Also send DPI change when expected resize.

src/video/windows/SDL_windowsevents.c

@@ -1538,6 +1538,16 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                 /* This DPI change is coming from an explicit SetWindowPos call within SDL.
                    Assume all call sites are calculating the DPI-aware frame correctly, so
                    we don't need to do any further adjustment. */
+
+                if (data->videodata->dpi_scaling_enabled) {
+                    /* Update the cached DPI value for this window */
+                    data->scaling_dpi = newDPI;
+
+                    /* Send a SDL_WINDOWEVENT_SIZE_CHANGED saying that the client size (in dpi-scaled points) is unchanged.
+                       Renderers need to get this to know that the framebuffer size changed. */
+                    SDL_SendWindowEvent(data->window, SDL_WINDOWEVENT_SIZE_CHANGED, data->window->w, data->window->h);
+                }
+
 #ifdef HIGHDPI_DEBUG
                 SDL_Log("WM_DPICHANGED: Doing nothing, assuming window is already sized correctly");
 #endif