5 files changed, 90 insertions, 4 deletions

diff --git a/src/mac.m b/src/mac.m
index 67422a5..9cd3e1c 100644
--- a/src/mac.m
+++ b/src/mac.m
@@ -35,10 +35,12 @@ rectToScreen(NSScreen* screen, NSRect rect)
 }
 
 static NSScreen*
-viewScreen(PuglView* view)
+viewScreen(const PuglView* view)
 {
   return view->impl->window ? [view->impl->window screen]
-                            : [NSScreen mainScreen];
+         : [view->impl->wrapperView window]
+           ? [[view->impl->wrapperView window] screen]
+           : [NSScreen mainScreen];
 }
 
 static NSRect
@@ -1365,6 +1367,12 @@ puglSetWindowTitle(PuglView* view, const char* title)
   return PUGL_SUCCESS;
 }
 
+double
+puglGetScaleFactor(const PuglView* const view)
+{
+  return [viewScreen(view) backingScaleFactor];
+}
+
 PuglStatus
 puglSetFrame(PuglView* view, const PuglRect frame)
 {
diff --git a/src/win.c b/src/win.c
index 8f2a26b..5e70b6f 100644
--- a/src/win.c
+++ b/src/win.c
@@ -35,6 +35,8 @@
 #define PUGL_USER_TIMER_MIN 9470
 
 typedef BOOL(WINAPI* PFN_SetProcessDPIAware)(void);
+typedef HRESULT(WINAPI* PFN_GetProcessDpiAwareness)(HANDLE, DWORD*);
+typedef HRESULT(WINAPI* PFN_GetScaleFactorForMonitor)(HMONITOR, DWORD*);
 
 LRESULT CALLBACK
 wndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam);
@@ -112,6 +114,35 @@ puglWinGetWindowExFlags(const PuglView* const view)
   return WS_EX_NOINHERITLAYOUT | (view->parent ? 0u : WS_EX_APPWINDOW);
 }
 
+static double
+puglWinGetViewScaleFactor(const PuglView* const view)
+{
+  const HMODULE shcore = LoadLibrary("Shcore.dll");
+  if (!shcore) {
+    return 1.0;
+  }
+
+  const PFN_GetProcessDpiAwareness GetProcessDpiAwareness =
+    (PFN_GetProcessDpiAwareness)GetProcAddress(shcore,
+                                               "GetProcessDpiAwareness");
+
+  const PFN_GetScaleFactorForMonitor GetScaleFactorForMonitor =
+    (PFN_GetScaleFactorForMonitor)GetProcAddress(shcore,
+                                                 "GetScaleFactorForMonitor");
+
+  DWORD dpiAware    = 0;
+  DWORD scaleFactor = 100;
+  if (GetProcessDpiAwareness && GetScaleFactorForMonitor &&
+      !GetProcessDpiAwareness(NULL, &dpiAware) && dpiAware) {
+    GetScaleFactorForMonitor(
+      MonitorFromWindow(view->impl->hwnd, MONITOR_DEFAULTTOPRIMARY),
+      &scaleFactor);
+  }
+
+  FreeLibrary(shcore);
+  return (double)scaleFactor / 100.0;
+}
+
 PuglWorldInternals*
 puglInitWorldInternals(PuglWorldType type, PuglWorldFlags PUGL_UNUSED(flags))
 {
@@ -214,7 +245,8 @@ puglRealize(PuglView* view)
     puglSetWindowTitle(view, view->title);
   }
 
-  view->impl->cursor = LoadCursor(NULL, IDC_ARROW);
+  view->impl->scaleFactor = puglWinGetViewScaleFactor(view);
+  view->impl->cursor      = LoadCursor(NULL, IDC_ARROW);
 
   puglSetFrame(view, view->frame);
   SetWindowLongPtr(impl->hwnd, GWLP_USERDATA, (LONG_PTR)view);
@@ -604,6 +636,9 @@ handleMessage(PuglView* view, UINT message, WPARAM wParam, LPARAM lParam)
       InvalidateRect(view->impl->hwnd, NULL, false);
     }
     break;
+  case WM_DISPLAYCHANGE:
+    view->impl->scaleFactor = puglWinGetViewScaleFactor(view);
+    break;
   case WM_WINDOWPOSCHANGED:
     handleConfigure(view, &event);
     break;
@@ -1002,6 +1037,12 @@ adjustedWindowRect(PuglView* const view,
   return rect;
 }
 
+double
+puglGetScaleFactor(const PuglView* const view)
+{
+  return view->impl->scaleFactor;
+}
+
 PuglStatus
 puglSetFrame(PuglView* view, const PuglRect frame)
 {
diff --git a/src/win.h b/src/win.h
index 5c70e1e..f71dcf8 100644
--- a/src/win.h
+++ b/src/win.h
@@ -25,6 +25,7 @@ struct PuglInternalsImpl {
   HCURSOR      cursor;
   HDC          hdc;
   PuglSurface* surface;
+  double       scaleFactor;
   bool         flashing;
   bool         mouseTracked;
 };
diff --git a/src/x11.c b/src/x11.c
index 5ae6b12..c2e9e96 100644
--- a/src/x11.c
+++ b/src/x11.c
@@ -14,6 +14,7 @@
 #include <X11/X.h>
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
+#include <X11/Xresource.h>
 #include <X11/Xutil.h>
 #include <X11/keysym.h>
 
@@ -106,6 +107,33 @@ initXSync(PuglWorldInternals* const impl)
   return false;
 }
 
+static double
+puglX11GetDisplayScaleFactor(Display* const display)
+{
+  double            dpi = 96.0;
+  const char* const rms = XResourceManagerString(display);
+  if (rms) {
+    XrmDatabase db = XrmGetStringDatabase(rms);
+    if (db) {
+      XrmValue value = {0u, NULL};
+      char*    type  = NULL;
+      if (XrmGetResource(db, "Xft.dpi", "Xft.Dpi", &type, &value)) {
+        if (!type || !strcmp(type, "String")) {
+          char*        end    = NULL;
+          const double xftDpi = strtod(value.addr, &end);
+          if (xftDpi > 0.0 && xftDpi < HUGE_VAL) {
+            dpi = xftDpi;
+          }
+        }
+      }
+
+      XrmDestroyDatabase(db);
+    }
+  }
+
+  return dpi / 96.0;
+}
+
 PuglWorldInternals*
 puglInitWorldInternals(const PuglWorldType type, const PuglWorldFlags flags)
 {
@@ -121,7 +149,8 @@ puglInitWorldInternals(const PuglWorldType type, const PuglWorldFlags flags)
   PuglWorldInternals* impl =
     (PuglWorldInternals*)calloc(1, sizeof(PuglWorldInternals));
 
-  impl->display = display;
+  impl->display     = display;
+  impl->scaleFactor = puglX11GetDisplayScaleFactor(display);
 
   // Intern the various atoms we will need
   impl->atoms.CLIPBOARD        = XInternAtom(display, "CLIPBOARD", 0);
@@ -1367,6 +1396,12 @@ puglSetWindowTitle(PuglView* const view, const char* const title)
   return PUGL_SUCCESS;
 }
 
+double
+puglGetScaleFactor(const PuglView* const view)
+{
+  return view->world->impl->scaleFactor;
+}
+
 PuglStatus
 puglSetFrame(PuglView* const view, const PuglRect frame)
 {
diff --git a/src/x11.h b/src/x11.h
index 49a1d06..1be54ad 100644
--- a/src/x11.h
+++ b/src/x11.h
@@ -39,6 +39,7 @@ struct PuglWorldInternalsImpl {
   Display*     display;
   PuglX11Atoms atoms;
   XIM          xim;
+  double       scaleFactor;
   PuglTimer*   timers;
   size_t       numTimers;
   XID          serverTimeCounter;