webapp/django/contrib/gis/gdal/prototypes/generation.py

"""
 This module contains functions that generate ctypes prototypes for the
 GDAL routines.
"""

from ctypes import c_char_p, c_double, c_int, c_void_p
from django.contrib.gis.gdal.prototypes.errcheck import \
    check_arg_errcode, check_errcode, check_geom, check_geom_offset, \
    check_pointer, check_srs, check_str_arg, check_string, check_const_string

def double_output(func, argtypes, errcheck=False, strarg=False):
    "Generates a ctypes function that returns a double value."
    func.argtypes = argtypes
    func.restype = c_double
    if errcheck: func.errcheck = check_arg_errcode
    if strarg: func.errcheck = check_str_arg
    return func

def geom_output(func, argtypes, offset=None):
    """
    Generates a function that returns a Geometry either by reference
    or directly (if the return_geom keyword is set to True).
    """
    # Setting the argument types
    func.argtypes = argtypes

    if not offset:
        # When a geometry pointer is directly returned.
        func.restype = c_void_p
        func.errcheck = check_geom
    else:
        # Error code returned, geometry is returned by-reference.
        func.restype = c_int
        def geomerrcheck(result, func, cargs):
            return check_geom_offset(result, func, cargs, offset)
        func.errcheck = geomerrcheck

    return func

def int_output(func, argtypes):
    "Generates a ctypes function that returns an integer value."
    func.argtypes = argtypes
    func.restype = c_int
    return func

def srs_output(func, argtypes):
    """
    Generates a ctypes prototype for the given function with
    the given C arguments that returns a pointer to an OGR
    Spatial Reference System.
    """
    func.argtypes = argtypes
    func.restype = c_void_p
    func.errcheck = check_srs
    return func

def const_string_output(func, argtypes, offset=None):
    func.argtypes = argtypes
    if offset:
        func.restype = c_int
    else:
        func.restype = c_char_p

    def _check_const(result, func, cargs):
        return check_const_string(result, func, cargs, offset=offset)
    func.errcheck = _check_const

    return func

def string_output(func, argtypes, offset=-1, str_result=False):
    """
    Generates a ctypes prototype for the given function with the
    given argument types that returns a string from a GDAL pointer.
    The `const` flag indicates whether the allocated pointer should 
    be freed via the GDAL library routine VSIFree -- but only applies
    only when `str_result` is True.
    """
    func.argtypes = argtypes
    if str_result:
        # String is the result, don't explicitly define
        # the argument type so we can get the pointer.
        pass
    else:
        # Error code is returned
        func.restype = c_int

    # Dynamically defining our error-checking function with the
    # given offset.
    def _check_str(result, func, cargs):
        return check_string(result, func, cargs,
                            offset=offset, str_result=str_result)
    func.errcheck = _check_str
    return func

def void_output(func, argtypes, errcheck=True):
    """
    For functions that don't only return an error code that needs to
    be examined.
    """
    if argtypes: func.argtypes = argtypes
    if errcheck:
        # `errcheck` keyword may be set to False for routines that
        # return void, rather than a status code.
        func.restype = c_int
        func.errcheck = check_errcode
    else:
        func.restype = None
        
    return func

def voidptr_output(func, argtypes):
    "For functions that return c_void_p."
    func.argtypes = argtypes
    func.restype = c_void_p
    func.errcheck = check_pointer
    return func