Add SkWGLExtensionInterface for dealing with WGL extensions
Review URL: http://codereview.appspot.com/5447059

git-svn-id: http://skia.googlecode.com/svn/trunk@2777 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/utils/SkWGL.h b/include/utils/SkWGL.h
new file mode 100644
index 0000000..35c93f6
--- /dev/null
+++ b/include/utils/SkWGL.h
@@ -0,0 +1,90 @@
+
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkRefCnt.h"
+
+#ifndef SkWGL_DEFINED
+#define SkWGL_DEFINED
+
+/**
+ * Working with WGL extensions can be a pain. Among the reasons is that You must
+ * have a GL context to get the proc addresses, but you want to use the procs to
+ * create a context in the first place. So you have to create a dummy GL ctx to
+ * get the proc addresses.
+ *
+ * This file helps by providing SkCreateWGLInterface(). It returns a struct of
+ * function pointers that it initializes. It also has a helper function to query
+ * for WGL extensions. It handles the fact that wglGetExtensionsString is itself
+ * an extension.
+ */
+
+#if !defined(WIN32_LEAN_AND_MEAN)
+    #define WIN32_LEAN_AND_MEAN
+    #define SK_LOCAL_LEAN_AND_MEAN
+#endif
+#include <Windows.h>
+#if defined(SK_LOCAL_LEAN_AND_MEAN)
+    #undef WIN32_LEAN_AND_MEAN
+    #undef SK_LOCAL_LEAN_AND_MEAN
+#endif
+
+#define SK_WGL_DRAW_TO_WINDOW_ARB                                   0x2001
+#define SK_WGL_ACCELERATION_ARB                                     0x2003
+#define SK_WGL_SUPPORT_OPENGL_ARB                                   0x2010
+#define SK_WGL_DOUBLE_BUFFER_ARB                                    0x2011
+#define SK_WGL_COLOR_BITS_ARB                                       0x2014
+#define SK_WGL_ALPHA_BITS_ARB                                       0x201B
+#define SK_WGL_STENCIL_BITS_ARB                                     0x2023
+#define SK_WGL_FULL_ACCELERATION_ARB                                0x2027
+#define SK_WGL_SAMPLE_BUFFERS_ARB                                   0x2041
+#define SK_WGL_SAMPLES_ARB                                          0x2042
+#define SK_WGL_CONTEXT_MAJOR_VERSION_ARB                            0x2091
+#define SK_WGL_CONTEXT_MINOR_VERSION_ARB                            0x2092
+#define SK_WGL_CONTEXT_LAYER_PLANE_ARB                              0x2093
+#define SK_WGL_CONTEXT_FLAGS_ARB                                    0x2094
+#define SK_WGL_CONTEXT_PROFILE_MASK_ARB                             0x9126
+#define SK_WGL_CONTEXT_DEBUG_BIT_ARB                                0x0001
+#define SK_WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB                   0x0002
+#define SK_WGL_CONTEXT_CORE_PROFILE_BIT_ARB                         0x00000001
+#define SK_WGL_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB                0x00000002
+#define SK_WGL_CONTEXT_ES2_PROFILE_BIT_EXT                          0x00000004
+#define SK_ERROR_INVALID_VERSION_ARB                                0x2095
+#define SK_ERROR_INVALID_PROFILE_ARB                                0x2096
+
+class SkWGLExtensions {
+public:
+    SkWGLExtensions();
+    /**
+     * Determines if an extensions is available for a given DC.
+     * WGL_ARB_extensions_string is considered a prerequisite for all other
+     * extensions. It is necessary to check this before calling other class
+     * functions.
+     */
+    bool hasExtension(HDC dc, const char* ext) const;
+
+    const char* getExtensionsString(HDC hdc) const;
+    BOOL choosePixelFormat(HDC hdc, const int*, const FLOAT*, UINT, int*, UINT*) const;
+    BOOL getPixelFormatAttribiv(HDC, int, int, UINT, const int*, int*) const;
+    BOOL getPixelFormatAttribfv(HDC hdc, int, int, UINT, const int*, FLOAT*) const;
+    HGLRC createContextAttribs(HDC, HGLRC, const int *) const;
+
+private:
+    typedef const char* (WINAPI *GetExtensionsStringProc)(HDC hdc);
+    typedef BOOL (WINAPI *ChoosePixelFormatProc)(HDC 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 *);
+
+    GetExtensionsStringProc fGetExtensionsString;
+    ChoosePixelFormatProc fChoosePixelFormat;
+    GetPixelFormatAttribfvProc fGetPixelFormatAttribfv;
+    GetPixelFormatAttribivProc fGetPixelFormatAttribiv;
+    CreateContextAttribsProc fCreateContextAttribs;
+};
+
+#endif