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

@@ -102,18 +102,19 @@ inline Float x11DpiScaling() {
     Containers::ScopedExit closeDisplay{display, xCloseDisplay};
 
     const char* rms = xResourceManagerString(display);
-    CORRADE_INTERNAL_ASSERT(rms);
-    XrmDatabase db = xrmGetStringDatabase(rms);
-    CORRADE_INTERNAL_ASSERT(db);
-    Containers::ScopedExit closeDb{db, xrmDestroyDatabase};
-
-    XrmValue value;
-    char* type{};
-    if(xrmGetResource(db, "Xft.dpi", "Xft.Dpi", &type, &value)) {
-        if(type && strcmp(type, "String") == 0) {
-            const float scaling = std::stof(value.addr)/96.0f;
-            CORRADE_INTERNAL_ASSERT(scaling);
-            return scaling;
+    if(rms) {
+        XrmDatabase db = xrmGetStringDatabase(rms);
+        CORRADE_INTERNAL_ASSERT(db);
+        Containers::ScopedExit closeDb{db, xrmDestroyDatabase};
+
+        XrmValue value;
+        char* type{};
+        if(xrmGetResource(db, "Xft.dpi", "Xft.Dpi", &type, &value)) {
+            if(type && strcmp(type, "String") == 0) {
+                const float scaling = std::stof(value.addr)/96.0f;
+                CORRADE_INTERNAL_ASSERT(scaling);
+                return scaling;
+            }
         }
     }