Graphics: Add Sdl2 vsync (#4854)

* Add support for vsync configuration.

* Accept all integers.

* Bump config version.

* The added version is now 2.1.0.

kivy/config.py

@@ -238,6 +238,12 @@ Available configuration tokens
     `allow_screensaver`: int, one of 0 or 1, defaults to 1
         Allow the device to show a screen saver, or to go to sleep
         on mobile devices. Only works for the sdl2 window provider.
+    `vsync`: `none`, empty value, or integers
+        Whether vsync is enabled, currently only used with sdl2 window.
+        Possible values are `none` or empty value -- leaves it unchanged,
+        ``0`` -- disables vsync, ``1`` or larger -- sets vsync interval,
+        ``-1`` sets adaptive vsync. It falls back to 1 if setting to ``2+``
+        or ``-1`` failed. See ``SDL_GL_SetSwapInterval``.
 
 :input:
 
@@ -309,6 +315,9 @@ Available configuration tokens
     Check the specific module's documentation for a list of accepted
     arguments.
 
+.. versionchanged:: 2.1.0
+    `vsync` has been added to the graphics section
+
 .. versionchanged:: 1.10.0
     `min_state_time`  and `allow_screensaver` have been added
     to the `graphics` section.
@@ -360,7 +369,7 @@ from weakref import ref
 _is_rpi = exists('/opt/vc/include/bcm_host.h')
 
 # Version number of current configuration format
-KIVY_CONFIG_VERSION = 21
+KIVY_CONFIG_VERSION = 22
 
 Config = None
 '''The default Kivy configuration object. This is a :class:`ConfigParser`
@@ -750,7 +759,6 @@ if not environ.get('KIVY_DOC_INCLUDE'):
             Config.setdefault('graphics', 'rotation', '0')
             Config.setdefault('graphics', 'show_cursor', '1')
             Config.setdefault('graphics', 'top', '0')
-            Config.setdefault('graphics', 'vsync', '1')
             Config.setdefault('graphics', 'width', '800')
 
             # input configuration
@@ -786,7 +794,6 @@ if not environ.get('KIVY_DOC_INCLUDE'):
             Config.setdefault('widgets', 'list_trigger_distance', '5')
 
         elif version == 1:
-            Config.remove_option('graphics', 'vsync')
             Config.set('graphics', 'maxfps', '60')
 
         elif version == 2:
@@ -880,6 +887,9 @@ if not environ.get('KIVY_DOC_INCLUDE'):
         elif version == 20:
             Config.setdefault('network', 'useragent', 'curl')
 
+        elif version == 21:
+            Config.setdefault('graphics', 'vsync', '')
+
         else:
             # for future.
             break

kivy/core/window/_window_sdl2.pyx

@@ -233,6 +233,22 @@ cdef class _WindowSDL2Storage:
             if not self.ctx:
                 self.die()
 
+        # vsync
+        vsync = Config.get('graphics', 'vsync')
+        if vsync and vsync != 'none':
+            vsync = Config.getint('graphics', 'vsync')
+
+            Logger.debug(f'WindowSDL: setting vsync interval=={vsync}')
+            res = SDL_GL_SetSwapInterval(vsync)
+
+            if res == -1:
+                status = ''
+                if vsync not in (0, 1):
+                    res = SDL_GL_SetSwapInterval(1)
+                    status = ', trying fallback to 1: ' + 'failed' if res == -1 else 'succeeded'
+
+                Logger.debug('WindowSDL: requested vsync failed' + status)
+
         # Open all available joysticks
         cdef int joy_i
         for joy_i in range(SDL_NumJoysticks()):