Platform: don't assert on X11 DEs that don't have RESOURCE_MANAGER.

doc/changelog.dox

@@ -45,6 +45,9 @@ See also:
     as an alternative to `--magnum-dpi-scaling` command-line parameter. It was
     also not documented anywhere. Besides that, the default `--magnum-dpi-scaling`
     value should have been `default` as documented, not `virtual`.
+-   Don't assert in DPI scaling detection in @ref Platform::Sdl2Application and
+    @ref Platform::GlfwApplication on X11 DEs that don't create any
+    `RESOURCE_MANAGER` (see [mosra/magnum#290](https://github.com/mosra/magnum/issues/290))
 
 @section changelog-2018-10 2018.10
 

src/Magnum/Platform/Implementation/dpiScaling.hpp

@@ -102,7 +102,7 @@ inline Float x11DpiScaling() {
     Containers::ScopedExit closeDisplay{display, xCloseDisplay};
 
     const char* rms = xResourceManagerString(display);
-    CORRADE_INTERNAL_ASSERT(rms);
+    if(rms) {
         XrmDatabase db = xrmGetStringDatabase(rms);
         CORRADE_INTERNAL_ASSERT(db);
         Containers::ScopedExit closeDb{db, xrmDestroyDatabase};
@@ -116,6 +116,7 @@ inline Float x11DpiScaling() {
                 return scaling;
             }
         }
+    }
 
     Warning{} << "Platform: can't get Xft.dpi property for virtual DPI scaling, falling back to physical DPI";
     return {};