Add CreationError::NoAvailablePixelFormat

src/api/cocoa/mod.rs

@@ -603,7 +603,7 @@ impl Window {
                     Err(CreationError::NotSupported)
                 }
             } else {
-                Err(CreationError::NotSupported)
+                Err(CreationError::NoAvailablePixelFormat)
             }
         }
     }

src/api/wgl/mod.rs

@@ -573,5 +573,5 @@ fn choose_dummy_pixel_format<I>(iter: I) -> Result<libc::c_int, CreationError>
         }
     }
 
-    backup_id.ok_or(CreationError::NotSupported)
+    backup_id.ok_or(CreationError::OsError("No available pixel format".to_string()))
 }