# Source code for fontTools.varLib.interpolate_layout

    """
    Interpolate OpenType Layout tables (GDEF / GPOS / GSUB).
    """
    from fontTools.ttLib import TTFont
    from fontTools.varLib import models, VarLibError, load_designspace, load_masters
    from fontTools.varLib.merger import InstancerMerger
    import os.path
    import logging
    from copy import deepcopy
    from pprint import pformat

    log = logging.getLogger("fontTools.varLib.interpolate_layout")

    def interpolate_layout(designspace, loc, master_finder=lambda s:s, mapped=False):
    	"""
    	Interpolate GPOS from a designspace file and location.

    	If master_finder is set, it should be a callable that takes master
    	filename as found in designspace file and map it to master font
    	binary as to be opened (eg. .ttf or .otf).

    	If mapped is False (default), then location is mapped using the
    	map element of the axes in designspace file.  If mapped is True,
    	it is assumed that location is in designspace's internal space and
    	no mapping is performed.
    	"""
    	if hasattr(designspace, "sources"):  # Assume a DesignspaceDocument
    		pass
    	else:  # Assume a file path
    		from fontTools.designspaceLib import DesignSpaceDocument
    		designspace = DesignSpaceDocument.fromfile(designspace)

    	ds = load_designspace(designspace)
    	log.info("Building interpolated font")

    	log.info("Loading master fonts")
    	master_fonts = load_masters(designspace, master_finder)
    	font = deepcopy(master_fonts[ds.base_idx])

    	log.info("Location: %s", pformat(loc))
    	if not mapped:
    		loc = {name: ds.axes[name].map_forward(v) for name,v in loc.items()}
    	log.info("Internal location: %s", pformat(loc))
    	loc = models.normalizeLocation(loc, ds.internal_axis_supports)
    	log.info("Normalized location: %s", pformat(loc))

    	# Assume single-model for now.
    	model = models.VariationModel(ds.normalized_master_locs)
    	assert 0 == model.mapping[ds.base_idx]

    	merger = InstancerMerger(font, model, loc)

    	log.info("Building interpolated tables")
    	# TODO GSUB/GDEF
    	merger.mergeTables(font, master_fonts, ['GPOS'])
    	return font

    def main(args=None):
    	"""Interpolate GDEF/GPOS/GSUB tables for a point on a designspace"""
    	from fontTools import configLogger
    	import argparse
    	import sys

    	parser = argparse.ArgumentParser(
    		"fonttools varLib.interpolate_layout",
    		description=main.__doc__,
    	)
    	parser.add_argument('designspace_filename', metavar='DESIGNSPACE',
    		help="Input TTF files")
    	parser.add_argument('locations', metavar='LOCATION', type=str, nargs='+',
    		help="Axis locations (e.g. wdth=120")
    	parser.add_argument('-o', '--output', metavar='OUTPUT',
    		help="Output font file (defaults to <designspacename>-instance.ttf)")
    	parser.add_argument('-l', '--loglevel', metavar='LEVEL', default="INFO",
    		help="Logging level (defaults to INFO)")

    	args = parser.parse_args(args)

    	if not args.output:
    		args.output = os.path.splitext(args.designspace_filename)[0] + '-instance.ttf'

    	configLogger(level=args.loglevel)

    	finder = lambda s: s.replace('master_ufo', 'master_ttf_interpolatable').replace('.ufo', '.ttf')

    	loc = {}
    	for arg in args.locations:
    		tag,val = arg.split('=')
    		loc[tag] = float(val)

    	font = interpolate_layout(args.designspace_filename, loc, finder)
    	log.info("Saving font %s", args.output)
    	font.save(args.output)

    if __name__ == "__main__":
    	import sys
    	if len(sys.argv) > 1:
    		sys.exit(main())
    	import doctest
    	sys.exit(doctest.testmod().failed)