Examples: SDL2+OpenGL3: Provide ES3 context creation code + failure h…

…andling. (#8197)

examples/example_sdl2_opengl3/main.cpp

@@ -35,12 +35,19 @@ int main(int, char**)
 
     // Decide GL+GLSL versions
 #if defined(IMGUI_IMPL_OPENGL_ES2)
-    // GL ES 2.0 + GLSL 100
+    // GL ES 2.0 + GLSL 100 (WebGL 1.0)
     const char* glsl_version = "#version 100";
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+#elif defined(IMGUI_IMPL_OPENGL_ES3)
+    // GL ES 3.0 + GLSL 300 es (WebGL 2.0)
+    const char* glsl_version = "#version 300 es";
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
 #elif defined(__APPLE__)
     // GL 3.2 Core + GLSL 150
     const char* glsl_version = "#version 150";
@@ -75,6 +82,12 @@ int main(int, char**)
     }
 
     SDL_GLContext gl_context = SDL_GL_CreateContext(window);
+    if (gl_context == nullptr)
+    {
+        printf("Error: SDL_GL_CreateContext(): %s\n", SDL_GetError());
+        return -1;
+    }
+
     SDL_GL_MakeCurrent(window, gl_context);
     SDL_GL_SetSwapInterval(1); // Enable vsync