bug#46155: 28.0.50; Regression: buffer contents flicker on macOS frames when

[Alan Third <alan@idiocy.org>]

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On Thu, Jan 28, 2021 at 04:39:49PM +0000, Alan Third wrote:
> On Thu, Jan 28, 2021 at 09:48:25AM -0600, Aaron Jensen wrote:
> > From emacs -Q:
> > 
> > (dotimes (n 10)
> >   (set-frame-parameter nil 'width (+ 80 n))
> >   (sit-for 0.1))
> > 
> > This was previously fixed in bug#30699
> > 
> > I don't know if it was reverted at some point and I didn't notice, or it
> > was started flickering again after Alan's recent (fantastic) performance
> > improvements.
> > 
> > This reproduces on master (non-native-comp) as of ac102bb966 as well.
> 
> Apple deprecated the functions we were using to block screen drawing.
> 
> It's possible we can have a neater work-around now since we're drawing
> to an offscreen buffer and therefore have greater control over what's
> displayed. I'll have to look into it again.

Well... I tried something ridiculous and it appears to work...

I suspect forcing redisplay this way within the NS run loop is bad
form, but it appears to work.
-- 
Alan Third

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From ed901d4219b996a72e5944c6b959086ef2b8431d Mon Sep 17 00:00:00 2001
From: Alan Third <alan@idiocy.org>
Date: Sun, 31 Jan 2021 20:19:53 +0000
Subject: [PATCH] Fix flicker when resizing NS frame programmatically
 (bug#46155)

; Incidentally fixes bug#21326.

* src/nsterm.m ([EmacsView viewWillDraw]): New function.
---
 src/nsterm.m | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/nsterm.m b/src/nsterm.m
index 1b2328628e..8f2b61a165 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -8452,6 +8452,33 @@ - (void)copyRect:(NSRect)srcRect to:(NSRect)dstRect
 }
 
 
+#ifdef NS_IMPL_COCOA
+/* If the frame has been garbaged but the toolkit wants to draw, for
+   example when resizing the frame, we end up with a blank screen.
+   Sometimes this results in an unpleasant flicker, so try to
+   redisplay before drawing.  */
+- (void)viewWillDraw
+{
+  if (FRAME_GARBAGED_P (emacsframe))
+    {
+      /* If there is IO going on when redisplay is run here Emacs
+         crashes.  I think it's because this code will always be run
+         within the run loop and for whatever reason processing input
+         is dangerous.  This technique was stolen wholesale from
+         nsmenu.m and seems to work.  */
+      bool owfi = waiting_for_input;
+      waiting_for_input = 0;
+      block_input ();
+
+      redisplay();
+
+      unblock_input ();
+      waiting_for_input = owfi;
+    }
+}
+#endif
+
+
 #ifdef NS_DRAW_TO_BUFFER
 - (BOOL)wantsUpdateLayer
 {
-- 
2.29.2