external: avoid crashes on eglGetString() returning a nullptr.

doc/changelog.dox

@@ -496,6 +496,10 @@ See also:
     image converter plugin manager for cross-manager dependencies, broken since
     the removal of global shared manager state in 2020.06 (see
     [mosra/magnum#489](https://github.com/mosra/magnum/issues/489))
+-   Implementation of the @cpp "nv-egl-incorrect-gl11-function-pointers" @ce
+    @ref opengl-workarounds "OpenGL workaround" could lead to a crash if
+    @cpp eglQueryString() @ce would return a @cpp nullptr @ce (see
+    [mosra/magnum#535](https://github.com/mosra/magnum/issues/535))
 
 @subsection changelog-latest-deprecated Deprecated APIs
 

src/MagnumExternal/OpenGL/GL/flextGLPlatform.cpp

@@ -31,9 +31,9 @@
 #include "Magnum/Platform/Implementation/OpenGLFunctionLoader.h"
 
 #ifdef MAGNUM_PLATFORM_USE_EGL
-#include <cstring>
 #include <EGL/egl.h>
 #include <Corrade/Containers/StringView.h>
+
 #include "Magnum/GL/Context.h"
 #endif
 
@@ -48,8 +48,8 @@ void flextGLInit(Magnum::GL::Context& context) {
            linked GL 1.0 and 1.1 functions (such as glGetString()) and one has
            to retrieve them explicitly using eglGetProcAddress(). */
         EGLDisplay display = eglGetCurrentDisplay();
-        const char* vendor = eglQueryString(display, EGL_VENDOR);
+        const Corrade::Containers::StringView vendor = eglQueryString(display, EGL_VENDOR);
-        if(std::strcmp(vendor, "NVIDIA") == 0 && !context.isDriverWorkaroundDisabled("nv-egl-incorrect-gl11-function-pointers"_s)) {
+        if(vendor == "NVIDIA"_s && !context.isDriverWorkaroundDisabled("nv-egl-incorrect-gl11-function-pointers"_s)) {
 
             /* GL_VERSION_1_0 */
             flextGL.BlendFunc = reinterpret_cast<void(APIENTRY*)(GLenum, GLenum)>(loader.load("glBlendFunc"));

src/MagnumExternal/OpenGL/GL/flextGLPlatform.cpp.template

@@ -32,9 +32,9 @@
 #include "Magnum/Platform/Implementation/OpenGLFunctionLoader.h"
 
 #ifdef MAGNUM_PLATFORM_USE_EGL
-#include <cstring>
 #include <EGL/egl.h>
 #include <Corrade/Containers/StringView.h>
+
 #include "Magnum/GL/Context.h"
 #endif
 
@@ -49,8 +49,8 @@ void flextGLInit(Magnum::GL::Context& context) {
            linked GL 1.0 and 1.1 functions (such as glGetString()) and one has
            to retrieve them explicitly using eglGetProcAddress(). */
         EGLDisplay display = eglGetCurrentDisplay();
-        const char* vendor = eglQueryString(display, EGL_VENDOR);
+        const Corrade::Containers::StringView vendor = eglQueryString(display, EGL_VENDOR);
-        if(std::strcmp(vendor, "NVIDIA") == 0 && !context.isDriverWorkaroundDisabled("nv-egl-incorrect-gl11-function-pointers"_s)) {
+        if(vendor == "NVIDIA"_s && !context.isDriverWorkaroundDisabled("nv-egl-incorrect-gl11-function-pointers"_s)) {
             @for category,funcs in functions:
             @if funcs and category in ['VERSION_1_0', 'VERSION_1_1']: