Expose non-widget rendering to embedders.

ports/libsimpleservo/api/src/lib.rs

@@ -63,10 +63,18 @@ pub struct InitOptions {
     pub xr_discovery: Option<webxr::Discovery>,
     pub gl_context_pointer: Option<*const c_void>,
     pub native_display_pointer: Option<*const c_void>,
-    pub native_widget: *mut c_void,
+    pub surfman_integration: SurfmanIntegration,
     pub prefs: Option<HashMap<String, PrefValue>>,
 }
 
+/// Controls how this embedding's rendering will integrate with the embedder.
+pub enum SurfmanIntegration {
+    /// Render directly to a provided native widget (see surfman::NativeWidget).
+    Widget(*mut c_void),
+    /// Render to an offscreen surface.
+    Surface,
+}
+
 #[derive(Clone, Debug)]
 pub struct Coordinates {
     pub viewport: Rect<i32, DevicePixel>,
@@ -253,13 +261,21 @@ pub fn init(
             .create_adapter()
             .or(Err("Failed to create adapter"))?,
     };
-    let native_widget = unsafe {
-        connection.create_native_widget_from_ptr(
-            init_opts.native_widget,
-            init_opts.coordinates.framebuffer.to_untyped(),
-        )
+    let surface_type = match init_opts.surfman_integration {
+        SurfmanIntegration::Widget(native_widget) => {
+            let native_widget = unsafe {
+                connection.create_native_widget_from_ptr(
+                    native_widget,
+                    init_opts.coordinates.framebuffer.to_untyped(),
+                )
+            };
+            SurfaceType::Widget { native_widget }
+        },
+        SurfmanIntegration::Surface => {
+            let size = init_opts.coordinates.framebuffer.to_untyped();
+            SurfaceType::Generic { size }
+        },
     };
-    let surface_type = SurfaceType::Widget { native_widget };
     let webrender_surfman = WebrenderSurfman::create(&connection, &adapter, surface_type)
         .or(Err("Failed to create surface manager"))?;
 

ports/libsimpleservo/capi/src/lib.rs

@@ -21,6 +21,7 @@ use simpleservo::{self, gl_glue, ServoGlue, SERVO};
 use simpleservo::{
     ContextMenuResult, Coordinates, DeviceIntRect, EventLoopWaker, HostTrait, InitOptions,
     InputMethodType, MediaSessionActionType, MediaSessionPlaybackState, MouseButton, PromptResult,
+    SurfmanIntegration,
 };
 use std::ffi::{CStr, CString};
 #[cfg(target_os = "windows")]
@@ -463,7 +464,7 @@ unsafe fn init(
         xr_discovery: None,
         gl_context_pointer: gl_context,
         native_display_pointer: display,
-        native_widget: opts.native_widget,
+        surfman_integration: SurfmanIntegration::Widget(opts.native_widget),
     };
 
     let wakeup = Box::new(WakeupCallback::new(wakeup));