From bd44e82ecaefbd2056eeb58bba48209b94b28c75 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Fri, 22 Oct 2021 18:07:14 +0200
Subject: [PATCH] =?UTF-8?q?bar/wayland:=20coalesce=20=E2=80=9Crefresh?=
 =?UTF-8?q?=E2=80=9D=20commands?=
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This reduces the number of repaints primarily during startup, but also
when e.g. switching workspace.
---
 bar/wayland.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/bar/wayland.c b/bar/wayland.c
index 02e9ad6..90d1103 100644
--- a/bar/wayland.c
+++ b/bar/wayland.c
@@ -7,6 +7,7 @@
 #include <unistd.h>
 #include <poll.h>
 #include <pthread.h>
+#include <errno.h>
 
 #include <sys/mman.h>
 #include <fcntl.h>
@@ -1139,16 +1140,30 @@ loop(struct bar *_bar,
         }
 
         if (fds[2].revents & POLLIN) {
-            uint8_t command;
-            if (read(backend->pipe_fds[0], &command, sizeof(command))
-                != sizeof(command))
-            {
-                LOG_ERRNO("failed to read from command pipe");
-                break;
+            bool do_expose = false;
+
+            /* Coalesce “refresh” commands */
+            size_t count = 0;
+            while (true) {
+                uint8_t command;
+                ssize_t r = read(backend->pipe_fds[0], &command, sizeof(command));
+                if (r < 0 && errno == EAGAIN)
+                    break;
+                if (r != sizeof(command)) {
+                    LOG_ERRNO("failed to read from command pipe");
+                    break;
+                }
+
+                assert(command == 1);
+                if (command == 1) {
+                    count++;
+                    do_expose = true;
+                }
             }
 
-            assert(command == 1);
-            expose(_bar);
+            LOG_DBG("coalesced %zu expose commands", count);
+            if (do_expose)
+                expose(_bar);
         }
 
         if (fds[1].revents & POLLIN) {