Backends: Win32: Added ImGui_ImplWin32_EnableDpiAwareness(), ImGui_ImplWin32_GetDpiScaleForHwnd(), ImGui_ImplWin32_GetDpiScaleForMonitor() helpers functions.

(backported from the docking branch)

docs/CHANGELOG.txt

@@ -42,6 +42,10 @@ Other Changes:
   glyph. (#2149, #515)
 - Font: Fixed non-ASCII space occasionally creating unnecessary empty polygons.
 - Demo: Added a black and white gradient to Demo>Examples>Custom Rendering.
+- Backends: Win32: Added ImGui_ImplWin32_EnableDpiAwareness(), ImGui_ImplWin32_GetDpiScaleForHwnd(),
+  ImGui_ImplWin32_GetDpiScaleForMonitor() helpers functions (backported from the docking branch).
+  Those functions makes it easier for example apps to support hi-dpi features without setting up
+  a manifest.
 - Backends: SDL: Added ImGui_ImplSDL2_InitForMetal() for API consistency (even though the function
   currently does nothing).
 - Examples: Added SDL2+Metal example application. (#3017) [@coding-jackalope]

examples/imgui_impl_win32.cpp

@@ -28,6 +28,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2020-02-17: Added ImGui_ImplWin32_EnableDpiAwareness(), ImGui_ImplWin32_GetDpiScaleForHwnd(), ImGui_ImplWin32_GetDpiScaleForMonitor() helper functions.
 //  2020-01-14: Inputs: Added support for #define IMGUI_IMPL_WIN32_DISABLE_GAMEPAD/IMGUI_IMPL_WIN32_DISABLE_LINKING_XINPUT.
 //  2019-12-05: Inputs: Added support for ImGuiMouseCursor_NotAllowed mouse cursor.
 //  2019-05-11: Inputs: Don't filter value from WM_CHAR before calling AddInputCharacter().
@@ -337,3 +338,102 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
     return 0;
 }
 
+
+//--------------------------------------------------------------------------------------------------------
+// DPI-related helpers (optional)
+//--------------------------------------------------------------------------------------------------------
+// - Use to enable DPI awareness without having to create an application manifest.
+// - Your own app may already do this via a manifest or explicit calls. This is mostly useful for our examples/ apps.
+// - In theory we could call simple functions from Windows SDK such as SetProcessDPIAware(), SetProcessDpiAwareness(), etc.
+//   but most of the functions provided by Microsoft require Windows 8.1/10+ SDK at compile time and Windows 8/10+ at runtime,
+//   neither we want to require the user to have. So we dynamically select and load those functions to avoid dependencies.
+//---------------------------------------------------------------------------------------------------------
+// This is the scheme successfully used by GLFW (from which we borrowed some of the code) and other apps aiming to be highly portable.
+// ImGui_ImplWin32_EnableDpiAwareness() is just a helper called by main.cpp, we don't call it automatically.
+// If you are trying to implement your own back-end for your own engine, you may ignore that noise.
+//---------------------------------------------------------------------------------------------------------
+
+// Implement some of the functions and types normally declared in recent Windows SDK.
+#if !defined(_versionhelpers_H_INCLUDED_) && !defined(_INC_VERSIONHELPERS)
+static BOOL IsWindowsVersionOrGreater(WORD major, WORD minor, WORD sp)
+{
+    OSVERSIONINFOEXW osvi = { sizeof(osvi), major, minor, 0, 0, { 0 }, sp };
+    DWORD mask = VER_MAJORVERSION | VER_MINORVERSION | VER_SERVICEPACKMAJOR;
+    ULONGLONG cond = ::VerSetConditionMask(0, VER_MAJORVERSION, VER_GREATER_EQUAL);
+    cond = ::VerSetConditionMask(cond, VER_MINORVERSION, VER_GREATER_EQUAL);
+    cond = ::VerSetConditionMask(cond, VER_SERVICEPACKMAJOR, VER_GREATER_EQUAL);
+    return ::VerifyVersionInfoW(&osvi, mask, cond);
+}
+#define IsWindows8Point1OrGreater()  IsWindowsVersionOrGreater(HIBYTE(0x0602), LOBYTE(0x0602), 0) // _WIN32_WINNT_WINBLUE
+#endif
+
+#ifndef DPI_ENUMS_DECLARED
+typedef enum { PROCESS_DPI_UNAWARE = 0, PROCESS_SYSTEM_DPI_AWARE = 1, PROCESS_PER_MONITOR_DPI_AWARE = 2 } PROCESS_DPI_AWARENESS;
+typedef enum { MDT_EFFECTIVE_DPI = 0, MDT_ANGULAR_DPI = 1, MDT_RAW_DPI = 2, MDT_DEFAULT = MDT_EFFECTIVE_DPI } MONITOR_DPI_TYPE;
+#endif
+#ifndef _DPI_AWARENESS_CONTEXTS_
+DECLARE_HANDLE(DPI_AWARENESS_CONTEXT);
+#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE    (DPI_AWARENESS_CONTEXT)-3
+#endif
+#ifndef DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2
+#define DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2 (DPI_AWARENESS_CONTEXT)-4
+#endif
+typedef HRESULT(WINAPI* PFN_SetProcessDpiAwareness)(PROCESS_DPI_AWARENESS);                     // Shcore.lib + dll, Windows 8.1+
+typedef HRESULT(WINAPI* PFN_GetDpiForMonitor)(HMONITOR, MONITOR_DPI_TYPE, UINT*, UINT*);        // Shcore.lib + dll, Windows 8.1+
+typedef DPI_AWARENESS_CONTEXT(WINAPI* PFN_SetThreadDpiAwarenessContext)(DPI_AWARENESS_CONTEXT); // User32.lib + dll, Windows 10 v1607+ (Creators Update)
+
+// Helper function to enable DPI awareness without setting up a manifest
+void ImGui_ImplWin32_EnableDpiAwareness()
+{
+    // if (IsWindows10OrGreater()) // This needs a manifest to succeed. Instead we try to grab the function pointer!
+    {
+        static HINSTANCE user32_dll = ::LoadLibraryA("user32.dll"); // Reference counted per-process
+        if (PFN_SetThreadDpiAwarenessContext SetThreadDpiAwarenessContextFn = (PFN_SetThreadDpiAwarenessContext)::GetProcAddress(user32_dll, "SetThreadDpiAwarenessContext"))
+        {
+            SetThreadDpiAwarenessContextFn(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+            return;
+        }
+    }
+    if (IsWindows8Point1OrGreater())
+    {
+        static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process
+        if (PFN_SetProcessDpiAwareness SetProcessDpiAwarenessFn = (PFN_SetProcessDpiAwareness)::GetProcAddress(shcore_dll, "SetProcessDpiAwareness"))
+        {
+            SetProcessDpiAwarenessFn(PROCESS_PER_MONITOR_DPI_AWARE);
+            return;
+        }
+    }
+    SetProcessDPIAware();
+}
+
+#ifdef _MSC_VER
+#pragma comment(lib, "gdi32")   // Link with gdi32.lib for GetDeviceCaps()
+#endif
+
+float ImGui_ImplWin32_GetDpiScaleForMonitor(void* monitor)
+{
+    UINT xdpi = 96, ydpi = 96;
+    if (IsWindows8Point1OrGreater())
+    {
+        static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process
+        if (PFN_GetDpiForMonitor GetDpiForMonitorFn = (PFN_GetDpiForMonitor)::GetProcAddress(shcore_dll, "GetDpiForMonitor"))
+            GetDpiForMonitorFn((HMONITOR)monitor, MDT_EFFECTIVE_DPI, &xdpi, &ydpi);
+    }
+    else
+    {
+        const HDC dc = ::GetDC(NULL);
+        xdpi = ::GetDeviceCaps(dc, LOGPIXELSX);
+        ydpi = ::GetDeviceCaps(dc, LOGPIXELSY);
+        ::ReleaseDC(NULL, dc);
+    }
+    IM_ASSERT(xdpi == ydpi); // Please contact me if you hit this assert!
+    return xdpi / 96.0f;
+}
+
+float ImGui_ImplWin32_GetDpiScaleForHwnd(void* hwnd)
+{
+    HMONITOR monitor = ::MonitorFromWindow((HWND)hwnd, MONITOR_DEFAULTTONEAREST);
+    return ImGui_ImplWin32_GetDpiScaleForMonitor(monitor);
+}
+
+//---------------------------------------------------------------------------------------------------------

examples/imgui_impl_win32.h

@@ -23,3 +23,13 @@ IMGUI_IMPL_API void     ImGui_ImplWin32_NewFrame();
 #if 0
 extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
 #endif
+
+// DPI-related helpers (optional)
+// - Use to enable DPI awareness without having to create an application manifest.
+// - Your own app may already do this via a manifest or explicit calls. This is mostly useful for our examples/ apps.
+// - In theory we could call simple functions from Windows SDK such as SetProcessDPIAware(), SetProcessDpiAwareness(), etc.
+//   but most of the functions provided by Microsoft require Windows 8.1/10+ SDK at compile time and Windows 8/10+ at runtime,
+//   neither we want to require the user to have. So we dynamically select and load those functions to avoid dependencies.
+IMGUI_IMPL_API void     ImGui_ImplWin32_EnableDpiAwareness();
+IMGUI_IMPL_API float    ImGui_ImplWin32_GetDpiScaleForHwnd(void* hwnd);       // HWND hwnd
+IMGUI_IMPL_API float    ImGui_ImplWin32_GetDpiScaleForMonitor(void* monitor); // HMONITOR monitor