Makes Windows DPI aware of scale changes (#8058)

* make dpi aware of scale changes

* Resize on startup if there is any dpi change

* remove workarounds and use SDL_HINT_WINDOWS_DPI_SCALING

kivy/core/window/__init__.py

@@ -420,7 +420,7 @@ class WindowBase(EventDispatcher):
     def _get_size(self):
         r = self._rotation
         w, h = self._size
-        if self._density != 1:
+        if platform == 'win' or self._density != 1:
             w, h = self._win._get_gl_size()
         if self.softinput_mode == 'resize':
             h -= self.keyboard_height
@@ -519,7 +519,7 @@ class WindowBase(EventDispatcher):
     # make some property read-only
     def _get_width(self):
         _size = self._size
-        if self._density != 1:
+        if platform == 'win' or self._density != 1:
             _size = self._win._get_gl_size()
         r = self._rotation
         if r == 0 or r == 180:
@@ -536,7 +536,7 @@ class WindowBase(EventDispatcher):
         '''Rotated window height'''
         r = self._rotation
         _size = self._size
-        if self._density != 1:
+        if platform == 'win' or self._density != 1:
             _size = self._win._get_gl_size()
         kb = self.keyboard_height if self.softinput_mode == 'resize' else 0
         if r == 0 or r == 180:
@@ -739,13 +739,13 @@ class WindowBase(EventDispatcher):
     '''
 
     def _get_effective_size(self):
-        '''On density=1 and non-ios displays, return :attr:`system_size`,
-        else return scaled / rotated :attr:`size`.
+        '''On density=1 and non-ios / non-Windows displays,
+        return :attr:`system_size`, else return scaled / rotated :attr:`size`.
 
         Used by MouseMotionEvent.update_graphics() and WindowBase.on_motion().
         '''
         w, h = self.system_size
-        if platform == 'ios' or self._density != 1:
+        if platform in ('ios', 'win') or self._density != 1:
             w, h = self.size
 
         return w, h

kivy/core/window/_window_sdl2.pyx

@@ -109,6 +109,10 @@ cdef class _WindowSDL2Storage:
 
         SDL_SetHintWithPriority(b'SDL_ANDROID_TRAP_BACK_BUTTON', b'1',
                                 SDL_HINT_OVERRIDE)
+        
+        # makes dpi aware of scale changes
+        if platform == "win":
+            SDL_SetHint(SDL_HINT_WINDOWS_DPI_SCALING, b"1")
 
         if SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK) < 0:
             self.die()

kivy/core/window/window_sdl2.py

@@ -981,8 +981,6 @@ class _WindowsSysDPIWatch:
         from ctypes import windll
 
         if msg == WM_DPICHANGED:
-            ow, oh = self.window.size
-            old_dpi = self.window.dpi
 
             def clock_callback(*args):
                 if x_dpi != y_dpi:
@@ -991,10 +989,6 @@ class _WindowsSysDPIWatch:
 
                 self.window.dpi = x_dpi
 
-                # maintain the same window size
-                ratio = x_dpi / old_dpi
-                self.window.size = ratio * ow, ratio * oh
-
             x_dpi = wParam & 0xFFFF
             y_dpi = wParam >> 16
             Clock.schedule_once(clock_callback, -1)

kivy/lib/sdl2.pxi

@@ -480,6 +480,8 @@ cdef extern from "SDL.h":
     cdef char *SDL_HINT_VIDEO_WIN_D3DCOMPILER
     cdef char *SDL_HINT_ACCELEROMETER_AS_JOYSTICK
     cdef char *SDL_HINT_ANDROID_TRAP_BACK_BUTTON
+    cdef char *SDL_HINT_WINDOWS_DPI_AWARENESS
+    cdef char *SDL_HINT_WINDOWS_DPI_SCALING
 
     cdef int SDL_QUERY               = -1
     cdef int SDL_IGNORE              =  0