Add function to query window content scale

Analogous to glfwGetWindowContentScale().

See comments on libsdl-org#5778

include/SDL_video.h

@@ -1131,6 +1131,36 @@ extern DECLSPEC void SDLCALL SDL_SetWindowMaximumSize(SDL_Window * window,
 extern DECLSPEC void SDLCALL SDL_GetWindowMaximumSize(SDL_Window * window,
                                                       int *w, int *h);
 
+/**
+ * Get the OS-provided scale factor to apply to the contents of the window.
+ * 
+ * The content scale is how much larger the OS wants us to draw elements
+ * like text to match the user's preferences 
+ * (usually based on DPI of the monitor).
+ * 
+ * SDL_GetWindowSizeInPixels() divided by SDL_GetWindowSize() is approximately
+ * equivalent to these values, differing slightly due to rounding behaviors.
+ * 
+ * This value can change if the user changes the scaling settings on the OS, 
+ * or if they have multiple monitors with different scaling settings and drag
+ * the window between them.
+ * The `SDL_WINDOWEVENT_SIZE_CHANGED` window event is raised when this happens.
+ *
+ * \param window the window to query
+ * \param h a pointer filled in with the horizontal content scale of the 
+ *          window, may be NULL
+ * \param v a pointer filled in with the vertical content scale of the
+ *          window, may be NULL
+ *
+ * \since This function is available since SDL 2.25.0.
+ *
+ * \sa SDL_GetWindowSizeInPixels
+ * \sa SDL_GetWindowSize
+ */
+extern DECLSPEC void SDLCALL SDL_GetWindowContentScale(SDL_Window * window, 
+                                                       float * h, float * v);
+
+
 /**
  * Set the border state of a window.
  *

src/dynapi/SDL2.exports

@@ -867,3 +867,4 @@
 ++'_SDL_SensorGetDataWithTimestamp'.'SDL2.dll'.'SDL_SensorGetDataWithTimestamp'
 ++'_SDL_ResetHints'.'SDL2.dll'.'SDL_ResetHints'
 ++'_SDL_strcasestr'.'SDL2.dll'.'SDL_strcasestr'
+++'_SDL_GetWindowContentScale'.'SDL2.dll'.'SDL_GetWindowContentScale'

src/dynapi/SDL_dynapi_overrides.h

@@ -893,3 +893,4 @@
 #define SDL_SensorGetDataWithTimestamp SDL_SensorGetDataWithTimestamp_REAL
 #define SDL_ResetHints SDL_ResetHints_REAL
 #define SDL_strcasestr SDL_strcasestr_REAL
+#define SDL_GetWindowContentScale SDL_GetWindowContentScale_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -976,3 +976,4 @@ SDL_DYNAPI_PROC(int,SDL_GameControllerGetSensorDataWithTimestamp,(SDL_GameContro
 SDL_DYNAPI_PROC(int,SDL_SensorGetDataWithTimestamp,(SDL_Sensor *a, Uint64 *b, float *c, int d),(a,b,c,d),return)
 SDL_DYNAPI_PROC(void,SDL_ResetHints,(void),(),)
 SDL_DYNAPI_PROC(char*,SDL_strcasestr,(const char *a, const char *b),(a,b),return)
+SDL_DYNAPI_PROC(void,SDL_GetWindowContentScale,(SDL_Window *a, float *b, float *c),(a,b,c),)

src/video/SDL_sysvideo.h

@@ -228,6 +228,7 @@ struct SDL_VideoDevice
     void (*SetWindowMaximumSize) (_THIS, SDL_Window * window);
     int (*GetWindowBordersSize) (_THIS, SDL_Window * window, int *top, int *left, int *bottom, int *right);
     void (*GetWindowSizeInPixels)(_THIS, SDL_Window *window, int *w, int *h);
+    void (*GetWindowContentScale)(_THIS, SDL_Window *window, float *h, float *v);
     int (*SetWindowOpacity) (_THIS, SDL_Window * window, float opacity);
     int (*SetWindowModalFor) (_THIS, SDL_Window * modal_window, SDL_Window * parent_window);
     int (*SetWindowInputFocus) (_THIS, SDL_Window * window);

src/video/SDL_video.c

@@ -2494,6 +2494,27 @@ SDL_GetWindowMaximumSize(SDL_Window * window, int *max_w, int *max_h)
     }
 }
 
+void
+SDL_GetWindowContentScale(SDL_Window *window, float *h, float *v)
+{
+    CHECK_WINDOW_MAGIC(window,);
+
+    if (_this->GetWindowContentScale) {
+        _this->GetWindowContentScale(_this, window, h, v);
+    } else {
+        int width, height, pixWidth, pixHeight;
+
+        SDL_GetWindowSize(window, &width, &height);
+        SDL_GetWindowSizeInPixels(window, &pixWidth, &pixHeight);
+
+        if (h)
+            *h = pixWidth / (float) width;
+
+        if (v)
+            *v = pixHeight / (float) height;
+    }
+}
+
 void
 SDL_ShowWindow(SDL_Window * window)
 {

src/video/windows/SDL_windowsvideo.c

@@ -210,6 +210,7 @@ WIN_CreateDevice(void)
     device->SetWindowHitTest = WIN_SetWindowHitTest;
     device->AcceptDragAndDrop = WIN_AcceptDragAndDrop;
     device->FlashWindow = WIN_FlashWindow;
+    device->GetWindowContentScale = WIN_GetWindowContentScale;
 
     device->shape_driver.CreateShaper = Win32_CreateShaper;
     device->shape_driver.SetWindowShape = Win32_SetWindowShape;

src/video/windows/SDL_windowswindow.c

@@ -1504,6 +1504,19 @@ WIN_FlashWindow(_THIS, SDL_Window * window, SDL_FlashOperation operation)
 }
 #endif /*!defined(__XBOXONE__) && !defined(__XBOXSERIES__)*/
 
+void
+WIN_GetWindowContentScale(_THIS, SDL_Window *window, float *h, float *v)
+{
+    const SDL_WindowData *data = ((SDL_WindowData *) window->driverdata);
+
+    float scale = data->scaling_dpi / 96.0f;
+
+    if (h)
+        *h = scale;
+    if (v)
+        *v = scale;
+}
+
 #endif /* SDL_VIDEO_DRIVER_WINDOWS */
 
 /* vi: set ts=4 sw=4 expandtab: */

src/video/windows/SDL_windowswindow.h

@@ -110,6 +110,7 @@ extern void WIN_ClientPointToSDL(const SDL_Window *window, int *w, int *h);
 extern void WIN_ClientPointFromSDL(const SDL_Window *window, int *w, int *h);
 extern void WIN_AcceptDragAndDrop(SDL_Window * window, SDL_bool accept);
 extern int WIN_FlashWindow(_THIS, SDL_Window * window, SDL_FlashOperation operation);
+extern void WIN_GetWindowContentScale(_THIS, SDL_Window *window, float *h, float *v);
 
 /* Ends C function definitions when using C++ */
 #ifdef __cplusplus