Allow dynamic choice of drawing path on NS (bug#39883)

* src/nsterm.h (NS_DRAW_TO_BUFFER): Let this be enabled on versions
older than 10.14.
* src/nsterm.m (ns_update_begin):
(ns_update_end):
(ns_focus):
(ns_unfocus):
([EmacsView viewDidResize:]):
([EmacsView createDrawingBuffer]):
([EmacsView windowDidChangeBackingProperties:]):
([EmacsView copyRect:to:]):
([EmacsView wantsUpdateLayer]): Dynamically switch between drawing to a
buffer and drawing to the screen, depending on the version of AppKit
in use.
([EmacsView dealloc]): We can't release the context unless
NS_DRAW_TO_BUFFER is defined.

2 files changed, 167 insertions, 72 deletions

diff --git a/src/nsterm.h b/src/nsterm.h
index e142dbd4f07..f5d3c32b8b3 100644
--- a/src/nsterm.h
+++ b/src/nsterm.h
@@ -343,14 +343,8 @@ typedef id instancetype;
    therefore we draw to an offscreen buffer and swap it in when the
    toolkit wants to draw the frame. GNUstep and macOS 10.7 and below
    do not support this method, so we revert to drawing directly to the
-   glass.
-
-   FIXME: Should we make this macOS 10.8+, or macOS 10.14+?  I'm
-   inclined to go with 10.14+ as there have been some reports of funny
-   behaviour on 10.13 and below.  It may be worth adding a variable to
-   allow people in the overlapping region to switch between drawing
-   paths.  */
-#if defined (NS_IMPL_COCOA) && defined (MAC_OS_X_VERSION_10_14)
+   glass.  */
+#if defined (NS_IMPL_COCOA) && MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
 #define NS_DRAW_TO_BUFFER 1
 #endif
 
diff --git a/src/nsterm.m b/src/nsterm.m
index a75c3ef4dba..9cd1c9d8602 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -1144,10 +1144,25 @@ ns_update_begin (struct frame *f)
 
   ns_updating_frame = f;
 #ifdef NS_DRAW_TO_BUFFER
-  [view focusOnDrawingBuffer];
-#else
-  [view lockFocus];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if ([FRAME_NS_VIEW (f) wantsUpdateLayer])
+    {
 #endif
+      [view focusOnDrawingBuffer];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+  else
+    {
+#endif
+#endif /* NS_DRAW_TO_BUFFER */
+
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      [view lockFocus];
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+#endif
+
 }
 
 
@@ -1166,15 +1181,29 @@ ns_update_end (struct frame *f)
   MOUSE_HL_INFO (f)->mouse_face_defer = 0;
 
 #ifdef NS_DRAW_TO_BUFFER
-  [NSGraphicsContext setCurrentContext:nil];
-  [view setNeedsDisplay:YES];
-#else
-  block_input ();
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if ([FRAME_NS_VIEW (f) wantsUpdateLayer])
+    {
+#endif
+      [NSGraphicsContext setCurrentContext:nil];
+      [view setNeedsDisplay:YES];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+  else
+    {
+#endif
+#endif /* NS_DRAW_TO_BUFFER */
 
-  [view unlockFocus];
-  [[view window] flushWindow];
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      block_input ();
 
-  unblock_input ();
+      [view unlockFocus];
+      [[view window] flushWindow];
+
+      unblock_input ();
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
 #endif
   ns_updating_frame = NULL;
 }
@@ -1199,24 +1228,39 @@ ns_focus (struct frame *f, NSRect *r, int n)
     }
 
   if (f != ns_updating_frame)
-#ifdef NS_DRAW_TO_BUFFER
-    [view focusOnDrawingBuffer];
-#else
     {
-      if (view != focus_view)
+#ifdef NS_DRAW_TO_BUFFER
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      if ([FRAME_NS_VIEW (f) wantsUpdateLayer])
         {
-          if (focus_view != NULL)
+#endif
+          [view focusOnDrawingBuffer];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+        }
+      else
+        {
+#endif
+#endif /* NS_DRAW_TO_BUFFER */
+
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+          if (view != focus_view)
             {
-              [focus_view unlockFocus];
-              [[focus_view window] flushWindow];
-            }
+              if (focus_view != NULL)
+                {
+                  [focus_view unlockFocus];
+                  [[focus_view window] flushWindow];
+                }
 
-          if (view)
-            [view lockFocus];
-          focus_view = view;
+              if (view)
+                [view lockFocus];
+              focus_view = view;
+            }
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
         }
-    }
 #endif
+    }
+
 
   /* clipping */
   if (r)
@@ -1246,16 +1290,30 @@ ns_unfocus (struct frame *f)
     }
 
 #ifdef NS_DRAW_TO_BUFFER
-  [FRAME_NS_VIEW (f) setNeedsDisplay:YES];
-#else
-  if (f != ns_updating_frame)
+  #if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if ([FRAME_NS_VIEW (f) wantsUpdateLayer])
+    {
+#endif
+      [FRAME_NS_VIEW (f) setNeedsDisplay:YES];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+  else
     {
-      if (focus_view != NULL)
+#endif
+#endif /* NS_DRAW_TO_BUFFER */
+
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      if (f != ns_updating_frame)
         {
-          [focus_view unlockFocus];
-          [[focus_view window] flushWindow];
-          focus_view = NULL;
+          if (focus_view != NULL)
+            {
+              [focus_view unlockFocus];
+              [[focus_view window] flushWindow];
+              focus_view = NULL;
+            }
         }
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
     }
 #endif
 }
@@ -6254,7 +6312,9 @@ not_in_argv (NSString *arg)
               name:NSViewFrameDidChangeNotification
             object:nil];
 
+#ifdef NS_DRAW_TO_BUFFER
   CGContextRelease (drawingBuffer);
+#endif
 
   [toolbar release];
   if (fs_state == FULLSCREEN_BOTH)
@@ -7268,13 +7328,27 @@ not_in_argv (NSString *arg)
     return;
 
 #ifdef NS_DRAW_TO_BUFFER
-  CGFloat scale = [[self window] backingScaleFactor];
-  oldw = (CGFloat)CGBitmapContextGetWidth (drawingBuffer) / scale;
-  oldh = (CGFloat)CGBitmapContextGetHeight (drawingBuffer) / scale;
-#else
-  oldw = FRAME_PIXEL_WIDTH (emacsframe);
-  oldh = FRAME_PIXEL_HEIGHT (emacsframe);
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if ([self wantsUpdateLayer])
+    {
+#endif
+      CGFloat scale = [[self window] backingScaleFactor];
+      oldw = (CGFloat)CGBitmapContextGetWidth (drawingBuffer) / scale;
+      oldh = (CGFloat)CGBitmapContextGetHeight (drawingBuffer) / scale;
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+  else
+    {
 #endif
+#endif /* NS_DRAW_TO_BUFFER */
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      oldw = FRAME_PIXEL_WIDTH (emacsframe);
+      oldh = FRAME_PIXEL_HEIGHT (emacsframe);
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+#endif
+
   neww = (int)NSWidth (frame);
   newh = (int)NSHeight (frame);
 
@@ -8304,6 +8378,9 @@ not_in_argv (NSString *arg)
 {
   NSTRACE ("EmacsView createDrawingBuffer]");
 
+  if (! [self wantsUpdateLayer])
+    return;
+
   NSGraphicsContext *screen;
   CGColorSpaceRef colorSpace = [[[self window] colorSpace] CGColorSpace];
   CGFloat scale = [[self window] backingScaleFactor];
@@ -8339,6 +8416,9 @@ not_in_argv (NSString *arg)
 {
   NSTRACE ("EmacsView windowDidChangeBackingProperties:]");
 
+  if (! [self wantsUpdateLayer])
+    return;
+
   CGFloat old = [[[notification userInfo]
                     objectForKey:@"NSBackingPropertyOldScaleFactorKey"]
                   doubleValue];
@@ -8362,41 +8442,56 @@ not_in_argv (NSString *arg)
   NSTRACE_RECT ("Destination", dstRect);
 
 #ifdef NS_DRAW_TO_BUFFER
-  CGImageRef copy;
-  NSRect frame = [self frame];
-  NSAffineTransform *setOrigin = [NSAffineTransform transform];
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if ([self wantsUpdateLayer])
+    {
+#endif
+      CGImageRef copy;
+      NSRect frame = [self frame];
+      NSAffineTransform *setOrigin = [NSAffineTransform transform];
 
-  [[NSGraphicsContext currentContext] saveGraphicsState];
+      [[NSGraphicsContext currentContext] saveGraphicsState];
 
-  /* Set the clipping before messing with the buffer's
-     orientation.  */
-  NSRectClip (dstRect);
+      /* Set the clipping before messing with the buffer's
+         orientation.  */
+      NSRectClip (dstRect);
 
-  /* Unflip the buffer as the copied image will be unflipped, and
-     offset the top left so when we draw back into the buffer the
-     correct part of the image is drawn.  */
-  CGContextScaleCTM(drawingBuffer, 1, -1);
-  CGContextTranslateCTM(drawingBuffer,
-                        NSMinX (dstRect) - NSMinX (srcRect),
-                        -NSHeight (frame) - (NSMinY (dstRect) - NSMinY (srcRect)));
+      /* Unflip the buffer as the copied image will be unflipped, and
+         offset the top left so when we draw back into the buffer the
+         correct part of the image is drawn.  */
+      CGContextScaleCTM(drawingBuffer, 1, -1);
+      CGContextTranslateCTM(drawingBuffer,
+                            NSMinX (dstRect) - NSMinX (srcRect),
+                            -NSHeight (frame) - (NSMinY (dstRect) - NSMinY (srcRect)));
 
-  /* Take a copy of the buffer and then draw it back to the buffer,
-     limited by the clipping rectangle.  */
-  copy = CGBitmapContextCreateImage (drawingBuffer);
-  CGContextDrawImage (drawingBuffer, frame, copy);
+      /* Take a copy of the buffer and then draw it back to the buffer,
+         limited by the clipping rectangle.  */
+      copy = CGBitmapContextCreateImage (drawingBuffer);
+      CGContextDrawImage (drawingBuffer, frame, copy);
 
-  CGImageRelease (copy);
+      CGImageRelease (copy);
 
-  [[NSGraphicsContext currentContext] restoreGraphicsState];
-  [self setNeedsDisplayInRect:dstRect];
-#else
-  hide_bell();              // Ensure the bell image isn't scrolled.
+      [[NSGraphicsContext currentContext] restoreGraphicsState];
+      [self setNeedsDisplayInRect:dstRect];
 
-  ns_focus (emacsframe, &dstRect, 1);
-  [self scrollRect: srcRect
-                by: NSMakeSize (dstRect.origin.x - srcRect.origin.x,
-                                dstRect.origin.y - srcRect.origin.y)];
-  ns_unfocus (emacsframe);
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
+  else
+    {
+#endif
+#endif /* NS_DRAW_TO_BUFFER */
+
+#if !defined (NS_DRAW_TO_BUFFER) || MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+      hide_bell();              // Ensure the bell image isn't scrolled.
+
+      ns_focus (emacsframe, &dstRect, 1);
+      [self scrollRect: srcRect
+                    by: NSMakeSize (dstRect.origin.x - srcRect.origin.x,
+                                    dstRect.origin.y - srcRect.origin.y)];
+      ns_unfocus (emacsframe);
+#endif
+#if defined (NS_DRAW_TO_BUFFER) && MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+    }
 #endif
 }
 
@@ -8404,7 +8499,13 @@ not_in_argv (NSString *arg)
 #ifdef NS_DRAW_TO_BUFFER
 - (BOOL)wantsUpdateLayer
 {
-    return YES;
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 101400
+  if (NSAppKitVersionNumber < 1671)
+    return NO;
+#endif
+
+  /* Running on macOS 10.14 or above.  */
+  return YES;
 }