From 1235daff045c0cb843966d318a922fd319829557 Mon Sep 17 00:00:00 2001
From: martinezhermes <hermes.martinez@doctolib.com>
Date: Fri, 20 Mar 2026 09:48:12 +0100
Subject: [PATCH] fix: apply background-opacity and background-blur to terminal
 rendering area

Two root causes for issue #879:

1. GhosttyNSView was missing makeBackingLayer(), so AppKit provided a
   generic CALayer as the view's backing layer. libghostty expects
   (view.layer as? CAMetalLayer) != nil to set up Metal rendering on
   the existing layer. Without a CAMetalLayer backing layer, the Metal
   surface defaulted to isOpaque=true, making the terminal area fully
   opaque regardless of background-opacity config.

   Fix: override makeBackingLayer() to return a CAMetalLayer with
   isOpaque=false and bgra8Unorm pixel format (matching standalone
   Ghostty's SurfaceView behavior).

2. ghostty_set_window_background_blur(app, window) is exposed in
   ghostty.h but was never called in cmux. Without this call the
   macOS window never gets the NSVisualEffectView blur backdrop that
   background-blur requires.

   Fix: add applyWindowBlurIfNeeded() on GhosttyApp that reads
   background-blur from config via ghostty_config_get and calls
   ghostty_set_window_background_blur when the value is non-zero.
   Called from applyBackgroundToKeyWindow() and
   applyWindowBackgroundIfActive() whenever the window is made
   transparent.

Fixes #879

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 Sources/GhosttyTerminalView.swift | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Sources/GhosttyTerminalView.swift b/Sources/GhosttyTerminalView.swift
index 17fe87ab..a6ac27fe 100644
--- a/Sources/GhosttyTerminalView.swift
+++ b/Sources/GhosttyTerminalView.swift
@@ -2411,6 +2411,7 @@ class GhosttyApp {
         if cmuxShouldUseClearWindowBackground(for: defaultBackgroundOpacity) {
             window.backgroundColor = cmuxTransparentWindowBaseColor()
             window.isOpaque = false
+            applyWindowBlurIfNeeded(window)
             if backgroundLogEnabled {
                 logBackground("applied transparent window background opacity=\(String(format: "%.3f", defaultBackgroundOpacity))")
             }
@@ -2424,6 +2425,16 @@ class GhosttyApp {
         }
     }
 
+    func applyWindowBlurIfNeeded(_ window: NSWindow) {
+        guard let app = self.app else { return }
+        // ghostty_set_window_background_blur reads background-blur and
+        // background-opacity from the app config internally and calls
+        // CGSSetWindowBackgroundBlurRadius — a compositor-level setter that is
+        // idempotent.  It is a no-op when opacity >= 1.0 or blur is disabled,
+        // so we can call it unconditionally whenever the window is transparent.
+        ghostty_set_window_background_blur(app, Unmanaged.passUnretained(window).toOpaque())
+    }
+
     private func activeMainWindow() -> NSWindow? {
         let keyWindow = NSApp.keyWindow
         if let raw = keyWindow?.identifier?.rawValue,
@@ -3849,6 +3860,18 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
         setup()
     }
 
+    override func makeBackingLayer() -> CALayer {
+        let metalLayer = CAMetalLayer()
+        metalLayer.pixelFormat = .bgra8Unorm
+        metalLayer.isOpaque = false
+        // framebufferOnly=false lets the macOS compositor read the drawable
+        // when blending translucent or blurred window layers.  This matches
+        // standalone Ghostty's SurfaceView and is required for background-opacity
+        // and background-blur to render correctly.
+        metalLayer.framebufferOnly = false
+        return metalLayer
+    }
+
     private func setup() {
         // Only enable our instrumented CAMetalLayer in targeted debug/test scenarios.
         // The lock in GhosttyMetalLayer.nextDrawable() adds overhead we don't want in normal runs.
@@ -3931,6 +3954,7 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
         if cmuxShouldUseClearWindowBackground(for: color.alphaComponent) {
             window.backgroundColor = cmuxTransparentWindowBaseColor()
             window.isOpaque = false
+            GhosttyApp.shared.applyWindowBlurIfNeeded(window)
         } else {
             window.backgroundColor = color
             window.isOpaque = color.alphaComponent >= 1.0