Platform: HiDPI support for SDL2 and GLFW on Windows.

Co-authored-by: Guillaume Jacquemin <williamjcm@users.noreply.github.com>

doc/changelog.dox

@@ -79,6 +79,10 @@ See also:
 
 @subsubsection changelog-latest-new-platform Platform libraries
 
+-   @ref Platform::Sdl2Application and @ref Platform::GlfwApplication are now
+    DPI-aware on Windows as well. See their documentation,
+    @ref platforms-windows-hidpi and [mosra/magnum#243](https://github.com/mosra/magnum/issues/243)
+    for more information.
 -   Added @ref Platform::Sdl2Application::glContext() to access the underlying
     `SDL_GLContext` (see [mosra/magnum#325](https://github.com/mosra/magnum/pull/325))
 

doc/platforms-windows.dox

@@ -34,9 +34,74 @@ namespace Magnum {
 
 @section platforms-windows-hidpi HiDPI support
 
-Windows supports two approaches to advertising HiDPI support --- either via the
-manifest file or through the [SetProcessDpiAwareness()](https://docs.microsoft.com/en-us/windows/desktop/api/shellscalingapi/nf-shellscalingapi-setprocessdpiawareness)
-API. See the API documentation for more information.
+Windows supports two approaches to advertising HiDPI support. The recommended
+way is via a so-called manifest file added to an executable, but it's also
+possible to it programatically through the `SetProcessDpiAwareness()` family of
+APIs. Note there's three different levels of DPI awareness setup for Windows
+Vista and newer, Windows 8.1 and newer and Windows 10, and for best support may
+want to support all three.
+
+When using MSVC, the manifest file can be added directly via CMake. Advertising application-wide per-monitor support can look like in the following snippet,
+together with fallbacks for older systems:
+
+@code{.xml}
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0"
+          xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
+<asmv3:application>
+  <asmv3:windowsSettings>
+    <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
+      true/pm
+    </dpiAware> <!-- legacy -->
+    <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">
+      permonitorv2,permonitor
+    </dpiAwareness> <!-- falls back to pm if pmv2 is not available -->
+  </asmv3:windowsSettings>
+</asmv3:application>
+</assembly>
+@endcode
+
+Then, the manifest file can be supplied directly in the sources list for
+@cmake add_executable() @ce, via a variable, or you can add it conditionally
+later using @cmake target_sources() @ce. For example:
+
+@code{.cmake}
+add_executable(my-application MyApplication.cpp)
+if(CORRADE_TARGET_WINDOWS)
+    target_sources(my-application PRIVATE WindowsHiDPI.manifest)
+endif()
+@endcode
+
+Some toolkits (such as GLFW in @ref Platform-GlfwApplication-dpi "Platform::GlfwApplication")
+are advertising HiDPI support implicitly programatically. In that case the
+manifest file doesn't need to be supplied, but there may be some disadvantages
+compared to supplying the manifest. See the
+[MSDN documentation about DPI awareness](https://msdn.microsoft.com/en-us/library/windows/desktop/mt846517(v=vs.85).aspx)
+for more information.
+
+@m_class{m-block m-info}
+
+@par Supplying manifests with MinGW
+    With MinGw the operation is slightly more involved, as you need to pass it
+    through a `*.rc` file. A downside is that MinGW is not able to merge
+    information from multiple manifests like the MSVC toolchain can.
+@par
+    @code{.txt}
+    1 RT_MANIFEST "WindowsHiDPI.manifest"
+    @endcode
+@par
+    Then you add the `*.rc` file using @cb{.cmake} target_sources @ce like
+    above. Here's a CMake snippet that will work for both:
+@par
+    @code{.cmake}
+    add_executable(my-application MyApplication.cpp)
+    if(CORRADE_TARGET_WINDOWS)
+        if(MSVC)
+            target_sources(my-application PRIVATE WindowsHiDPI.manifest)
+        elif(MINGW)
+            target_sources(my-application PRIVATE WindowsHiDPI.rc)
+        endif()
+    endif()
+    @endcode
 
 @section platforms-windows-rt Windows RT
 

src/Magnum/Platform/GlfwApplication.cpp

@@ -149,6 +149,7 @@ Vector2 GlfwApplication::dpiScaling(const Configuration& configuration) const {
     /* Otherwise there's a choice between virtual and physical DPI scaling */
     #else
     /* Try to get virtual DPI scaling first, if supported and requested */
+    /** @todo Revisit this for GLFW 3.3 -- https://github.com/glfw/glfw/issues/677 */
     if(dpiScalingPolicy == Implementation::GlfwDpiScalingPolicy::Virtual) {
         /* Use Xft.dpi on X11 */
         #ifdef _MAGNUM_PLATFORM_USE_X11
@@ -158,6 +159,28 @@ Vector2 GlfwApplication::dpiScaling(const Configuration& configuration) const {
             return dpiScaling;
         }
 
+        /* Check for DPI awareness on non-RT Windows and then ask for DPI. GLFW
+           is advertising the application to be DPI-aware on its own even
+           without supplying an explicit manifest --
+           https://github.com/glfw/glfw/blob/089ea9af227fdffdf872348923e1c12682e63029/src/win32_init.c#L564-L569
+           If, for some reason, the app is still not DPI-aware, tell that to
+           the user explicitly and don't even attempt to query the value if the
+           app is not DPI aware. If it's desired to get the DPI value
+           unconditionally, the user should use physical DPI scaling instead. */
+        #elif defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
+        if(!Implementation::isWindowsAppDpiAware()) {
+            Warning{verbose} << "Platform::GlfwApplication: your application is not set as DPI-aware, DPI scaling won't be used";
+            return Vector2{1.0f};
+        }
+        GLFWmonitor* const monitor = glfwGetPrimaryMonitor();
+        const GLFWvidmode* const mode = glfwGetVideoMode(monitor);
+        Vector2i monitorSize;
+        glfwGetMonitorPhysicalSize(monitor, &monitorSize.x(), &monitorSize.y());
+        auto dpi = Vector2{Vector2i{mode->width, mode->height}*25.4f/Vector2{monitorSize}};
+        const Vector2 dpiScaling{dpi/96.0f};
+        Debug{verbose} << "Platform::GlfwApplication: virtual DPI scaling" << dpiScaling;
+        return dpiScaling;
+
         /* Otherwise ¯\_(ツ)_/¯ */
         #else
         Debug{verbose} << "Platform::GlfwApplication: sorry, virtual DPI scaling not implemented on this platform yet, falling back to physical DPI scaling";
@@ -168,9 +191,11 @@ Vector2 GlfwApplication::dpiScaling(const Configuration& configuration) const {
        scaling is requested */
     CORRADE_INTERNAL_ASSERT(dpiScalingPolicy == Implementation::GlfwDpiScalingPolicy::Virtual || dpiScalingPolicy == Implementation::GlfwDpiScalingPolicy::Physical);
 
-    /* Take display DPI. Enable only on Linux for now, I need to test this
-       properly on Windows first. */
-    #ifdef CORRADE_TARGET_UNIX
+    /* Take display DPI elsewhere. Enable only on Linux (where it gets the
+       usually very-off value from X11) and on non-RT Windows (where it takes
+       the UI scale value like with virtual DPI scaling, but without checking
+       for DPI awareness first). */
+    #if defined(CORRADE_TARGET_UNIX) || (defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT))
     GLFWmonitor* const monitor = glfwGetPrimaryMonitor();
     const GLFWvidmode* const mode = glfwGetVideoMode(monitor);
     Vector2i monitorSize;

src/Magnum/Platform/GlfwApplication.h

@@ -130,9 +130,11 @@ If no other application header is included, this class is also aliased to
 @section Platform-GlfwApplication-dpi DPI awareness
 
 DPI awareness behavior is consistent with @ref Sdl2Application except that iOS
-or Emscripten specifics don't apply here. See
-@ref Platform-Sdl2Application-dpi "its DPI awareness documentation" for more
-information.
+or Emscripten specifics don't apply here. In addition, on Windows, GLFW is
+implicitly advertising DPI awareness, so the manifest file described in
+@ref platforms-windows-hidpi doesn't necessarily need to be supplied. See
+@ref Platform-Sdl2Application-dpi "Sdl2Application DPI awareness documentation"
+for more information.
 */
 class GlfwApplication {
     public:

src/Magnum/Platform/Implementation/DpiScaling.cpp

@@ -45,6 +45,18 @@
 #include <emscripten/emscripten.h>
 #endif
 
+#if defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
+#define WIN32_LEAN_AND_MEAN 1
+#define VC_EXTRALEAN
+#include <windows.h>
+#ifdef __has_include
+#if __has_include(<shellscalingapi.h>)
+#include <shellscalingapi.h>
+#endif
+#endif
+#include <Corrade/Utility/Assert.h>
+#endif
+
 namespace Magnum { namespace Platform { namespace Implementation {
 
 Utility::Arguments windowScalingArguments() {
@@ -129,6 +141,37 @@ Float emscriptenDpiScaling() {
 }
 #endif
 
+#if defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
+bool isWindowsAppDpiAware() {
+    /** @todo use GetWindowDpiAwarenessContext() (since Windows 10)? I think
+        it's not needed for a simple boolean return value. */
+
+    #ifdef DPI_ENUMS_DECLARED
+    /* The GetProcessDpiAwareness() function is available only since Windows
+       8.1, so load it manually to avoid a link-time error when building for
+       Windows 7. Also, the shellscalingapi.h include might not be available
+       on older MinGW, so it's guarded by __has_include(). Here, if the
+       DPI_ENUMS_DECLARED define is present, the header exists and has what we
+       need. */
+    HMODULE const shcore = GetModuleHandleA("Shcore.dll");
+    if(shcore) {
+        auto* const getProcessDpiAwareness = reinterpret_cast<HRESULT(*)(HANDLE, PROCESS_DPI_AWARENESS*)>(GetProcAddress(shcore, "GetProcessDpiAwareness"));
+        PROCESS_DPI_AWARENESS result{};
+        return getProcessDpiAwareness && getProcessDpiAwareness(nullptr, &result) == S_OK && result != PROCESS_DPI_UNAWARE;
+    }
+    #endif
+
+    /* IsProcessDPIAware() is available since Windows Vista. At this point we
+       can require it (XP support? haha no), so assert that everything works
+       correctly. */
+    HMODULE const user32 = GetModuleHandleA("User32.dll");
+    CORRADE_INTERNAL_ASSERT(user32);
+    auto const isProcessDPIAware = reinterpret_cast<BOOL(*)()>(GetProcAddress(user32, "IsProcessDPIAware"));
+    CORRADE_INTERNAL_ASSERT(isProcessDPIAware);
+    return isProcessDPIAware();
+}
+#endif
+
 }}}
 
 #endif

src/Magnum/Platform/Implementation/DpiScaling.h

@@ -48,6 +48,10 @@ Float emscriptenDpiScaling();
 bool isAppleBundleHiDpiEnabled();
 #endif
 
+#if defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
+bool isWindowsAppDpiAware();
+#endif
+
 }}}
 
 #endif

src/Magnum/Platform/Sdl2Application.cpp

@@ -199,6 +199,26 @@ Vector2 Sdl2Application::dpiScaling(const Configuration& configuration) const {
             return dpiScaling;
         }
 
+        /* Check for DPI awareness on (non-RT) Windows and then ask for DPI.
+           SDL_GetDisplayDPI() is querying GetDpiForMonitor() --
+           https://github.com/spurious/SDL-mirror/blob/17af4584cb28cdb3c2feba17e7d989a806007d9f/src/video/windows/SDL_windowsmodes.c#L266
+           and GetDpiForMonitor() returns 96 if the application is DPI unaware.
+           So we instead check for DPI awareness first (and tell the user if
+           not), and only if the app is, then we use SDL_GetDisplayDPI(). If
+           it's for some reason desired to get the DPI value unconditionally,
+           the user should use physical DPI scaling instead. */
+        #elif defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT)
+        if(!Implementation::isWindowsAppDpiAware()) {
+            Warning{verbose} << "Platform::Sdl2Application: your application is not set as DPI-aware, DPI scaling won't be used";
+            return Vector2{1.0f};
+        }
+        Vector2 dpi;
+        if(SDL_GetDisplayDPI(0, nullptr, &dpi.x(), &dpi.y()) == 0) {
+            const Vector2 dpiScaling{dpi/96.0f};
+            Debug{verbose} << "Platform::Sdl2Application: virtual DPI scaling" << dpiScaling;
+            return dpiScaling;
+        }
+
         /* Otherwise ¯\_(ツ)_/¯ */
         #else
         Debug{verbose} << "Platform::Sdl2Application: sorry, virtual DPI scaling not implemented on this platform yet, falling back to physical DPI scaling";
@@ -220,9 +240,11 @@ Vector2 Sdl2Application::dpiScaling(const Configuration& configuration) const {
     Debug{verbose} << "Platform::Sdl2Application: physical DPI scaling" << dpiScaling.x();
     return dpiScaling;
 
-    /* Take display DPI elsewhere. Enable only on Linux for now, I need to
-       test this properly on Windows first. Also only since SDL 2.0.4. */
-    #elif defined(CORRADE_TARGET_UNIX) && SDL_VERSION_ATLEAST(2, 0, 4)
+    /* Take display DPI elsewhere. Enable only on Linux (where it gets the
+       usually very-off value from X11) and on non-RT Windows (where it takes
+       the UI scale value like with virtual DPI scaling, but without checking
+       for DPI awareness first). Also only since SDL 2.0.4. */
+    #elif (defined(CORRADE_TARGET_UNIX) || (defined(CORRADE_TARGET_WINDOWS) && !defined(CORRADE_TARGET_WINDOWS_RT))) && SDL_VERSION_ATLEAST(2, 0, 4)
     Vector2 dpi;
     if(SDL_GetDisplayDPI(0, nullptr, &dpi.x(), &dpi.y()) == 0) {
         const Vector2 dpiScaling{dpi/96.0f};

src/Magnum/Platform/Sdl2Application.h

@@ -339,8 +339,11 @@ variable).
     system. For example if a 800x600 window is requested and DPI scaling is set
     to 200%, the resulting window will have 1600x1200 pixels. The backing
     framebuffer will have the same size. This is supported on Linux and
-    Windows. Equivalent to passing @ref Configuration::DpiScalingPolicy::Virtual
-    to @ref Configuration::setSize() or `virtual` on command line.
+    Windows; on Windows the application is first checked for DPI awareness
+    as described in @ref platforms-windows-hidpi and if the application is not
+    DPI-aware, 1:1 scaling is used. Equivalent to passing
+    @ref Configuration::DpiScalingPolicy::Virtual to
+    @ref Configuration::setSize() or `virtual` on command line.
 -   Physical DPI scaling. Takes the requested window size as a physical size
     that a window would have on platform's default DPI and scales it to have
     the same physical size on given display physical DPI. So, for example on a
@@ -349,9 +352,10 @@ variable).
     DPI display. On platforms that don't have a concept of a window (such
     as mobile platforms or @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten"), it
     causes the framebuffer to match display pixels 1:1 without any scaling.
-    This is supported on Linux, Windows, all mobile platforms except iOS and
-    Emscripten. Equivalent to passing
-    @ref Configuration::DpiScalingPolicy::Physical to
+    This is supported on Linux and all mobile platforms (except iOS) and
+    Emscripten. On Windows this is equivalent to virtual DPI scaling but
+    without doing an explicit check for DPI awareness first. Equivalent to
+    passing @ref Configuration::DpiScalingPolicy::Physical to
     @ref Configuration::setSize() or `physical` via command line / environment.
 
 Besides the above, it's possible to supply a custom DPI scaling value to

src/Magnum/Platform/Test/CMakeLists.txt

@@ -34,6 +34,7 @@ endif()
 
 if(WITH_GLFWAPPLICATION)
     add_executable(PlatformGlfwApplicationTest GlfwApplicationTest.cpp)
+    # HiDPi.manifest not needed, as GLFW sets that on its own
     target_link_libraries(PlatformGlfwApplicationTest PRIVATE MagnumGlfwApplication)
     set_target_properties(PlatformGlfwApplicationTest PROPERTIES FOLDER "Magnum/Platform/Test")
 endif()
@@ -52,6 +53,13 @@ endif()
 
 if(WITH_SDL2APPLICATION)
     add_executable(PlatformSdl2ApplicationTest Sdl2ApplicationTest.cpp)
+    if(CORRADE_TARGET_WINDOWS AND NOT CORRADE_TARGET_WINDOWS_RT)
+        if(MSVC)
+            target_sources(PlatformSdl2ApplicationTest PRIVATE WindowsHiDPI.manifest)
+        elseif(MINGW)
+            target_sources(PlatformSdl2ApplicationTest PRIVATE WindowsHiDPI.rc)
+        endif()
+    endif()
     target_link_libraries(PlatformSdl2ApplicationTest PRIVATE MagnumSdl2Application)
     set_target_properties(PlatformSdl2ApplicationTest PROPERTIES FOLDER "Magnum/Platform/Test")
     if(CORRADE_TARGET_EMSCRIPTEN)

src/Magnum/Platform/Test/WindowsHiDPI.manifest

@@ -0,0 +1,14 @@
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0"
+          xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
+<asmv3:application>
+  <asmv3:windowsSettings>
+    <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
+      true/pm
+    </dpiAware> <!-- legacy -->
+    <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">
+      permonitorv2,permonitor
+    </dpiAwareness> <!-- falls back to pm if pmv2 is not available -->
+  </asmv3:windowsSettings>
+</asmv3:application>
+</assembly>
+<!-- kate: hl xml; -->

src/Magnum/Platform/Test/WindowsHiDPI.rc

@@ -0,0 +1 @@
+1 RT_MANIFEST "WindowsHiDPI.manifest"