From a2e47d2d0ec069bd0a0b115c984278331de98071 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 21 Mar 2019 09:46:46 +0530
Subject: [PATCH] EGL: Warn if non-blocking swap buffers is not available

---
 glfw/egl_context.c | 10 +++++++++-
 glfw/egl_context.h |  2 ++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/glfw/egl_context.c b/glfw/egl_context.c
index b2d11a471..604582c1b 100644
--- a/glfw/egl_context.c
+++ b/glfw/egl_context.c
@@ -612,6 +612,15 @@ GLFWbool _glfwCreateContextEGL(_GLFWwindow* window,
 
     window->context.egl.config = config;
 
+    EGLint a = EGL_MIN_SWAP_INTERVAL;
+    if (!eglGetConfigAttrib(_glfw.egl.display, config, a, &a)) {
+        _glfwInputError(GLFW_VERSION_UNAVAILABLE, "EGL: could not check for non-blocking buffer swap with error: %s", getEGLErrorString(eglGetError()));
+    } else {
+        if (a > 0) {
+            _glfwInputError(GLFW_VERSION_UNAVAILABLE, "EGL: non-blocking swap buffers not available, minimum swap interval is: %d", a);
+        }
+    }
+
     // Load the appropriate client library
     if (!_glfw.egl.KHR_get_all_proc_addresses)
     {
@@ -783,4 +792,3 @@ GLFWAPI EGLSurface glfwGetEGLSurface(GLFWwindow* handle)
 
     return window->context.egl.surface;
 }
-
diff --git a/glfw/egl_context.h b/glfw/egl_context.h
index 633d98485..534beb8c8 100644
--- a/glfw/egl_context.h
+++ b/glfw/egl_context.h
@@ -87,6 +87,8 @@ typedef struct wl_egl_window* EGLNativeWindowType;
 #define EGL_NO_DISPLAY ((EGLDisplay) 0)
 #define EGL_NO_CONTEXT ((EGLContext) 0)
 #define EGL_DEFAULT_DISPLAY ((EGLNativeDisplayType) 0)
+#define EGL_MIN_SWAP_INTERVAL             0x303B
+#define EGL_MAX_SWAP_INTERVAL             0x303C
 
 #define EGL_CONTEXT_OPENGL_FORWARD_COMPATIBLE_BIT_KHR 0x00000002
 #define EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT_KHR 0x00000001