Support searching for the raylib library on multiple paths. (#34)

Add a new environment variable "USE_EXTERNAL_RAYLIB" which will
alter the load behaviour to not include a directory prefix. This
lets us fallback onto the system library loading mechanism.
Remove specific raylib library filenames.
This ability is important for operating systems like Nix.

README.md

@@ -28,6 +28,9 @@ If yours isn't available then pip will attempt to build from source, so you will
 
 See here for a Raspberry Pi build: https://github.com/electronstudio/raylib-python-cffi/issues/31#issuecomment-862078330
 
+If your system already has the Raylib library installed, you can set the environment variable 'USE_EXTERNAL_RAYLIB' and it will
+be used instead.
+
 ## Option 2: Build from source
 
 If you're using a platform we don't have binary builds for yet
@@ -61,7 +64,7 @@ Build and install Raylib from the raylib-c directory.
     cd ..\..
 
 To update the dynamic libs, download the official release, e.g. https://github.com/raysan5/raylib/releases/download/3.7.0/raylib-3.7.0_win64_msvc16.zip and extract `raylib.dll`
-into `raylib/dynamic`.  Delete the files for other platforms, unless you want them in your distribution. 
+into `raylib/dynamic`.  Delete the files for other platforms, unless you want them in your distribution.
 
 To build a binary wheel distribution:
 
@@ -73,7 +76,7 @@ To build a binary wheel distribution:
 and install it:
 
     pip3 install dist\raylib-3.7.0-cp37-cp37m-win_amd64.whl
-    
+
 (Note: your wheel's filename will probably be different than the one here.)
 
 ### Linux etc
@@ -100,13 +103,13 @@ Optional: Make a patched version of raylib header.  (Not necessary if you've alr
     patch  -p0 <raylib_modified.h.patch
 
 
-Build 
+Build
 
     pip3 install cffi
     cd ..
     rm -rf build raylib/static/_raylib_cffi.*
     python3 raylib/static/build.py
-    
+
 
 To update the Linux dynamic libs (names will be different on other platfroms):
 
@@ -261,4 +264,3 @@ You can create a standalone binary using the Nuitka compiler.  For example, here
     pip3 install nuitka
     cd examples/textures
     python3 -m nuitka --onefile --linux-onefile-icon resources/wabbit_alpha.png textures_bunnymark.py
-

raylib/dynamic/__init__.py

@@ -3,35 +3,41 @@ This is an attempt at a CFFI dynamic (ABI) binding.  It was failing in the exact
 materials of a model.  But now it __seems__ to work
 """
 
+from cffi import FFI
+import itertools
+import os
+import pathlib
 import platform
 
-# Probably unnecessary, just covering all bases in case people add or remove dlls
-MAC_NAMES = ['libraylib.3.5.0.dylib', 'libraylib.301.dylib', 'libraylib.dylib']
-LINUX_NAMES = ['libraylib.so.3.5.0','libraylib.so.3', 'libraylib.so']
-WINDOWS_NAMES = ['libraylib.dll', 'raylib.dll','32bit/raylib.dll',  '32bit/libraylib.dll']
-
-if platform.system() == "Darwin":
-    NAMES_TO_TRY = MAC_NAMES
-elif platform.system() == "Linux":
-    NAMES_TO_TRY = LINUX_NAMES
-elif platform.system() == "Windows":
-    NAMES_TO_TRY = WINDOWS_NAMES
-else:
-    NAMES_TO_TRY = MAC_NAMES + LINUX_NAMES + WINDOWS_NAMES
-
-import pathlib
 MODULE = pathlib.Path(__file__).parent.parent
 
-from cffi import FFI
+def raylib_library_path():
+    '''Return the full path of the raylib shared library
+    If the environment variable "USE_EXTERNAL_RAYLIB" is set (no value required)
+    then the library will be loaded from the system library paths.
+    '''
+    def so_path():
+        return str(MODULE / 'dynamic') if not 'USE_EXTERNAL_RAYLIB' in os.environ else ''
+    def so_name():
+        '''Returns the appropriate for the library on the current platform.'''
+        lib_filenames = {
+            'Windows': 'libraylib.dll',
+            'Linux': 'libraylib.so',
+            'Darwin': 'libraylib.dylib',
+        }
+        if platform.system() not in lib_filenames:
+            raise ValueError('Unrecognised system "{}"'.format(platform.system()))
+        return lib_filenames.get(platform.system())
+
+    return os.path.join(so_path(), so_name())
+
+
 ffi = FFI()
 ffi.cdef(open(MODULE / "raylib_modified.h").read().replace('RLAPI ', ''))
 
-for name in NAMES_TO_TRY:
+try:
-    file = str(MODULE)+"/dynamic/"+name
+    raylib_fname = raylib_library_path()
-    try:
+    raylib = ffi.dlopen(raylib_fname)
-        raylib = ffi.dlopen(file)
+    print('LOADED DYNAMICALLY SHARED LIB "{}"'.format(raylib_fname))
-        print("LOADED DYNAMICALLY SHARED LIB "+file)
+except Exception as e:
-        break
+    print(e)
-    except Exception as e:
-        print(e)
-