--- utils/viewer-cocoa.m	2026-03-23 09:54:26.000000000 +0800
+++ utils/viewer-cocoa.m	2026-05-06 21:55:28.000000000 +0800
@@ -18,7 +18,9 @@
  * Boston, MA 02111-1307, USA.
  */
 #include "config.h"
-#import <Cocoa/Cocoa.h>
+
+#include <strings.h> /* bzero */
+#include <Cocoa/Cocoa.h>
 
 #include <cairo.h>
 #include <cairo-quartz.h>
@@ -28,33 +30,91 @@
 #include "viewer-cocoa.h"
 #include "viewer-cocoa-resources.h"
 
+/* Compatibility shims for renamed constants (macOS 10.12+) */
+#ifndef NSWindowStyleMaskTitled
+# define NSWindowStyleMaskTitled    NSTitledWindowMask
+# define NSWindowStyleMaskClosable  NSClosableWindowMask
+#endif
+#ifndef NSEventMaskAny
+# define NSEventMaskAny NSAnyEventMask
+#endif
+#ifndef NSEventTypeKeyDown
+# define NSEventTypeKeyDown NSKeyDown
+#endif
+
+/* Forward-declare methods that were added after the 10.6 SDK so that
+ * GCC (which does not auto-import newer SDK declarations) knows their
+ * return types when we call them behind a -respondsToSelector: guard.
+ * Under clang with a modern SDK these categories are harmless no-ops. */
+#if MAC_OS_X_VERSION_MAX_ALLOWED < 101000
+@interface NSGraphicsContext (PangoCGContextAccessor)
+- (CGContextRef)CGContext;
+@end
+#endif
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED < 1070
+@interface NSWindow (PangoBackingScaleFactor)
+- (CGFloat)backingScaleFactor;
+@end
+#endif
+
 struct _CocoaViewer
 {
   NSApplication *app;
 };
 
 @interface PangoView : NSView
+{
+  cairo_surface_t *_surface;  /* explicit ivar required by GCC */
+}
 
-@property (nonatomic, assign, nullable) cairo_surface_t *surface;
+/* 'nullable' is a clang nullability annotation added in Xcode 7 (clang 6.1).
+ * Omit it so the code compiles with older toolchains. */
+@property (nonatomic, assign) cairo_surface_t *surface;
 
 @end
 
 @implementation PangoView
 
+/* GCC does not auto-synthesize @property; clang does.
+ * This directive is a no-op on clang with a modern runtime. */
+@synthesize surface = _surface;
+
 - (void)drawRect:(NSRect)dirtyRect
 {
   if ([self surface])
   {
     NSGraphicsContext *context = [NSGraphicsContext currentContext];
-    CGContextRef cgContext = [context CGContext];
-    CGFloat scaleFactor = [[self window] backingScaleFactor];
+    CGContextRef cgContext;
+
+    /* -[NSGraphicsContext CGContext] is macOS 10.10+.
+     * Fall back to the deprecated -graphicsPort on older systems. */
+    if ([context respondsToSelector:@selector(CGContext)])
+      cgContext = [context CGContext];
+    else
+      {
+#ifdef __clang__
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#endif
+        cgContext = (CGContextRef)[context graphicsPort];
+#ifdef __clang__
+# pragma clang diagnostic pop
+#endif
+      }
+
+    /* -[NSWindow backingScaleFactor] is macOS 10.7+.
+     * On 10.6 there is no HiDPI so 1.0 is correct. */
+    CGFloat scaleFactor = 1.0;
+    if ([[self window] respondsToSelector:@selector(backingScaleFactor)])
+      scaleFactor = [[self window] backingScaleFactor];
 
     CGContextTranslateCTM (cgContext, 0.0, [self bounds].size.height);
     CGContextScaleCTM (cgContext, 1/scaleFactor, -1/scaleFactor);
 
     cairo_surface_t *viewSurface = cairo_quartz_surface_create_for_cg_context (cgContext,
-									       [self bounds].size.width * scaleFactor,
-									       [self bounds].size.height * scaleFactor);
+                                                                               [self bounds].size.width * scaleFactor,
+                                                                               [self bounds].size.height * scaleFactor);
 
     cairo_surface_set_device_scale (viewSurface, scaleFactor, scaleFactor);
     cairo_t *cr = cairo_create (viewSurface);