feat(gpu): refine backend choices, Metal labels, and graphics options per platform

src/gpu_backend.rs

@@ -96,9 +96,12 @@ impl BackendChoice {
         let mut v = vec![BackendChoice::Auto];
         if cfg!(target_os = "windows") {
             v.push(BackendChoice::Dx12);
+            v.push(BackendChoice::Vulkan);
+            v.push(BackendChoice::Gl);
+        } else if cfg!(target_os = "linux") {
+            v.push(BackendChoice::Vulkan);
+            v.push(BackendChoice::Gl);
         }
-        v.push(BackendChoice::Vulkan);
-        v.push(BackendChoice::Gl);
         v
     }
 
@@ -123,7 +126,13 @@ impl BackendChoice {
 
     pub fn label(self) -> &'static str {
         match self {
-            BackendChoice::Auto => "Automatic (recommended)",
+            BackendChoice::Auto => {
+                if cfg!(target_os = "macos") {
+                    "Automatic (Metal)"
+                } else {
+                    "Automatic (recommended)"
+                }
+            }
             BackendChoice::Dx12 => "DirectX 12",
             BackendChoice::Vulkan => "Vulkan",
             BackendChoice::Gl => "OpenGL",
@@ -236,7 +245,13 @@ pub fn active_gpu_summary() -> String {
         Some("gl") => "OpenGL",
         Some("metal") => "Metal",
         Some(other) => other,
-        None => "default",
+        None => {
+            if cfg!(target_os = "macos") {
+                "Metal"
+            } else {
+                "default"
+            }
+        }
     };
     match a.adapter {
         Some(name) => format!("{name} ({backend})"),
@@ -1536,6 +1551,34 @@ mod tests {
         assert_eq!(BackendChoice::parse("garbage"), BackendChoice::Auto);
     }
 
+    #[test]
+    fn backend_choices_match_target_os() {
+        let choices = BackendChoice::available();
+        assert!(choices.contains(&BackendChoice::Auto));
+        if cfg!(target_os = "windows") {
+            assert_eq!(
+                choices,
+                vec![
+                    BackendChoice::Auto,
+                    BackendChoice::Dx12,
+                    BackendChoice::Vulkan,
+                    BackendChoice::Gl,
+                ]
+            );
+        } else if cfg!(target_os = "linux") {
+            assert_eq!(
+                choices,
+                vec![
+                    BackendChoice::Auto,
+                    BackendChoice::Vulkan,
+                    BackendChoice::Gl,
+                ]
+            );
+        } else if cfg!(target_os = "macos") {
+            assert_eq!(choices, vec![BackendChoice::Auto]);
+        }
+    }
+
     #[test]
     fn graphics_prefs_persist_and_default_when_missing() {
         let _guard = SENTINEL_TESTS.lock().unwrap_or_else(|e| e.into_inner());

src/ui/window/about.rs

@@ -152,6 +152,10 @@ pub(crate) fn report() -> String {
             prefs.legacy_gl,
         ));
     }
+    #[cfg(target_arch = "wasm32")]
+    {
+        out.push_str("\n[Graphics]\nBackend: WebGPU / WebGL\n");
+    }
     out
 }
 

src/ui/window/options/graphics.rs

@@ -35,7 +35,7 @@ pub(crate) fn view(prefs: GraphicsPrefs, active: ActiveGpu) -> Element<'static,
     .on_select(Message::GraphicsBackendChanged)
     .width(260);
 
-    column![
+    let mut col = column![
         text(crate::t!("Graphics")).size(15),
         Space::new().height(6),
         text(crate::t!(
@@ -55,7 +55,20 @@ pub(crate) fn view(prefs: GraphicsPrefs, active: ActiveGpu) -> Element<'static,
         Space::new().height(4),
         current_row(
             crate::t!("Backend"),
-            unknown(active.backend.as_deref().unwrap_or(""))
+            match active.backend.as_deref() {
+                Some("dx12") => "DirectX 12".to_string(),
+                Some("vulkan") => "Vulkan".to_string(),
+                Some("gl") => "OpenGL".to_string(),
+                Some("metal") => "Metal".to_string(),
+                Some(other) => other.to_string(),
+                None => {
+                    if cfg!(target_os = "macos") {
+                        "Metal".to_string()
+                    } else {
+                        unknown("")
+                    }
+                }
+            },
         ),
         Space::new().height(4),
         current_row(crate::t!("Selected by"), unknown(&active.origin)),
@@ -77,26 +90,33 @@ pub(crate) fn view(prefs: GraphicsPrefs, active: ActiveGpu) -> Element<'static,
         ]
         .spacing(8)
         .align_y(iced::Center),
-        Space::new().height(10),
+    ];
-        row![
+
-            checkbox(prefs.legacy_gl)
+    if cfg!(target_os = "windows") {
-                .on_toggle(Message::GraphicsLegacyGlToggled)
+        col = col.push(Space::new().height(10)).push(
-                .size(15),
+            row![
+                checkbox(prefs.legacy_gl)
+                    .on_toggle(Message::GraphicsLegacyGlToggled)
+                    .size(15),
+                text(crate::t!(
+                    "Prefer OpenGL on older GPUs (automatic backend only)"
+                ))
+                .size(12),
+            ]
+            .spacing(8)
+            .align_y(iced::Center),
+        );
+    }
+
+    col.push(Space::new().height(16))
+        .push(
             text(crate::t!(
-                "Prefer OpenGL on older GPUs (Windows, automatic backend only)"
+                "If a pinned backend fails to start, the next launch falls back to automatic selection. \
+                 The --backend option and the WGPU_BACKEND variable override this page."
             ))
-            .size(12),
+            .size(11)
-        ]
+            .width(Fill),
-        .spacing(8)
+        )
-        .align_y(iced::Center),
+        .spacing(0)
-        Space::new().height(16),
+        .into()
-        text(crate::t!(
-            "If a pinned backend fails to start, the next launch falls back to automatic selection. \
-             The --backend option and the WGPU_BACKEND variable override this page."
-        ))
-        .size(11)
-        .width(Fill),
-    ]
-    .spacing(0)
-    .into()
 }