egl: Fallback if EGL_KHR_display_reference not supported

libglvnd reports client extensions if at least one vendor supports them.
This might lead to display creation failure when a vendor library reports support but
fails to create a display for another reason (like when the nvidia egl implementation is installed but no nvidia card is available).
To work around this issue retry creation without EGL_KHR_display_reference.

glutin/src/api/egl/display.rs

@@ -127,15 +127,17 @@ impl Display {
 
         let mut attrs = Vec::<EGLint>::with_capacity(3);
 
-        if extensions.contains("EGL_KHR_display_reference") {
-            attrs.push(egl::TRACK_REFERENCES_KHR as _);
-            attrs.push(egl::TRUE as _);
-        }
-
         // TODO: Some extensions exist like EGL_EXT_device_drm which allow specifying
         // which DRM master fd to use under the hood by the implementation. This would
         // mean there would need to be an unsafe equivalent to this function.
 
+        // Push at the end so we can pop it on failure
+        let has_display_reference = extensions.contains("EGL_KHR_display_reference");
+        if has_display_reference {
+            attrs.push(egl::TRACK_REFERENCES_KHR as _);
+            attrs.push(egl::TRUE as _);
+        }
+
         // Push `egl::NONE` to terminate the list.
         attrs.push(egl::NONE as EGLint);
 
@@ -146,6 +148,23 @@ impl Display {
                 attrs.as_ptr(),
             )
         })
+        .or_else(|err| {
+            if has_display_reference {
+                attrs.pop();
+                attrs.pop();
+                attrs.pop();
+                attrs.push(egl::NONE as EGLint);
+                Self::check_display_error(unsafe {
+                    egl.GetPlatformDisplayEXT(
+                        egl::PLATFORM_DEVICE_EXT,
+                        device.raw_device() as *mut _,
+                        attrs.as_ptr(),
+                    )
+                })
+            } else {
+                Err(err)
+            }
+        })
         .map(EglDisplay::Ext)?;
 
         Self::initialize_display(egl, display, None)
@@ -244,23 +263,40 @@ impl Display {
             },
         };
 
-        if extensions.contains("EGL_KHR_display_reference") {
-            attrs.push(egl::TRACK_REFERENCES_KHR as _);
-            attrs.push(egl::TRUE as _);
-        }
-
         // Be explicit here.
         if display.is_null() {
             display = egl::DEFAULT_DISPLAY as *mut _;
         }
 
+        // Push at the end so we can pop it on failure
+        let has_display_reference = extensions.contains("EGL_KHR_display_reference");
+        if has_display_reference {
+            attrs.push(egl::TRACK_REFERENCES_KHR as _);
+            attrs.push(egl::TRUE as _);
+        }
+
         // Push `egl::NONE` to terminate the list.
         attrs.push(egl::NONE as EGLAttrib);
 
-        let display =
+        let platform_display =
             unsafe { egl.GetPlatformDisplay(platform, display as *mut _, attrs.as_ptr()) };
 
-        Self::check_display_error(display).map(EglDisplay::Khr)
+        Self::check_display_error(platform_display)
+            .or_else(|err| {
+                if has_display_reference {
+                    attrs.pop();
+                    attrs.pop();
+                    attrs.pop();
+                    attrs.push(egl::NONE as EGLAttrib);
+                    let platform_display = unsafe {
+                        egl.GetPlatformDisplay(platform, display as *mut _, attrs.as_ptr())
+                    };
+                    Self::check_display_error(platform_display)
+                } else {
+                    Err(err)
+                }
+            })
+            .map(EglDisplay::Khr)
     }
 
     fn get_platform_display_ext(egl: &Egl, display: RawDisplayHandle) -> Result<EglDisplay> {
@@ -309,33 +345,50 @@ impl Display {
             },
         };
 
-        if extensions.contains("EGL_KHR_display_reference") {
-            attrs.push(egl::TRACK_REFERENCES_KHR as _);
-            attrs.push(egl::TRUE as _);
-        }
-
         // Be explicit here.
         if display.is_null() {
             display = egl::DEFAULT_DISPLAY as *mut _;
         }
 
+        // Push at the end so we can pop it on failure
+        let has_display_reference = extensions.contains("EGL_KHR_display_reference");
+        if has_display_reference {
+            attrs.push(egl::TRACK_REFERENCES_KHR as _);
+            attrs.push(egl::TRUE as _);
+        }
+
         // Push `egl::NONE` to terminate the list.
         attrs.push(egl::NONE as EGLint);
 
-        let display =
+        let platform_display =
             unsafe { egl.GetPlatformDisplayEXT(platform, display as *mut _, attrs.as_ptr()) };
 
-        Self::check_display_error(display).map(|display| {
-            if legacy {
-                // NOTE: For angle we use the Legacy code path, as that uses CreateWindowSurface
-                // instead of CreatePlatformWindowSurface*. The latter somehow
-                // doesn't work, only the former does. But Angle's own example also use the
-                // former: https://github.com/google/angle/blob/main/util/EGLWindow.cpp#L424
-                EglDisplay::Legacy(display)
-            } else {
-                EglDisplay::Ext(display)
-            }
-        })
+        Self::check_display_error(platform_display)
+            .or_else(|err| {
+                if has_display_reference {
+                    attrs.pop();
+                    attrs.pop();
+                    attrs.pop();
+                    attrs.push(egl::NONE as EGLint);
+                    let platform_display = unsafe {
+                        egl.GetPlatformDisplayEXT(platform, display as *mut _, attrs.as_ptr())
+                    };
+                    Self::check_display_error(platform_display)
+                } else {
+                    Err(err)
+                }
+            })
+            .map(|display| {
+                if legacy {
+                    // NOTE: For angle we use the Legacy code path, as that uses CreateWindowSurface
+                    // instead of CreatePlatformWindowSurface*. The latter somehow
+                    // doesn't work, only the former does. But Angle's own example also use the
+                    // former: https://github.com/google/angle/blob/main/util/EGLWindow.cpp#L424
+                    EglDisplay::Legacy(display)
+                } else {
+                    EglDisplay::Ext(display)
+                }
+            })
     }
 
     fn get_display(egl: &Egl, display: RawDisplayHandle) -> Result<EglDisplay> {