From 6b3786457f5881a752de04150f964de7d4c0398d Mon Sep 17 00:00:00 2001
From: Stephen Just <stephenjust@gmail.com>
Date: Tue, 19 Aug 2014 16:08:27 -0600
Subject: [PATCH] Fix OpenGL extension detection on Linux/Mesa.

Created function in glwrap to test whether a GL extension is available.
This required using OpenGL3's glGetStringi. Backwards compat code can
be added to function if necessary.
---
 src/graphics/glwrap.cpp     | 16 ++++++++++++++++
 src/graphics/glwrap.hpp     |  3 +++
 src/graphics/irr_driver.cpp |  6 +++---
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/graphics/glwrap.cpp b/src/graphics/glwrap.cpp
index 6cddac011..13da4236b 100644
--- a/src/graphics/glwrap.cpp
+++ b/src/graphics/glwrap.cpp
@@ -1213,3 +1213,19 @@ void GL32_draw2DRectangle(video::SColor color, const core::rect<s32>& position,
 
     glGetError();
 }
+
+bool hasGLExtension(const char* extension) {
+    GLint numExtensions = 0;
+    glGetIntegerv(GL_NUM_EXTENSIONS, &numExtensions);
+    Log::debug("GLWrap", "Found %d OpenGL Extensions", numExtensions);
+    for (GLint i = 0; i < numExtensions; i++) {
+        const char* foundExtension =
+            (const char*) glGetStringi(GL_EXTENSIONS, i);
+        if (foundExtension && strcmp(foundExtension, extension) == 0) {
+            Log::debug("GLWrap", "Extension %s found", extension);
+            return true;
+        }
+    }
+    Log::debug("GLWrap", "Extension %s not found", extension);
+    return false;
+}
diff --git a/src/graphics/glwrap.hpp b/src/graphics/glwrap.hpp
index dea33ae85..20d0f425d 100644
--- a/src/graphics/glwrap.hpp
+++ b/src/graphics/glwrap.hpp
@@ -162,4 +162,7 @@ void draw2DImage(const irr::video::ITexture* texture, const irr::core::rect<s32>
 
 void GL32_draw2DRectangle(irr::video::SColor color, const irr::core::rect<s32>& position,
     const irr::core::rect<s32>* clip = 0);
+
+bool hasGLExtension(const char* extension);
+
 #endif
diff --git a/src/graphics/irr_driver.cpp b/src/graphics/irr_driver.cpp
index 5bcf11334..2ccf581d2 100644
--- a/src/graphics/irr_driver.cpp
+++ b/src/graphics/irr_driver.cpp
@@ -486,9 +486,9 @@ void IrrDriver::initDevice()
     // Default false value for hasVSLayer if --no-graphics argument is used
     if (!ProfileWorld::isNoGraphics())
     {
-        const GLubyte *extensions = glGetString(GL_EXTENSIONS);
-        if (extensions && strstr((const char*)extensions, "GL_AMD_vertex_shader_layer") != NULL)
-        hasVSLayer = true;
+        if (hasGLExtension("GL_AMD_vertex_shader_layer")) {
+            hasVSLayer = true;
+        }
     }