GLContextGLX: try all GL versions from the highest.

ui/gl/gl_context_glx.cc

Index: ui/gl/gl_context_glx.cc
diff --git a/ui/gl/gl_context_glx.cc b/ui/gl/gl_context_glx.cc
index aee3fedeab5a040d8ff9373200787657c485bb8a..220af7ae9ef59920ddaa8a3d3245c672669247c5 100644
--- a/ui/gl/gl_context_glx.cc
+++ b/ui/gl/gl_context_glx.cc
@@ -19,6 +19,134 @@ extern "C" {
 
 namespace gfx {
 
+namespace {
+
+static int IgnoreX11Errors(Display*, XErrorEvent*) {
+  return 0;
+}
+
+using GLVersion = std::pair<int, int>;
+
+GLXContext CreateContextAttribs(Display* display,
+                                GLXFBConfig config,
+                                GLXContext share,
+                                GLVersion version,
+                                int profileMask) {
+  std::vector<int> attribs;
+
+  if (GLSurfaceGLX::IsCreateContextRobustnessSupported()) {
+    attribs.push_back(GLX_CONTEXT_RESET_NOTIFICATION_STRATEGY_ARB);
+    attribs.push_back(GLX_LOSE_CONTEXT_ON_RESET_ARB);
+  }
+
+  if (version.first == 0 && version.second == 0) {
+    attribs.push_back(GLX_CONTEXT_MAJOR_VERSION_ARB);
+    attribs.push_back(version.first);
+
+    attribs.push_back(GLX_CONTEXT_MINOR_VERSION_ARB);
+    attribs.push_back(version.second);
+  }
+
+  if (profileMask != 0 && GLSurfaceGLX::IsCreateContextProfileSupported()) {
+    attribs.push_back(GLX_CONTEXT_PROFILE_MASK_ARB);
+    attribs.push_back(profileMask);
+  }
+
+  attribs.push_back(0);
+
+  // When creating a context with glXCreateContextAttribsARB, a variety of X11
+  // errors can be generated. To prevent these errors from crashing our process,
+  // we simply ignore them and only look if the GLXContext was created.
+  auto oldErrorHandler = XSetErrorHandler(IgnoreX11Errors);
+  GLXContext context =
+      glXCreateContextAttribsARB(display, config, share, True, attribs.data());
+  XSetErrorHandler(oldErrorHandler);
+
+  return context;
+}
+
+GLXContext CreateHighestVersionContext(Display* display,
+                                       GLXFBConfig config,
+                                       GLXContext share) {
+  // It is commonly assumed that glXCreateContextAttrib will create a context
+  // of the highest version possible but it is not specified in the spec and
+  // is not true on the Mesa drivers. On Mesa, Instead we try to create a
+  // context per GL version until we succeed, starting from newer version.
+  // On both Mesa and other drivers we try to create a desktop context and fall
+  // back to ES context.
+  // The code could be simpler if the Mesa code path was used for all drivers,
+  // however the cost of failing a context creation can be high (3 milliseconds
+  // for the NVIDIA driver). The good thing is that failed context creation only
+  // takes 0.1 milliseconds on Mesa.
+
+  struct ContextCreationInfo {
+    int profileFlag;
+    GLVersion version;
+  };
+
+  // clang-format off
+  // For regular drivers we try to create a core, compatibility, then ES
+  // context. Without requiring any specific version.
+  const ContextCreationInfo contextsToTry[] = {

[piman, 2016/05/25 22:35:17]

nit: chrome style
contexts_to_try

+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, GLVersion(0, 0) },
+      { 0, GLVersion(0, 0) },
+      { GLX_CONTEXT_ES2_PROFILE_BIT_EXT, GLVersion(0, 0) },
+  };
+
+  // On Mesa we try to create a core context, except for versions below 3.2
+  // where it is not applicable. (and fallback to ES as well)
+  const ContextCreationInfo mesaContextsToTry[] = {

[piman, 2016/05/25 22:35:17]

nit: mesa_contexts_to_try

+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 5) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 4) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 3) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 2) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 1) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(4, 0) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(3, 3) } },
+      { GLX_CONTEXT_CORE_PROFILE_BIT_ARB, { GLVersion(3, 2) } },
+      { 0, { GLVersion(3, 1) } },
+      { 0, { GLVersion(3, 0) } },
+      { 0, { GLVersion(2, 0) } },
+      { 0, { GLVersion(1, 5) } },
+      { 0, { GLVersion(1, 4) } },
+      { 0, { GLVersion(1, 3) } },
+      { 0, { GLVersion(1, 2) } },
+      { 0, { GLVersion(1, 1) } },
+      { 0, { GLVersion(1, 0) } },
+      { GLX_CONTEXT_ES2_PROFILE_BIT_EXT, { GLVersion(3, 2) } },
+      { GLX_CONTEXT_ES2_PROFILE_BIT_EXT, { GLVersion(3, 1) } },
+      { GLX_CONTEXT_ES2_PROFILE_BIT_EXT, { GLVersion(3, 0) } },
+      { GLX_CONTEXT_ES2_PROFILE_BIT_EXT, { GLVersion(2, 0) } },
+  };
+  // clang-format on
+
+  std::string clientVendor = glXGetClientString(display, GLX_VENDOR);

[piman, 2016/05/25 22:35:17]

nit: client_vendor

+  bool isMesa = clientVendor.find("Mesa") != std::string::npos;

[piman, 2016/05/25 22:35:17]

nit: is_mesa

+
+  const ContextCreationInfo* toTry = contextsToTry;

[piman, 2016/05/25 22:35:17]

nit: to_try

+  size_t toTryLength = arraysize(contextsToTry);

[piman, 2016/05/25 22:35:17]

nit: to_try_length

+  if (isMesa) {
+    toTry = mesaContextsToTry;
+    toTryLength = arraysize(mesaContextsToTry);
+  }
+
+  for (size_t i = 0; i < toTryLength; ++i) {
+    const ContextCreationInfo& info = toTry[i];
+    if (!GLSurfaceGLX::IsCreateContextES2ProfileSupported() &&
+        info.profileFlag == GLX_CONTEXT_ES2_PROFILE_BIT_EXT) {
+      continue;
+    }
+    GLXContext context = CreateContextAttribs(display, config, share,
+                                              info.version, info.profileFlag);
+    if (context != nullptr) {
+      return context;
+    }
+  }
+
+  return nullptr;
+}
+}
+
 GLContextGLX::GLContextGLX(GLShareGroup* share_group)
   : GLContextReal(share_group),
     context_(nullptr),
@@ -38,19 +166,9 @@ bool GLContextGLX::Initialize(
 
   if (GLSurfaceGLX::IsCreateContextSupported()) {
     DVLOG(1) << "GLX_ARB_create_context supported.";
-    std::vector<int> attribs;
-    if (GLSurfaceGLX::IsCreateContextRobustnessSupported()) {
-      DVLOG(1) << "GLX_ARB_create_context_robustness supported.";
-      attribs.push_back(GLX_CONTEXT_RESET_NOTIFICATION_STRATEGY_ARB);
-      attribs.push_back(GLX_LOSE_CONTEXT_ON_RESET_ARB);
-    }
-    attribs.push_back(0);
-    context_ = glXCreateContextAttribsARB(
-        display_,
-        static_cast<GLXFBConfig>(compatible_surface->GetConfig()),
-        share_handle,
-        True,
-        &attribs.front());
+    context_ = CreateHighestVersionContext(
+        display_, static_cast<GLXFBConfig>(compatible_surface->GetConfig()),
+        share_handle);
     if (!context_) {
       LOG(ERROR) << "Failed to create GL context with "
                  << "glXCreateContextAttribsARB.";