Backends: GLFW, SDL2, SDL3, update for docking to use helpers.

backends/imgui_impl_glfw.cpp

@@ -962,14 +962,10 @@ static void ImGui_ImplGlfw_UpdateMonitors()
             monitor.WorkSize = ImVec2((float)w, (float)h);
         }
 #endif
-#if GLFW_HAS_PER_MONITOR_DPI
-        // Warning: the validity of monitor DPI information on Windows depends on the application DPI awareness settings, which generally needs to be set in the manifest or at runtime.
-        float x_scale, y_scale;
-        glfwGetMonitorContentScale(glfw_monitors[n], &x_scale, &y_scale);
-        if (x_scale == 0.0f)
+        float scale = ImGui_ImplGlfw_GetContentScaleForMonitor(glfw_monitors[n]);
+        if (scale == 0.0f)
             continue; // Some accessibility applications are declaring virtual monitors with a DPI of 0, see #7902.
-        monitor.DpiScale = x_scale;
-#endif
+        monitor.DpiScale = scale;
         monitor.PlatformHandle = (void*)glfw_monitors[n]; // [...] GLFW doc states: "guaranteed to be valid only until the monitor configuration changes"
         platform_io.Monitors.push_back(monitor);
     }

backends/imgui_impl_sdl2.cpp

@@ -956,17 +956,10 @@ static void ImGui_ImplSDL2_UpdateMonitors()
             monitor.WorkSize = ImVec2((float)r.w, (float)r.h);
         }
 #endif
-#if SDL_HAS_PER_MONITOR_DPI
-        // FIXME-VIEWPORT: On MacOS SDL reports actual monitor DPI scale, ignoring OS configuration. We may want to set
-        //  DpiScale to cocoa_window.backingScaleFactor here.
-        float dpi = 0.0f;
-        if (!SDL_GetDisplayDPI(n, &dpi, nullptr, nullptr))
-        {
-            if (dpi <= 0.0f)
-                continue; // Some accessibility applications are declaring virtual monitors with a DPI of 0, see #7902.
-            monitor.DpiScale = dpi / 96.0f;
-        }
-#endif
+        float dpi_scale = ImGui_ImplSDL2_GetContentScaleForDisplay(n);
+        if (dpi_scale <= 0.0f)
+            continue; // Some accessibility applications are declaring virtual monitors with a DPI of 0, see #7902.
+        monitor.DpiScale = dpi_scale;
         monitor.PlatformHandle = (void*)(intptr_t)n;
         platform_io.Monitors.push_back(monitor);
     }

backends/imgui_impl_sdl3.cpp

@@ -897,9 +897,7 @@ static void ImGui_ImplSDL3_UpdateMonitors()
             monitor.WorkPos = ImVec2((float)r.x, (float)r.y);
             monitor.WorkSize = ImVec2((float)r.w, (float)r.h);
         }
-        // FIXME-VIEWPORT: On MacOS SDL reports actual monitor DPI scale, ignoring OS configuration. We may want to set
-        //  DpiScale to cocoa_window.backingScaleFactor here.
-        monitor.DpiScale = SDL_GetDisplayContentScale(display_id);
+        monitor.DpiScale = SDL_GetDisplayContentScale(display_id); // See https://wiki.libsdl.org/SDL3/README-highdpi for details.
         monitor.PlatformHandle = (void*)(intptr_t)n;
         if (monitor.DpiScale <= 0.0f)
             continue; // Some accessibility applications are declaring virtual monitors with a DPI of 0, see #7902.