glx: Support making a context current without surface

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Add `PossiblyCurrentContext::make_not_current_in_place(&self)` for when `Send` capability of `NotCurrentContext` is not required.
 - Add `NotCurrentContext::make_current_surfaceless(self)` and `PossiblyCurrentContext::make_current_surfaceless(&self)` in the `Cgl` implementation to allow the use of surfaceless contexts on MacOS.
+- Add `NotCurrentContext::make_current_surfaceless(self)` and `PossiblyCurrentContext::make_current_surfaceless(&self)` in the `Glx` implementation to allow the use of surfaceless contexts with GLX.
 
 # Version 0.32.1
 

glutin/src/api/glx/context.rs

@@ -41,13 +41,14 @@ impl Display {
             std::ptr::null()
         };
 
-        let context = if self.inner.client_extensions.contains("GLX_ARB_create_context")
-            && self.inner.glx_extra.is_some()
-        {
-            self.create_context_arb(config, context_attributes, shared_context)?
-        } else {
-            self.create_context_legacy(config, shared_context)?
-        };
+        let (context, supports_surfaceless) =
+            if self.inner.client_extensions.contains("GLX_ARB_create_context")
+                && self.inner.glx_extra.is_some()
+            {
+                self.create_context_arb(config, context_attributes, shared_context)?
+            } else {
+                (self.create_context_legacy(config, shared_context)?, false)
+            };
 
         // Failed to create the context.
         if context.is_null() {
@@ -56,8 +57,13 @@ impl Display {
 
         let config = config.clone();
         let is_gles = matches!(context_attributes.api, Some(ContextApi::Gles(_)));
-        let inner =
-            ContextInner { display: self.clone(), config, raw: GlxContext(context), is_gles };
+        let inner = ContextInner {
+            display: self.clone(),
+            config,
+            raw: GlxContext(context),
+            is_gles,
+            supports_surfaceless,
+        };
 
         Ok(NotCurrentContext::new(inner))
     }
@@ -67,14 +73,14 @@ impl Display {
         config: &Config,
         context_attributes: &ContextAttributes,
         shared_context: GLXContext,
-    ) -> Result<GLXContext> {
+    ) -> Result<(GLXContext, bool)> {
         let extra = self.inner.glx_extra.as_ref().unwrap();
         let mut attrs = Vec::<c_int>::with_capacity(16);
 
         // Check whether the ES context creation is supported.
         let supports_es = self.inner.features.contains(DisplayFeatures::CREATE_ES_CONTEXT);
 
-        let (profile, version) = match context_attributes.api {
+        let (profile, version, supports_surfaceless) = match context_attributes.api {
             api @ Some(ContextApi::OpenGl(_)) | api @ None => {
                 let version = api.and_then(|api| api.version());
                 let (profile, version) = context::pick_profile(context_attributes.profile, version);
@@ -83,11 +89,16 @@ impl Display {
                     GlProfile::Compatibility => glx_extra::CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB,
                 };
 
-                (Some(profile), Some(version))
+                // Surfaceless contexts are supported with the GLX_ARB_create_context extension
+                // when using OpenGL 3.0 or greater.
+                let supports_surfaceless = version >= Version::new(3, 0);
+
+                (Some(profile), Some(version), supports_surfaceless)
             },
             Some(ContextApi::Gles(version)) if supports_es => (
                 Some(glx_extra::CONTEXT_ES2_PROFILE_BIT_EXT),
                 Some(version.unwrap_or(Version::new(2, 0))),
+                false,
             ),
             _ => {
                 return Err(ErrorKind::NotSupported(
@@ -188,7 +199,7 @@ impl Display {
         // Terminate list with zero.
         attrs.push(0);
 
-        super::last_glx_error(|| unsafe {
+        let context = super::last_glx_error(|| unsafe {
             extra.CreateContextAttribsARB(
                 self.inner.raw.cast(),
                 *config.inner.raw,
@@ -197,7 +208,9 @@ impl Display {
                 1,
                 attrs.as_ptr(),
             )
-        })
+        })?;
+
+        Ok((context, supports_surfaceless))
     }
 
     fn create_context_legacy(
@@ -228,6 +241,15 @@ pub struct NotCurrentContext {
 }
 
 impl NotCurrentContext {
+    /// Make a [`Self::PossiblyCurrentContext`] indicating that the context
+    /// could be current on the thread.
+    ///
+    /// Requires the GLX_ARB_create_context extension and OpenGL 3.0 or greater.
+    pub fn make_current_surfaceless(self) -> Result<PossiblyCurrentContext> {
+        self.inner.make_current_surfaceless()?;
+        Ok(PossiblyCurrentContext { inner: self.inner, _nosendsync: PhantomData })
+    }
+
     fn new(inner: ContextInner) -> Self {
         Self { inner }
     }
@@ -297,6 +319,15 @@ pub struct PossiblyCurrentContext {
     _nosendsync: PhantomData<GLXContext>,
 }
 
+impl PossiblyCurrentContext {
+    /// Make this context current on the calling thread.
+    ///
+    /// Requires the GLX_ARB_create_context extension and OpenGL 3.0 or greater.
+    pub fn make_current_surfaceless(&self) -> Result<()> {
+        self.inner.make_current_surfaceless()
+    }
+}
+
 impl PossiblyCurrentGlContext for PossiblyCurrentContext {
     type NotCurrentContext = NotCurrentContext;
     type Surface<T: SurfaceTypeTrait> = Surface<T>;
@@ -362,9 +393,29 @@ struct ContextInner {
     config: Config,
     raw: GlxContext,
     is_gles: bool,
+    supports_surfaceless: bool,
 }
 
 impl ContextInner {
+    fn make_current_surfaceless(&self) -> Result<()> {
+        if !self.supports_surfaceless {
+            return Err(
+                ErrorKind::NotSupported("the surfaceless context Api isn't supported").into()
+            );
+        }
+
+        // Passing zero arguments for both `draw` and `read` parameters makes
+        // the context current without a default framebuffer.
+        super::last_glx_error(|| unsafe {
+            self.display.inner.glx.MakeContextCurrent(
+                self.display.inner.raw.cast(),
+                0,
+                0,
+                *self.raw,
+            );
+        })
+    }
+
     fn make_current_draw_read<T: SurfaceTypeTrait>(
         &self,
         surface_draw: &Surface<T>,