windows: Software frontend is now mesa llvmpipe

This is a bit of a switch-up, see this comment for more background:
refs: https://github.com/wez/wezterm/issues/265#issuecomment-701882933

This commit:

* Adds a pre-compiled mesa3d opengl32.dll replacement
* The mesa dll is deployed to `<appdir>/mesa/opengl32.dll` which by
  default is ignored.
* When the frontend is set to `Software` then the `mesa` directory
  is added to the dll search path, causing the llvmpipe renderer
  to be enabled.
* The old software renderer implementation is available using the
  `OldSoftware` frontend name

I'm not a huge fan of the subdirectory for the opengl32.dll, but
I couldn't get it to work under a different dll name; the code
thought that everything was initialized, but the window just rendered
a white rectangle.

Cargo.toml

@@ -8,6 +8,7 @@ default-run = "wezterm"
 
 [build-dependencies]
 vergen = "3"
+anyhow = "1.0"
 
 [target.'cfg(windows)'.build-dependencies]
 embed-resource = "1.3"

assets/windows/mesa/README.md

@@ -0,0 +1,6 @@
+This is a pre-built opendl32.dll for 64-bit Windows systems.
+It was obtained from <http://mesa.fdossena.com/>
+
+Mesa's License text can be found here:
+https://docs.mesa3d.org/license.html
+(a mixture of largely MITish licenses)

build.rs

@@ -1,3 +1,4 @@
+use anyhow::Context as _;
 use std::path::Path;
 use vergen::{generate_cargo_keys, ConstantsFlags};
 
@@ -81,7 +82,29 @@ fn main() {
             let src_name = conhost_dir.join(name);
 
             if !dest_name.exists() {
-                std::fs::copy(src_name, dest_name).unwrap();
+                std::fs::copy(&src_name, &dest_name)
+                    .context(format!(
+                        "copy {} -> {}",
+                        src_name.display(),
+                        dest_name.display()
+                    ))
+                    .unwrap();
+            }
+        }
+
+        {
+            let dest_mesa = exe_output_dir.join("mesa");
+            let _ = std::fs::create_dir(&dest_mesa);
+            let dest_name = dest_mesa.join("opengl32.dll");
+            let src_name = windows_dir.join("mesa").join("opengl32.dll");
+            if !dest_name.exists() {
+                std::fs::copy(&src_name, &dest_name)
+                    .context(format!(
+                        "copy {} -> {}",
+                        src_name.display(),
+                        dest_name.display()
+                    ))
+                    .unwrap();
             }
         }
 

ci/deploy.sh

@@ -52,6 +52,9 @@ case $OSTYPE in
       assets/windows/conhost/conpty.dll \
       assets/windows/conhost/OpenConsole.exe \
       $zipdir
+    mkdir $zipdir/mesa
+    cp $TARGET_DIR/release/mesa/opengl32.dll \
+        $zipdir/mesa
     7z a -tzip $zipname $zipdir
     iscc.exe -DMyAppVersion=${TAG_NAME#nightly} -F${instname} ci/windows-installer.iss
     ;;

ci/windows-installer.iss

@@ -43,6 +43,7 @@ Name: "desktopicon"; Description: "{cm:CreateDesktopIcon}"; GroupDescription: "{
 
 [Files]
 Source: "..\target\release\wezterm.exe"; DestDir: "{app}"; Flags: ignoreversion
+Source: "..\target\release\mesa\opengl32.dll"; DestDir: "{app}\mesa"; Flags: ignoreversion
 Source: "..\target\release\conpty.dll"; DestDir: "{app}"; Flags: ignoreversion
 Source: "..\target\release\OpenConsole.exe"; DestDir: "{app}"; Flags: ignoreversion
 Source: "..\target\release\strip-ansi-escapes.exe"; DestDir: "{app}"; Flags: ignoreversion

src/frontend/gui/mod.rs

@@ -42,6 +42,11 @@ impl GuiFrontEnd {
         Self::try_new()
     }
 
+    pub fn try_new_swrast() -> anyhow::Result<Rc<dyn FrontEnd>> {
+        ::window::prefer_swrast();
+        Self::try_new()
+    }
+
     pub fn try_new() -> anyhow::Result<Rc<dyn FrontEnd>> {
         #[cfg(all(unix, not(target_os = "macos")))]
         {
@@ -49,6 +54,7 @@ impl GuiFrontEnd {
                 Connection::disable_wayland();
             }
         }
+
         let connection = Connection::init()?;
         let front_end = Rc::new(GuiFrontEnd { connection });
         Ok(front_end)

src/frontend/mod.rs

@@ -16,6 +16,7 @@ pub mod muxserver;
 pub enum FrontEndSelection {
     OpenGL,
     Software,
+    OldSoftware,
     MuxServer,
     Null,
 }
@@ -59,7 +60,8 @@ impl FrontEndSelection {
         let (front_end, is_gui) = match self {
             FrontEndSelection::MuxServer => (muxserver::MuxServerFrontEnd::try_new(), false),
             FrontEndSelection::Null => (muxserver::MuxServerFrontEnd::new_null(), false),
-            FrontEndSelection::Software => (gui::GuiFrontEnd::try_new_no_opengl(), true),
+            FrontEndSelection::Software => (gui::GuiFrontEnd::try_new_swrast(), true),
+            FrontEndSelection::OldSoftware => (gui::GuiFrontEnd::try_new_no_opengl(), true),
             FrontEndSelection::OpenGL => (gui::GuiFrontEnd::try_new(), true),
         };
 
@@ -73,7 +75,7 @@ impl FrontEndSelection {
 
     // TODO: find or build a proc macro for this
     pub fn variants() -> Vec<&'static str> {
-        vec!["OpenGL", "Software", "MuxServer", "Null"]
+        vec!["OpenGL", "Software", "OldSoftware", "MuxServer", "Null"]
     }
 }
 
@@ -84,6 +86,7 @@ impl std::str::FromStr for FrontEndSelection {
             "muxserver" => Ok(FrontEndSelection::MuxServer),
             "null" => Ok(FrontEndSelection::Null),
             "software" => Ok(FrontEndSelection::Software),
+            "oldsoftware" => Ok(FrontEndSelection::OldSoftware),
             "opengl" => Ok(FrontEndSelection::OpenGL),
             _ => Err(anyhow!(
                 "{} is not a valid FrontEndSelection variant, possible values are {:?}",

window/src/lib.rs

@@ -1,5 +1,6 @@
 use promise::Future;
 use std::any::Any;
+use std::sync::atomic::{AtomicBool, Ordering};
 pub mod bitmaps;
 pub mod color;
 pub mod connection;
@@ -292,3 +293,13 @@ pub trait WindowOpsMut {
     /// and/or in the task manager/task switcher
     fn set_icon(&mut self, _image: &dyn BitmapImage) {}
 }
+
+static PREFER_SWRAST: AtomicBool = AtomicBool::new(false);
+
+pub fn prefer_swrast() {
+    PREFER_SWRAST.store(true, Ordering::Release);
+}
+
+pub fn is_swrast_preferred() -> bool {
+    PREFER_SWRAST.load(Ordering::Acquire)
+}

window/src/os/windows/wgl.rs

@@ -1,6 +1,7 @@
 #![cfg(feature = "opengl")]
 
 use super::*;
+use crate::is_swrast_preferred;
 use glium::backend::Backend;
 use std::ffi::CStr;
 use std::io::Error as IoError;
@@ -8,6 +9,7 @@ use std::os::raw::c_void;
 use std::ptr::{null, null_mut};
 use winapi::shared::windef::*;
 use winapi::um::libloaderapi::GetModuleHandleW;
+use winapi::um::libloaderapi::*;
 use winapi::um::wingdi::*;
 use winapi::um::winuser::*;
 
@@ -94,8 +96,25 @@ impl WglWrapper {
     }
 
     fn create() -> anyhow::Result<Self> {
-        let lib = libloading::Library::new("opengl32.dll")?;
-        log::trace!("loading opengl32.dll as {:?}", lib);
+        if is_swrast_preferred() {
+            let mesa_dir = std::env::current_exe()
+                .unwrap()
+                .parent()
+                .unwrap()
+                .join("mesa");
+            let mesa_dir = wide_string(mesa_dir.to_str().unwrap());
+
+            unsafe {
+                AddDllDirectory(mesa_dir.as_ptr());
+                SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
+            }
+        }
+
+        let lib = libloading::Library::new("opengl32.dll").map_err(|e| {
+            log::error!("{:?}", e);
+            e
+        })?;
+        log::trace!("loaded {:?}", lib);
 
         let get_proc_address: libloading::Symbol<GetProcAddressFunc> =
             unsafe { lib.get(b"wglGetProcAddress\0")? };