When performing offscreen rendering on windows, attempt to use a pbuffer context.

include/utils/SkWGL.h

Index: include/utils/SkWGL.h
diff --git a/include/utils/SkWGL.h b/include/utils/SkWGL.h
index 5272f17c87088b58ef3148824c0ca82de962e8c9..d502eb0aa70259082c124177f8760a057f13182b 100644
--- a/include/utils/SkWGL.h
+++ b/include/utils/SkWGL.h
@@ -56,6 +56,8 @@
 #define SK_ERROR_INVALID_VERSION                    0x2095
 #define SK_ERROR_INVALID_PROFILE                    0x2096
 
+DECLARE_HANDLE(HPBUFFER);
+
 class SkWGLExtensions {
 public:
     SkWGLExtensions();
@@ -73,6 +75,13 @@ public:
     BOOL getPixelFormatAttribfv(HDC hdc, int, int, UINT, const int*, FLOAT*) const;
     HGLRC createContextAttribs(HDC, HGLRC, const int *) const;
 
+    BOOL swapInterval(int interval) const;
+
+    HPBUFFER createPbuffer(HDC, int , int, int, const int*) const;
+    HDC getPbufferDC(HPBUFFER) const;
+    int releasePbufferDC(HPBUFFER, HDC) const;
+    BOOL destroyPbuffer(HPBUFFER) const;
+
     /**
      * WGL doesn't have precise rules for the ordering of formats returned
      * by wglChoosePixelFormat. This function helps choose among the set of
@@ -89,19 +98,29 @@ public:
     int selectFormat(const int formats[],
                      int formatCount,
                      HDC dc,
-                     int desiredSampleCount);
+                     int desiredSampleCount) const;
 private:
-    typedef const char* (WINAPI *GetExtensionsStringProc)(HDC hdc);
-    typedef BOOL (WINAPI *ChoosePixelFormatProc)(HDC hdc, const int *, const FLOAT *, UINT, int *, UINT *);
+    typedef const char* (WINAPI *GetExtensionsStringProc)(HDC);
+    typedef BOOL (WINAPI *ChoosePixelFormatProc)(HDC, const int *, const FLOAT *, UINT, int *, UINT *);
     typedef BOOL (WINAPI *GetPixelFormatAttribivProc)(HDC, int, int, UINT, const int*, int*);
-    typedef BOOL (WINAPI *GetPixelFormatAttribfvProc)(HDC hdc, int, int, UINT, const int*, FLOAT*);
-    typedef HGLRC (WINAPI *CreateContextAttribsProc)(HDC hDC, HGLRC, const int *);
+    typedef BOOL (WINAPI *GetPixelFormatAttribfvProc)(HDC, int, int, UINT, const int*, FLOAT*);
+    typedef HGLRC (WINAPI *CreateContextAttribsProc)(HDC, HGLRC, const int *);
+    typedef BOOL (WINAPI* SwapIntervalProc)(int);
+    typedef HPBUFFER (WINAPI* CreatePbufferProc)(HDC, int , int, int, const int*);
+    typedef HDC (WINAPI* GetPbufferDCProc)(HPBUFFER);
+    typedef int (WINAPI* ReleasePbufferDCProc)(HPBUFFER, HDC);
+    typedef BOOL (WINAPI* DestroyPbufferProc)(HPBUFFER);
 
     GetExtensionsStringProc fGetExtensionsString;
     ChoosePixelFormatProc fChoosePixelFormat;
     GetPixelFormatAttribfvProc fGetPixelFormatAttribfv;
     GetPixelFormatAttribivProc fGetPixelFormatAttribiv;
     CreateContextAttribsProc fCreateContextAttribs;
+    SwapIntervalProc fSwapInterval;
+    CreatePbufferProc fCreatePbuffer;
+    GetPbufferDCProc fGetPbufferDC;
+    ReleasePbufferDCProc fReleasePbufferDC;
+    DestroyPbufferProc fDestroyPbuffer;
 };
 
 enum SkWGLContextRequest {
@@ -122,4 +141,28 @@ enum SkWGLContextRequest {
  */
 HGLRC SkCreateWGLContext(HDC dc, int msaaSampleCount, SkWGLContextRequest context);
 
+/**
+ * Helper class for creating a pbuffer context and deleting all the handles when finished. This
+ * requires that a device context has been created. However, the pbuffer gets its own device
+ * context. The original device context can be released once the pbuffer context is created.
+ */
+class SkWGLPbufferContext : public SkRefCnt {
+public:
+    static SkWGLPbufferContext* Create(HDC parentDC, int msaaSampleCount,
+                                       SkWGLContextRequest contextType);
+
+    virtual ~SkWGLPbufferContext();
+
+    HDC getDC() const { return fDC; }
+    HGLRC getGLRC() const { return fGLRC; }
+
+private:
+    SkWGLPbufferContext(HPBUFFER pbuffer, HDC dc, HGLRC glrc);
+
+    HPBUFFER        fPbuffer;
+    HDC             fDC;
+    HGLRC           fGLRC;
+    SkWGLExtensions fExtensions;
+};
+
 #endif