if infph>infh then
    'world is bigger than the view
    t=inft*infs
    b=(infb+1)*infs-infh
    if infy<t then infy=t
    if infy>b then infy=b
  else
    'world is small than the view, center it
    infy=-(infh-infph)/2
  end if
  call inf_scroll(infx,infy)
  goto inf_prepare

inf_prepare:
  'rectangle of the view, the portion of the visible world
  'a.k.a.: view position in world-cell-coords
  infpl=int(infx/infs)-infco
  infpt=int(infy/infs)-infco
  infpr=int((infx+infw)/infs)+infco
  infpb=int((infy+infh)/infs)+infco
  return

inf_draw:

  'render missing world cells at left
  if infpl<infcl and infcl>infl then
    dec infcl
    if infcr-infcl>=64 then dec infcr
    call inf_world(infcl,infct,1,infcb-infct+1)
  end if
  
  'render missing cells at right
  if infpr>infcr and infcr<infr then
    inc infcr
    if infcr-infcl>=64 then inc infcl
    call inf_world(infcr,infct,1,infcb-infct+1)
  end if
  
  'render missing cells at top
  if infpt<infct and infct>inft then
    dec infct
    if infcb-infct>=64 then dec infcb
    call inf_world(infcl,infct,infcr-infcl+1,1)
  end if
  
  'render missing cells at bottom
  if infpb>infcb and infcb<infb then
    inc infcb
    if infcb-infct>=64 then inc infct
    call inf_world(infcl,infcb,infcr-infcl+1,1)
  end if
  
  return

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