From a91c68601f390999a5691b17fc452521ddd691f9 Mon Sep 17 00:00:00 2001
From: aspioupiou <stephane@sbtech.fr>
Date: Thu, 30 Apr 2020 13:04:22 +0200
Subject: [PATCH] EGLDisplay non-terminating when mixing
 WindowlessEGLApplication & shared contexts

---
 .../Platform/WindowlessEglApplication.cpp      | 18 ++++++++++++++++--
 src/Magnum/Platform/WindowlessEglApplication.h |  3 +++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/Magnum/Platform/WindowlessEglApplication.cpp b/src/Magnum/Platform/WindowlessEglApplication.cpp
index 1d156633f..27c3f6442 100644
--- a/src/Magnum/Platform/WindowlessEglApplication.cpp
+++ b/src/Magnum/Platform/WindowlessEglApplication.cpp
@@ -83,6 +83,8 @@ bool extensionSupported(const char* const extensions, Containers::ArrayView<cons
 
 WindowlessEglContext::WindowlessEglContext(const Configuration& configuration, GLContext* const magnumContext) {
     #ifndef MAGNUM_TARGET_WEBGL
+    
+     
     /* If relevant extensions are supported, try to find some display using
        those APIs, as that works reliably also when running headless. This
        would ideally use EGL 1.5 APIs but since we still want to support
@@ -272,7 +274,9 @@ WindowlessEglContext::WindowlessEglContext(const Configuration& configuration, G
         contextFlags = EGL_NONE;
     }
     #endif
-
+    
+    if(configuration.sharedContext() != EGL_NO_CONTEXT) _sharedContext = true; 
+    
     if(!(_context = eglCreateContext(_display, config,
         #ifndef MAGNUM_TARGET_WEBGL
         configuration.sharedContext(),
@@ -309,7 +313,17 @@ WindowlessEglContext::~WindowlessEglContext() {
     #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)
     if(_surface) eglDestroySurface(_display, _surface);
     #endif
-    if(_display) eglTerminate(_display);
+    
+    /**
+     * From Khronos, `Multiple calls made to eglGetPlatformDisplayEXT with the same <platform> 
+     * and <native_display> will return the same EGLDisplay handle.` This makes a problem when 
+     * the context is shared with another one, because both shares the same EGLDisplay.
+     * To avoid errors when trying to make current the other context (EGL_NOT_INITIALIZED) 
+     * we don't terminate the shared display.
+     * It is then the user's responsaibility to first kill the shared EGL instance 
+     * (which won't terminate the display), and then main one, killing everything.
+     */
+    if(_sharedContext && _display) eglTerminate(_display);
 }
 
 WindowlessEglContext& WindowlessEglContext::operator=(WindowlessEglContext && other) {
diff --git a/src/Magnum/Platform/WindowlessEglApplication.h b/src/Magnum/Platform/WindowlessEglApplication.h
index bc023f85b..f7566d452 100644
--- a/src/Magnum/Platform/WindowlessEglApplication.h
+++ b/src/Magnum/Platform/WindowlessEglApplication.h
@@ -132,6 +132,9 @@ class WindowlessEglContext {
         EGLContext glContext() { return _context; }
 
     private:
+        /* Stores whether the EGL context is shared or not */
+    	bool _sharedContext = false;
+    	
         EGLDisplay _display{};
         EGLContext _context{};
         #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_WEBGL)