feat(desktop): add GPU selection policy (#1442)

Co-authored-by: Michael Aaron Murphy <michael@mmurphy.dev>

src/desktop.rs

@@ -1,6 +1,8 @@
 #[cfg(not(windows))]
 pub use freedesktop_desktop_entry as fde;
 #[cfg(not(windows))]
+pub mod gpu;
+#[cfg(not(windows))]
 pub use mime::Mime;
 use std::path::{Path, PathBuf};
 #[cfg(not(windows))]

src/desktop/gpu.rs

@@ -0,0 +1,56 @@
+// Copyright 2026 System76 <info@system76.com>
+// SPDX-License-Identifier: MPL-2.0
+
+use std::collections::HashMap;
+
+/// An available GPU that can be selected by a launcher.
+#[derive(Debug, Clone)]
+pub struct Descriptor {
+    pub name: String,
+    pub environment: HashMap<String, String>,
+    pub default: bool,
+    pub discrete: bool,
+}
+
+/// A preference to use when choosing a GPU to launch with.
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
+pub enum Preference {
+    #[default]
+    Default,
+    NonDefault,
+}
+
+impl Preference {
+    /// Find the preferred default GPU for this preference.
+    pub fn preferred(self, gpus: &[Descriptor]) -> Option<usize> {
+        let default_idx = gpus.iter().position(|gpu| gpu.default);
+        if matches!(self, Preference::Default) {
+            return default_idx;
+        }
+
+        let default_discrete = gpus.iter().position(|gpu| gpu.default && gpu.discrete);
+        if default_discrete.is_some() {
+            return default_discrete;
+        }
+
+        let non_default_discrete = gpus.iter().position(|gpu| gpu.discrete);
+        let non_default = || gpus.iter().position(|gpu| !gpu.default);
+        non_default_discrete.or_else(non_default).or(default_idx)
+    }
+
+    /// Select the GPU override to launch with.
+    pub fn select(self, gpus: &[Descriptor]) -> Option<usize> {
+        if matches!(self, Preference::Default) {
+            return None;
+        }
+
+        let default_discrete = gpus.iter().position(|gpu| gpu.default && gpu.discrete);
+        if default_discrete.is_some() {
+            return None;
+        }
+
+        let non_default_discrete = gpus.iter().position(|gpu| gpu.discrete);
+        let non_default = || gpus.iter().position(|gpu| !gpu.default);
+        non_default_discrete.or_else(non_default)
+    }
+}