From 1fe22e24d020d9d933a4ed7bfd618e634830023c Mon Sep 17 00:00:00 2001
From: binary1248 <binary1248@hotmail.com>
Date: Mon, 19 May 2014 08:42:42 +0200
Subject: [PATCH] Fix the case where not having created a GlResource prior to
 calling Shader::isAvailable() would break context management. (#211)

---
 src/SFML/Graphics/Shader.cpp | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/SFML/Graphics/Shader.cpp b/src/SFML/Graphics/Shader.cpp
index 805b6b6f..0b3f1751 100644
--- a/src/SFML/Graphics/Shader.cpp
+++ b/src/SFML/Graphics/Shader.cpp
@@ -29,6 +29,7 @@
 #include <SFML/Graphics/Shader.hpp>
 #include <SFML/Graphics/Texture.hpp>
 #include <SFML/Graphics/GLCheck.hpp>
+#include <SFML/Window/Context.hpp>
 #include <SFML/System/InputStream.hpp>
 #include <SFML/System/Err.hpp>
 #include <fstream>
@@ -437,15 +438,29 @@ void Shader::bind(const Shader* shader)
 ////////////////////////////////////////////////////////////
 bool Shader::isAvailable()
 {
-    ensureGlContext();
+    static bool available = false;
+    static bool checked = false;
 
-    // Make sure that extensions are initialized
-    priv::ensureExtensionsInit();
+    // Make sure we only have to check once
+    if (!checked)
+    {
+        // Create a temporary context in case the user checks
+        // before a GlResource is created, thus initializing
+        // the shared context
+        Context context;
 
-    return GLEW_ARB_shading_language_100 &&
-           GLEW_ARB_shader_objects       &&
-           GLEW_ARB_vertex_shader        &&
-           GLEW_ARB_fragment_shader;
+        // Make sure that extensions are initialized
+        priv::ensureExtensionsInit();
+
+        available = GLEW_ARB_shading_language_100 &&
+                    GLEW_ARB_shader_objects       &&
+                    GLEW_ARB_vertex_shader        &&
+                    GLEW_ARB_fragment_shader;
+
+        checked = true;
+    }
+
+    return available;
 }