Add support for Khr_surfaceless_context.

ui/gl/gl_surface_egl.cc

Index: ui/gl/gl_surface_egl.cc
diff --git a/ui/gl/gl_surface_egl.cc b/ui/gl/gl_surface_egl.cc
index 7401fbb320745808b18ebf6da531782b2422e1b3..3a12d6fba06d0006707f8195175e9dfe2f2e70f8 100644
--- a/ui/gl/gl_surface_egl.cc
+++ b/ui/gl/gl_surface_egl.cc
@@ -54,6 +54,7 @@ EGLNativeDisplayType g_native_display;
 const char* g_egl_extensions = NULL;
 bool g_egl_create_context_robustness_supported = false;
 bool g_egl_sync_control_supported = false;
+bool g_egl_surfaceless_context = false;

[piman, 2013/10/31 20:07:54]

nit: g_egl_surfaceless_context_supported for consistency

[kalyank, 2013/10/31 22:15:27]

fixed.

 
 class EGLSyncControlVSyncProvider
     : public gfx::SyncControlVSyncProvider {
@@ -184,6 +185,26 @@ bool GLSurfaceEGL::InitializeOneOff() {
   g_egl_sync_control_supported =
       HasEGLExtension("EGL_CHROMIUM_sync_control");
 
+  // Check if SurfacelessEGL is supported.
+  g_egl_surfaceless_context = HasEGLExtension("EGL_KHR_surfaceless_context");
+  if (g_egl_surfaceless_context) {
+    // EGL_KHR_surfaceless_context is supported but ensure
+    // GL_OES_surfaceless_context is also supported. We need a current context
+    // to query for supported GL extensions.
+    scoped_refptr<GLSurface> surface = new SurfacelessEGL(Size(1, 1));
+    scoped_refptr<GLContext> context = GLContext::CreateGLContext(
+      NULL, surface.get(), PreferIntegratedGpu);
+    if (!context->MakeCurrent(surface.get()))
+      g_egl_surfaceless_context = false;
+
+    // Ensure context supports GL_OES_surfaceless_context.
+    if (g_egl_surfaceless_context) {
+      g_egl_surfaceless_context = context->HasExtension(
+          "GL_OES_surfaceless_context");
+      context->ReleaseCurrent(surface.get());
+    }
+  }
+
   initialized = true;
 
   return true;
@@ -593,6 +614,50 @@ PbufferGLSurfaceEGL::~PbufferGLSurfaceEGL() {
   Destroy();
 }
 
+SurfacelessEGL::SurfacelessEGL(const gfx::Size& size)
+    : size_(size) {
+}
+
+bool SurfacelessEGL::Initialize() {
+  return true;
+}
+
+void SurfacelessEGL::Destroy() {
+}
+
+EGLConfig SurfacelessEGL::GetConfig() {
+  return g_config;
+}
+
+bool SurfacelessEGL::IsOffscreen() {
+  return true;
+}
+
+bool SurfacelessEGL::SwapBuffers() {
+  NOTREACHED() << "Attempted to call SwapBuffers with SurfacelessEGL.";

[piman, 2013/10/31 20:07:54]

note: technically it can be reached if the (untrusted) client call SwapBuffers
on the offscreen context. Maybe LOG(ERROR) instead.

[kalyank, 2013/10/31 22:15:27]

fixed.

+  return false;
+}
+
+gfx::Size SurfacelessEGL::GetSize() {
+  return size_;
+}
+
+bool SurfacelessEGL::Resize(const gfx::Size& size) {
+  size_ = size;
+  return true;
+}
+
+EGLSurface SurfacelessEGL::GetHandle() {
+  return EGL_NO_SURFACE;
+}
+
+void* SurfacelessEGL::GetShareHandle() {
+  return NULL;
+}
+
+SurfacelessEGL::~SurfacelessEGL() {
+}
+
 #if defined(ANDROID) || defined(USE_OZONE)
 
 // A thin subclass of |GLSurfaceOSMesa| that can be used in place
@@ -681,8 +746,12 @@ GLSurface::CreateOffscreenGLSurface(const gfx::Size& size) {
       return surface;
     }
     case kGLImplementationEGLGLES2: {
-      scoped_refptr<PbufferGLSurfaceEGL> surface(
-          new PbufferGLSurfaceEGL(size));
+      scoped_refptr<GLSurface> surface;
+      if (g_egl_surfaceless_context)
+        surface = new SurfacelessEGL(size);

[piman, 2013/10/31 20:07:54]

So, what if the client really meant to have an offscreen backbuffer? Could we
make this choice based on, say, size being (0x0), and fix the callers? We pass
1x1 everywhere for historical reasons, but we should clean that up...

[kalyank, 2013/10/31 22:15:27]

I for now added the checks with 1,1 size. If no one has started working on it, I
can fix the callers and change the size to 0x0 in a separate CL?

+      else
+        surface = new PbufferGLSurfaceEGL(size);
+
       if (!surface->Initialize())
         return NULL;
       return surface;