Improve Ganesh helpers.

mojo/skia/ganesh_context.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_SKIA_GANESH_CONTEXT_H_
 #define MOJO_SKIA_GANESH_CONTEXT_H_
 
 #include "base/basictypes.h"
 #include "base/memory/weak_ptr.h"
 #include "mojo/gpu/gl_context.h"
 #include "skia/ext/refptr.h"
 #include "third_party/skia/include/gpu/GrContext.h"
 
-namespace gpu {
-namespace gles2 {
-class GLES2Interface;
-}
-}
+namespace mojo {
+namespace skia {
 
-namespace mojo {
-
+// Binds a Ganesh rendering context to a GL context.
+//
+// This object is not thread-safe.
 class GaneshContext : public GLContext::Observer {
  public:
+  // RAII style helper for executing code within a Ganesh environment.
+  //
+  // Note that Ganesh assumes that it owns the state of the GL Context
+  // for the duration while the scope is active.  Take care not to perform
+  // any significant low-level GL operations while in the Ganesh scope
+  // which might disrupt what Ganesh is doing!
+  //
+  // Entering a Ganesh scope recursively has no effect.  In particular,
+  // no state will be flushed.
   class Scope {
    public:
-    explicit Scope(GaneshContext*);
+    // Upon entry to the scope, makes the GL context active and resets
+    // the Ganesh context state.
+    explicit Scope(GaneshContext* context);
+
+    // Upon exit from the scope, flushes the Ganesh context state and
+    // restores the prior GL context.
     ~Scope();
 
    private:
-    gpu::gles2::GLES2Interface* previous_;
+    GaneshContext* context_;
   };
 
   explicit GaneshContext(base::WeakPtr<GLContext> gl_context);
   ~GaneshContext() override;
 
+  // Gets the underlying GL context.
+  const base::WeakPtr<GLContext>& gl_context() const { return gl_context_; }
+
+  // Gets the Ganesh renderer context.
   // Note: You must be in a GaneshContext::Scope to use GrContext.
-  GrContext* gr() const {
+  GrContext* gr_context() const {
     DCHECK(InScope());
-    return context_.get();
+    return gr_context_.get();
   }
 
  private:
   bool InScope() const;
   void OnContextLost() override;
+  void ReleaseContext();
+
+  void EnterScope();
+  void ExitScope();
 
   base::WeakPtr<GLContext> gl_context_;
-  skia::RefPtr<GrContext> context_;
+  ::skia::RefPtr<GrContext> gr_context_;
+
+  uint32_t scope_nest_count_ = 0u;
+  MGLContext previous_mgl_context_ = MGL_NO_CONTEXT;
 
   DISALLOW_COPY_AND_ASSIGN(GaneshContext);
 };
 
+}  // namespace skia
 }  // namespace mojo
 
 #endif  // MOJO_SKIA_GANESH_CONTEXT_H_