#!/usr/bin/env python

header    = 'Penang Island terrain 3D model based on ASTER Global DEM data by CMG Lee.'
path_dem  = 'Penang_Island_heightmap_ASTGTM2_N05E100_dem_20pc.png'
scale     = 5e-2
thickness = 1

import re, struct, math, png
def fmt(string): ## string.format(**vars()) using tags {expression!format} by CMG Lee
 def f(tag): i_sep = tag.rfind('!'); return (re.sub('\.0+$', '', str(eval(tag[1:-1])))
  if (i_sep < 0) else ('{:%s}' % tag[i_sep + 1:-1]).format(eval(tag[1:i_sep])))
 return (re.sub(r'(?<!{){[^{}]+}', lambda m:f(m.group()), string)
         .replace('{{', '{').replace('}}', '}'))
def append(obj, string): return obj.append(fmt(string))
def tabbify(cellss, separator='|'):
 cellpadss = [list(rows) + [''] * (len(max(cellss, key=len)) - len(rows)) for rows in cellss]
 fmts = ['%%%ds' % (max([len(str(cell)) for cell in cols])) for cols in zip(*cellpadss)]
 return '\n'.join([separator.join(fmts) % tuple(rows) for rows in cellpadss])
def hex_rgb(colour): ## convert [#]RGB to #RRGGBB and [#]RRGGBB to #RRGGBB
 return '#%s' % (colour if len(colour) > 4 else ''.join([c * 2 for c in colour])).lstrip('#')
def viscam_colour(colour):
 colour_hex      = hex_rgb(colour)
 colour_top5bits = [int(colour_hex[i:i+2], 16) >> 3 for i in range(1,7,2)]
 return (1 << 15) + (colour_top5bits[0] << 10) + (colour_top5bits[1] << 5) + colour_top5bits[2]
def roundm(x, multiple=1):
 if   (isinstance(x, tuple)): return tuple(roundm(list(x), multiple))
 elif (isinstance(x, list )): return [roundm(x_i, multiple) for x_i in x]
 else: return int(math.floor(float(x) / multiple + 0.5)) * multiple
def flatten(lss): return [l for ls in lss for l in ls]
def rotate(facetss, degs): ## around x then y then z axes
 (deg_x,deg_y,deg_z) = degs
 (sin_x,cos_x) = (math.sin(math.radians(deg_x)), math.cos(math.radians(deg_x)))
 (sin_y,cos_y) = (math.sin(math.radians(deg_y)), math.cos(math.radians(deg_y)))
 (sin_z,cos_z) = (math.sin(math.radians(deg_z)), math.cos(math.radians(deg_z)))
 facet_rotatess = []
 for facets in facetss:
  facet_rotates = []
  for i_point in range(4):
   (x, y, z) = [facets[3 * i_point + i_xyz] for i_xyz in range(3)]
   if (x is None or y is None or z is None):
    facet_rotates += [x, y, z]
   else:
    (y, z) = (y * cos_x - z * sin_x,  y * sin_x + z * cos_x) ## rotate about x
    (x, z) = (x * cos_y + z * sin_y, -x * sin_y + z * cos_y) ## rotate about y
    (x, y) = (x * cos_z - y * sin_z,  x * sin_z + y * cos_z) ## rotate about z
    facet_rotates += [round(value, 9) for value in [x, y, z]]
  facet_rotatess.append(facet_rotates)
 return facet_rotatess
def translate(facetss, ds): ## ds = (dx,dy,dz)
 return [facets[:3] + [facets[3 * i_point + i_xyz] + ds[i_xyz]
                       for i_point in range(1,4) for i_xyz in range(3)]
         for facets in facetss]

## Read elevation data
(map_width, map_height, map_pixels, map_metadatas) = png.Reader(path_dem).read_flat()
print(map_width, map_height, len(map_pixels), map_metadatas)
heightss = [[map_pixels[4 * (map_width * y + x) + 1]
             for y in range(map_height)] for x in range(map_width)]

## Add facets
facetss = []
for y in range(map_height - 1):
 for x in range(map_width - 1):
  (x0, y0, x1, y1) = (x, -y, x + 1, -(y + 1))
  z00 = heightss[x    ][y    ] * scale
  z01 = heightss[x    ][y + 1] * scale
  z11 = heightss[x + 1][y + 1] * scale
  z10 = heightss[x + 1][y    ] * scale
  if (abs(z00 - z11) < abs(z01 - z10)):
   if (z11 != 0 or z10 != 0 or z00 != 0):
    facetss.append([None,0,0,  x1,y1,z11,  x1,y0,z10,  x0,y0,z00])
   if (z00 != 0 or z01 != 0 or z11 != 0):
    facetss.append([None,0,0,  x0,y0,z00,  x0,y1,z01,  x1,y1,z11])
  else:
   if (z10 != 0 or z00 != 0 or z01 != 0):
    facetss.append([None,0,0,  x1,y0,z10,  x0,y0,z00,  x0,y1,z01])
   if (z01 != 0 or z11 != 0 or z10 != 0):
    facetss.append([None,0,0,  x0,y1,z01,  x1,y1,z11,  x1,y0,z10])
  # sys.stdout.write(chr(int(math.ceil(heightss[x][y] * 0.1)) + 32))
 # print('')
# writer = png.Writer(width=map_width, height=map_height, alpha=map_metadatas['alpha'])
# writer.write_array(open('test.png', 'wb'), map_pixels)
facetss += [facets[0: 5] + [max(0, facets[ 5] - thickness)] +
            facets[9:11] + [max(0, facets[11] - thickness)] +
            facets[6: 8] + [max(0, facets[ 8] - thickness)] for facets in facetss]
# facetss = [facets[:3] + facets[6:9] + facets[3:6] + facets[9:] for facets in facetss] ## flip

## Calculate normals
for facets in facetss:
 if (facets[0] is None or facets[1] is None or facets[2] is None):
  us      = [facets[i_xyz + 9] - facets[i_xyz + 6] for i_xyz in range(3)]
  vs      = [facets[i_xyz + 6] - facets[i_xyz + 3] for i_xyz in range(3)]
  normals = [us[1]*vs[2] - us[2]*vs[1], us[2]*vs[0] - us[0]*vs[2], us[0]*vs[1] - us[1]*vs[0]]
  normal_length = sum([component * component for component in normals]) ** 0.5
  facets[:3] = [-round(component / normal_length, 10) for component in normals]

# print(tabbify([['N%s'  % (xyz   )                   for xyz in list('xyz')] +
#                ['%s%d' % (xyz, n) for n in range(3) for xyz in list('XYZ')] + ['RGB']] + facetss))
## Compile STL
outss = ([[('STL\n\n%-73s\n\n' % (header[:73])).encode('utf-8'), struct.pack('<L',len(facetss))]] +
         [[struct.pack('<f',float(value)) for value in facets[:12]] +
          [struct.pack('<H',0 if (len(facets) <= 12) else
                            viscam_colour(facets[12]))] for facets in facetss])
out   = b''.join([bytes(out) for outs in outss for out in outs])
# out += ('\n\n## Python script to generate STL\n\n%s\n' % (open(__file__).read())).encode('utf-8')
print("# bytes:%d\t# facets:%d\ttitle:\"%-73s\"" % (len(out), len(facetss), header[:73]))
with open(__file__[:__file__.rfind('.')] + '.stl', 'wb') as f_out: f_out.write(out)