From 60d33f28471d4fb247ebe8f8205211240b7c4382 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 28 Jun 2022 11:29:57 +0530
Subject: [PATCH] Wayland: Reduce flicker at startup by not using render frames
 immediately after a resize

Fixes #5235
---
 docs/changelog.rst    | 2 ++
 kitty/child-monitor.c | 6 ++++--
 kitty/glfw.c          | 4 +++-
 kitty/state.h         | 1 +
 4 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index b715fac0d..33d854b30 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -54,6 +54,8 @@ Detailed list of changes
 - macOS: Fix a regression that caused switching keyboard input using Eisu and
   Kana keys not working (:iss:`5232`)
 
+- Wayland: Reduce flicker at startup by not using render frames immediately after a resize (:iss:`5235`)
+
 
 0.25.2 [2022-06-07]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/kitty/child-monitor.c b/kitty/child-monitor.c
index 771e98547..de884346c 100644
--- a/kitty/child-monitor.c
+++ b/kitty/child-monitor.c
@@ -758,7 +758,6 @@ render(monotonic_t now, bool input_read) {
 
     for (size_t i = 0; i < global_state.num_os_windows; i++) {
         OSWindow *w = global_state.os_windows + i;
-        w->render_calls++;
         if (!w->num_tabs) continue;
         if (!should_os_window_be_rendered(w)) {
             update_os_window_title(w);
@@ -767,8 +766,11 @@ render(monotonic_t now, bool input_read) {
         }
         if (USE_RENDER_FRAMES && w->render_state != RENDER_FRAME_READY) {
             if (w->render_state == RENDER_FRAME_NOT_REQUESTED || no_render_frame_received_recently(w, now, ms_to_monotonic_t(250ll))) request_frame_render(w);
-            continue;
+            // dont respect render frames soon after a resize on Wayland as they cause flicker because
+            // we want to fill the newly resized buffer ASAP, not at compositors convenience
+            if (global_state.is_wayland && (monotonic() - w->viewport_resized_at) > s_double_to_monotonic_t(1)) continue;
         }
+        w->render_calls++;
         make_os_window_context_current(w);
         if (w->live_resize.in_progress && OPT(resize_draw_strategy) >= RESIZE_DRAW_BLANK) {
             blank_os_window(w);
diff --git a/kitty/glfw.c b/kitty/glfw.c
index d5e40fe2d..cbe543480 100644
--- a/kitty/glfw.c
+++ b/kitty/glfw.c
@@ -108,6 +108,7 @@ update_os_window_viewport(OSWindow *window, bool notify_boss) {
         return; // no change, ignore
     }
     int min_width, min_height; min_size_for_os_window(window, &min_width, &min_height);
+    window->viewport_resized_at = monotonic();
     if (w <= 0 || h <= 0 || fw < min_width || fh < min_height || fw < w || fh < h) {
         log_error("Invalid geometry ignored: framebuffer: %dx%d window: %dx%d\n", fw, fh, w, h);
         if (!window->viewport_updated_at_least_once) {
@@ -1356,7 +1357,8 @@ should_os_window_be_rendered(OSWindow* w) {
     return (
             glfwGetWindowAttrib(w->handle, GLFW_ICONIFIED) ||
             !glfwGetWindowAttrib(w->handle, GLFW_VISIBLE) ||
-            glfwGetWindowAttrib(w->handle, GLFW_OCCLUDED)
+            glfwGetWindowAttrib(w->handle, GLFW_OCCLUDED) ||
+            !glfwAreSwapsAllowed(w->handle)
        ) ? false : true;
 }
 
diff --git a/kitty/state.h b/kitty/state.h
index 21f42a019..ee38bfb4e 100644
--- a/kitty/state.h
+++ b/kitty/state.h
@@ -201,6 +201,7 @@ typedef struct {
     PyObject *window_title;
     bool disallow_title_changes, title_is_overriden;
     bool viewport_size_dirty, viewport_updated_at_least_once;
+    monotonic_t viewport_resized_at;
     LiveResizeInfo live_resize;
     bool has_pending_resizes, is_semi_transparent, shown_once, is_damaged;
     uint32_t offscreen_texture_id;