Platform: query DPI awareness on Apple and warn if not set.

I'm not really sure if the extra work and link dependencies are worth
the warning, but since I *need* to do something similar for Windows, why
not have it here as well.

modules/FindMagnum.cmake

@@ -639,8 +639,14 @@ foreach(_component ${Magnum_FIND_COMPONENTS})
                 find_package(SDL2)
                 set_property(TARGET Magnum::${_component} APPEND PROPERTY
                     INTERFACE_LINK_LIBRARIES SDL2::SDL2)
-                if(CORRADE_TARGET_UNIX AND NOT CORRADE_TARGET_APPLE)
+                # Use the Foundation framework on Apple to query the DPI awareness
+                if(CORRADE_TARGET_APPLE)
+                    find_library(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY Foundation)
+                    mark_as_advanced(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY)
+                    set_property(TARGET Magnum::${_component} APPEND PROPERTY
+                        INTERFACE_LINK_LIBRARIES ${_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY})
                 # Needed for opt-in DPI queries
+                elseif(CORRADE_TARGET_UNIX)
                     set_property(TARGET Magnum::${_component} APPEND PROPERTY
                         INTERFACE_LINK_LIBRARIES ${CMAKE_DL_LIBS})
                 endif()

src/Magnum/Platform/CMakeLists.txt

@@ -205,6 +205,9 @@ if(WITH_SDL2APPLICATION)
     if(TARGET_GL)
         list(APPEND MagnumSdl2Application_SRCS ${MagnumSomeContext_OBJECTS})
     endif()
+    if(CORRADE_TARGET_APPLE)
+        list(APPEND MagnumSdl2Application_SRCS Implementation/dpiScaling.mm)
+    endif()
 
     add_library(MagnumSdl2Application STATIC
         ${MagnumSdl2Application_SRCS}
@@ -222,8 +225,17 @@ if(WITH_SDL2APPLICATION)
             ${MagnumSomeContext_LIBRARY})
     endif()
 
+    # Use the Foundation framework on Apple to query the DPI awareness
+    if(CORRADE_TARGET_APPLE)
+        find_library(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY Foundation)
+        mark_as_advanced(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY)
+        find_path(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_INCLUDE_DIR NAMES NSBundle.h)
+        mark_as_advanced(_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_INCLUDE_DIR)
+        target_link_libraries(MagnumSdl2Application PUBLIC ${_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_LIBRARY})
+        target_include_directories(MagnumSdl2Application PRIVATE ${_MAGNUM_APPLE_FOUNDATION_FRAMEWORK_INCLUDE_DIR})
+
     # If there is X11, ask it for DPI
-    if(CORRADE_TARGET_UNIX AND NOT CORRADE_TARGET_APPLE)
+    elseif(CORRADE_TARGET_UNIX)
         find_package(X11)
         if(X11_FOUND)
             # Not linking to X11, we dlopen() instead

src/Magnum/Platform/Implementation/dpiScaling.hpp

@@ -40,7 +40,9 @@
 #include <emscripten/html5.h>
 #endif
 
-namespace Magnum { namespace Platform { namespace Implementation { namespace {
+namespace Magnum { namespace Platform { namespace Implementation {
+
+namespace {
 
 inline Utility::Arguments windowScalingArguments() {
     Utility::Arguments args{"magnum"};
@@ -126,6 +128,12 @@ inline Float emscriptenDpiScaling() {
 }
 #endif
 
-}}}}
+}
+
+#ifdef CORRADE_TARGET_APPLE
+bool isAppleBundleHiDpiEnabled();
+#endif
+
+}}}
 
 #endif

src/Magnum/Platform/Implementation/dpiScaling.mm

@@ -0,0 +1,40 @@
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018
+              Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#import "NSBundle.h"
+
+#include "dpiScaling.hpp"
+
+namespace Magnum { namespace Platform { namespace Implementation {
+
+/* HiDPI is available only for bundles, so if the executable is not a bundle,
+   return false */
+bool isAppleBundleHiDpiEnabled() {
+    NSBundle* bundle = [NSBundle mainBundle];
+    if(!bundle) return false;
+    return bool([bundle objectForInfoDictionaryKey:@"NSHighResolutionCapable"]);
+}
+
+}}}

src/Magnum/Platform/Sdl2Application.cpp

@@ -135,6 +135,15 @@ void Sdl2Application::create(const Configuration& configuration, const GLConfigu
 Vector2 Sdl2Application::dpiScaling(const Configuration& configuration) const {
     std::ostream* verbose = _verboseLog ? Debug::output() : nullptr;
 
+    /* Print a helpful warning in case some extra steps are needed for HiDPI
+       support */
+    #ifdef CORRADE_TARGET_APPLE
+    if(!Implementation::isAppleBundleHiDpiEnabled())
+        Warning{} << "Platform::Sdl2Application: warning: the executable is not a HiDPI-enabled app bundle";
+    #elif defined(CORRADE_TARGET_WINDOWS)
+    /** @todo */
+    #endif
+
     /* Use values from the configuration only if not overriden on command line.
        In any case explicit scaling has a precedence before the policy. */
     Implementation::DpiScalingPolicy dpiScalingPolicy{};

src/Magnum/Platform/Test/CMakeLists.txt

@@ -58,8 +58,10 @@ if(WITH_SDL2APPLICATION)
             ../WebApplication.css
             Sdl2ApplicationTest.html
             DESTINATION ${CMAKE_CURRENT_BINARY_DIR})
-    elseif(CORRADE_TARGET_IOS)
+    elseif(CORRADE_TARGET_IOS OR CORRADE_TARGET_APPLE)
+        # The plist is needed in order to mark the app as DPI-aware
         set_target_properties(PlatformSdl2ApplicationTest PROPERTIES
+            MACOSX_BUNDLE_INFO_PLIST ${CMAKE_CURRENT_SOURCE_DIR}/Sdl2ApplicationTest.plist
             MACOSX_BUNDLE ON
             XCODE_ATTRIBUTE_CODE_SIGNING_REQUIRED "YES")
     endif()

src/Magnum/Platform/Test/Sdl2ApplicationTest.plist

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+  <key>CFBundleDevelopmentRegion</key>
+  <string>en-US</string>
+  <key>CFBundleExecutable</key>
+  <string>${MACOSX_BUNDLE_EXECUTABLE_NAME}</string>
+  <key>CFBundleIdentifier</key>
+  <string>cz.mosra.magnum.Sdl2ApplicationTest</string>
+  <key>CFBundleInfoDictionaryVersion</key>
+  <string>6.0</string>
+  <key>CFBundleName</key>
+  <string>Magnum Triangle</string>
+  <key>CFBundlePackageType</key>
+  <string>APPL</string>
+  <key>NSHighResolutionCapable</key>
+  <true/>
+</dict>
+</plist>