Add `prefer_egl` debug option

Some systems have rendering issues when using GLX rather than EGL. While this is
usually due to a driver bug, it is helpful to provide a workaround for this by
allowing people to prefer EGL over GLX.

This patch adds the new `debug.prefer_egl` option to provide this workaround.

Closes #7056.

5 files changed, 28 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 776a7358..894c998e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Copy global IPC options (`-w -1`) for new windows
 - Bindings to create and navigate tabs on macOS
 - Support startup notify protocol to raise initial window on Wayland/X11
+- Debug option `prefer_egl` to prioritize EGL over other display APIs
 
 ### Changed
 
diff --git a/alacritty/src/config/debug.rs b/alacritty/src/config/debug.rs
index fe0c78f1..a8be77d9 100644
--- a/alacritty/src/config/debug.rs
+++ b/alacritty/src/config/debug.rs
@@ -23,6 +23,9 @@ pub struct Debug {
     /// The renderer alacritty should be using.
     pub renderer: Option<RendererPreference>,
 
+    /// Use EGL as display API if the current platform allows it.
+    pub prefer_egl: bool,
+
     /// Record ref test.
     #[config(skip)]
     pub ref_test: bool,
@@ -38,6 +41,7 @@ impl Default for Debug {
             highlight_damage: Default::default(),
             ref_test: Default::default(),
             renderer: Default::default(),
+            prefer_egl: Default::default(),
         }
     }
 }
diff --git a/alacritty/src/renderer/platform.rs b/alacritty/src/renderer/platform.rs
index 495e837e..b31e6974 100644
--- a/alacritty/src/renderer/platform.rs
+++ b/alacritty/src/renderer/platform.rs
@@ -21,15 +21,24 @@ use winit::window::raw_window_handle::{RawDisplayHandle, RawWindowHandle};
 pub fn create_gl_display(
     raw_display_handle: RawDisplayHandle,
     _raw_window_handle: Option<RawWindowHandle>,
+    _prefer_egl: bool,
 ) -> GlutinResult<Display> {
     #[cfg(target_os = "macos")]
     let preference = DisplayApiPreference::Cgl;
 
     #[cfg(windows)]
-    let preference = DisplayApiPreference::Wgl(Some(_raw_window_handle.unwrap()));
+    let preference = if _prefer_egl {
+        DisplayApiPreference::EglThenWgl(Some(_raw_window_handle.unwrap()))
+    } else {
+        DisplayApiPreference::WglThenEgl(Some(_raw_window_handle.unwrap()))
+    };
 
     #[cfg(all(feature = "x11", not(any(target_os = "macos", windows))))]
-    let preference = DisplayApiPreference::GlxThenEgl(Box::new(x11::register_xlib_error_hook));
+    let preference = if _prefer_egl {
+        DisplayApiPreference::EglThenGlx(Box::new(x11::register_xlib_error_hook))
+    } else {
+        DisplayApiPreference::GlxThenEgl(Box::new(x11::register_xlib_error_hook))
+    };
 
     #[cfg(all(not(feature = "x11"), not(any(target_os = "macos", windows))))]
     let preference = DisplayApiPreference::Egl;
diff --git a/alacritty/src/window_context.rs b/alacritty/src/window_context.rs
index 84ce4457..332bdcd9 100644
--- a/alacritty/src/window_context.rs
+++ b/alacritty/src/window_context.rs
@@ -92,8 +92,11 @@ impl WindowContext {
         #[cfg(not(windows))]
         let raw_window_handle = None;
 
-        let gl_display =
-            renderer::platform::create_gl_display(raw_display_handle, raw_window_handle)?;
+        let gl_display = renderer::platform::create_gl_display(
+            raw_display_handle,
+            raw_window_handle,
+            config.debug.prefer_egl,
+        )?;
         let gl_config = renderer::platform::pick_gl_config(&gl_display, raw_window_handle)?;
 
         #[cfg(not(windows))]
diff --git a/extra/man/alacritty.5.scd b/extra/man/alacritty.5.scd
index 8d44e019..bc2c04f1 100644
--- a/extra/man/alacritty.5.scd
+++ b/extra/man/alacritty.5.scd
@@ -935,6 +935,13 @@ relied upon.
 
 	Default: _false_
 
+*prefer_egl* <boolean>
+
+    Use EGL as display API if the current platform allows it. Note that
+    transparency may not work with EGL on Linux/BSD.
+
+    Default: _false_
+
 # SEE ALSO
 
 *alacritty*(1), *alacritty-msg*(1), *alacritty-bindings*(5)