Adding enforcement of the wanted graphics system GL/GLES

- GRAPHICS=GL/GLES

setup.py

@@ -74,6 +74,15 @@ c_options['use_x11'] = False
 c_options['use_gstreamer'] = False
 c_options['use_avfoundation'] = platform == 'darwin'
 
+if environ.get('GRAPHICS') is not None:
+    print('\nForcing to use this graphics system: %s' %repr(environ.get('GRAPHICS')))
+    if   environ.get('GRAPHICS') == "GL":
+        c_options['use_opengl_es2'] = False
+    elif environ.get('GRAPHICS') == "GLES":
+        c_options['use_opengl_es2'] = True
+    else:
+        print("WARNING: Unknown graphics system choosen - using defaults!")
+
 # now check if environ is changing the default values
 for key in list(c_options.keys()):
     ukey = key.upper()
@@ -177,19 +186,20 @@ elif platform == 'win32':
     print('Windows platform detected, force GLEW usage.')
     c_options['use_glew'] = True
 else:
-    # searching GLES headers
-    default_header_dirs = ['/usr/include', '/usr/local/include']
-    found = False
-    for hdir in default_header_dirs:
-        filename = join(hdir, 'GLES2', 'gl2.h')
-        if exists(filename):
-            found = True
-            print('Found GLES 2.0 headers at {0}'.format(filename))
-            break
-    if not found:
-        print('WARNING: GLES 2.0 headers are not found')
-        print('Fallback to Desktop opengl headers.')
-        c_options['use_opengl_es2'] = False
+    if environ.get('GRAPHICS') is None:
+        # searching GLES headers
+        default_header_dirs = ['/usr/include', '/usr/local/include']
+        found = False
+        for hdir in default_header_dirs:
+            filename = join(hdir, 'GLES2', 'gl2.h')
+            if exists(filename):
+                found = True
+                print('Found GLES 2.0 headers at {0}'.format(filename))
+                break
+        if not found:
+            print('WARNING: GLES 2.0 headers are not found')
+            print('Fallback to Desktop opengl headers.')
+            c_options['use_opengl_es2'] = False
 
 # check if we are in a kivy-ios build
 if platform == 'ios':