From 7929e0bc09d4524d982c6ac369013eba40762fd0 Mon Sep 17 00:00:00 2001
From: Qwerasd <qwerasd205@users.noreply.github.com>
Date: Wed, 14 Aug 2024 19:35:52 -0400
Subject: [PATCH] fix: prevent flicker while shrinking screen by eliminating
 thread race

Before this fix, if vsync was on the GPU cells buffer could be cleared
for a frame while resizing the terminal down. This was due to the fact
that the surface sent messages for the resize to both the renderer and
the IO thread. If the renderer thread was processed first then the GPU
cells buffer(s) would be cleared and not rebuilt, because the terminal
state would be larger than the GPU cell buffers causing updateFrame to
bail out early, leaving empty cell buffers.

This fixes the problem by changing the origin of the renderer's resize
message to be the IO thread, only after properly updating the terminal
state, to avoid clearing the GPU cells buffers at a time they can't be
successfully rebuilt.
---
 src/Surface.zig         |  9 ---------
 src/renderer/Metal.zig  | 10 ++++++----
 src/renderer/Thread.zig |  6 +++---
 src/termio/Termio.zig   |  8 +++++++-
 4 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/src/Surface.zig b/src/Surface.zig
index 2e283f985..fc3144ade 100644
--- a/src/Surface.zig
+++ b/src/Surface.zig
@@ -1197,15 +1197,6 @@ fn resize(self: *Surface, size: renderer.ScreenSize) !void {
     // Save our screen size
     self.screen_size = size;
 
-    // Mail the renderer so that it can update the GPU and re-render
-    _ = self.renderer_thread.mailbox.push(.{
-        .resize = .{
-            .screen_size = self.screen_size,
-            .padding = self.padding,
-        },
-    }, .{ .forever = {} });
-    try self.queueRender();
-
     // Recalculate our grid size. Because Ghostty supports fluid resizing,
     // its possible the grid doesn't change at all even if the screen size changes.
     // We have to update the IO thread no matter what because we send
diff --git a/src/renderer/Metal.zig b/src/renderer/Metal.zig
index ebd5d9b0d..4f669d474 100644
--- a/src/renderer/Metal.zig
+++ b/src/renderer/Metal.zig
@@ -2012,11 +2012,13 @@ pub fn setScreenSize(
         .cursor_color = old.cursor_color,
     };
 
-    // Reset our cell contents.
-    try self.cells.resize(self.alloc, grid_size);
+    // Reset our cell contents if our grid size has changed.
+    if (!self.cells.size.equals(grid_size)) {
+        try self.cells.resize(self.alloc, grid_size);
 
-    // Reset our viewport to force a rebuild
-    self.cells_viewport = null;
+        // Reset our viewport to force a rebuild
+        self.cells_viewport = null;
+    }
 
     // If we have custom shaders then we update the state
     if (self.custom_shader_state) |*state| {
diff --git a/src/renderer/Thread.zig b/src/renderer/Thread.zig
index 459fc105a..2725a2175 100644
--- a/src/renderer/Thread.zig
+++ b/src/renderer/Thread.zig
@@ -480,7 +480,7 @@ fn drawCallback(
     r: xev.Timer.RunError!void,
 ) xev.CallbackAction {
     _ = r catch unreachable;
-    const t = self_ orelse {
+    const t: *Thread = self_ orelse {
         // This shouldn't happen so we log it.
         log.warn("render callback fired without data set", .{});
         return .disarm;
@@ -504,7 +504,7 @@ fn renderCallback(
     r: xev.Timer.RunError!void,
 ) xev.CallbackAction {
     _ = r catch unreachable;
-    const t = self_ orelse {
+    const t: *Thread = self_ orelse {
         // This shouldn't happen so we log it.
         log.warn("render callback fired without data set", .{});
         return .disarm;
@@ -543,7 +543,7 @@ fn cursorTimerCallback(
         },
     };
 
-    const t = self_ orelse {
+    const t: *Thread = self_ orelse {
         // This shouldn't happen so we log it.
         log.warn("render callback fired without data set", .{});
         return .disarm;
diff --git a/src/termio/Termio.zig b/src/termio/Termio.zig
index 246b9b2f8..7573b000b 100644
--- a/src/termio/Termio.zig
+++ b/src/termio/Termio.zig
@@ -378,7 +378,13 @@ pub fn resize(
         // immediately for a resize. This is allowed by the spec.
         self.terminal.modes.set(.synchronized_output, false);
 
-        // Wake up our renderer so any changes will be shown asap
+        // Mail the renderer so that it can update the GPU and re-render
+        _ = self.renderer_mailbox.push(.{
+            .resize = .{
+                .screen_size = screen_size,
+                .padding = padding,
+            },
+        }, .{ .forever = {} });
         self.renderer_wakeup.notify() catch {};
 
         // If we have size reporting enabled we need to send a report.