src/utils/win/SkWGL_win.cpp - platform/external/skia - Gitiles

 /*
  * 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 "SkTypes.h"
 #if defined(SK_BUILD_FOR_WIN32)

 #include "SkWGL.h"

 #include "SkTDArray.h"
 #include "SkTSearch.h"
 #include "SkTSort.h"

 bool SkWGLExtensions::hasExtension(HDC dc, const char* ext) const {
     if (nullptr == this->fGetExtensionsString) {
         return false;
     }
     if (!strcmp("WGL_ARB_extensions_string", ext)) {
         return true;
     }
     const char* extensionString = this->getExtensionsString(dc);
     size_t extLength = strlen(ext);

     while (true) {
         size_t n = strcspn(extensionString, " ");
         if (n == extLength && 0 == strncmp(ext, extensionString, n)) {
             return true;
         }
         if (0 == extensionString[n]) {
             return false;
         }
         extensionString += n+1;
     }

     return false;
 }

 const char* SkWGLExtensions::getExtensionsString(HDC hdc) const {
     return fGetExtensionsString(hdc);
 }

 BOOL SkWGLExtensions::choosePixelFormat(HDC hdc,
                                         const int* piAttribIList,
                                         const FLOAT* pfAttribFList,
                                         UINT nMaxFormats,
                                         int* piFormats,
                                         UINT* nNumFormats) const {
     return fChoosePixelFormat(hdc, piAttribIList, pfAttribFList,
                               nMaxFormats, piFormats, nNumFormats);
 }

 BOOL SkWGLExtensions::getPixelFormatAttribiv(HDC hdc,
                                              int iPixelFormat,
                                              int iLayerPlane,
                                              UINT nAttributes,
                                              const int *piAttributes,
                                              int *piValues) const {
     return fGetPixelFormatAttribiv(hdc, iPixelFormat, iLayerPlane,
                                    nAttributes, piAttributes, piValues);
 }

 BOOL SkWGLExtensions::getPixelFormatAttribfv(HDC hdc,
                                              int iPixelFormat,
                                              int iLayerPlane,
                                              UINT nAttributes,
                                              const int *piAttributes,
                                              float *pfValues) const {
     return fGetPixelFormatAttribfv(hdc, iPixelFormat, iLayerPlane,
                                    nAttributes, piAttributes, pfValues);
 }
 HGLRC SkWGLExtensions::createContextAttribs(HDC hDC,
                                             HGLRC hShareContext,
                                             const int *attribList) const {
     return fCreateContextAttribs(hDC, hShareContext, attribList);
 }

 BOOL SkWGLExtensions::swapInterval(int interval) const {
     return fSwapInterval(interval);
 }

 HPBUFFER SkWGLExtensions::createPbuffer(HDC hDC,
                                         int iPixelFormat,
                                         int iWidth,
                                         int iHeight,
                                         const int *piAttribList) const {
     return fCreatePbuffer(hDC, iPixelFormat, iWidth, iHeight, piAttribList);
 }

 HDC SkWGLExtensions::getPbufferDC(HPBUFFER hPbuffer) const {
     return fGetPbufferDC(hPbuffer);
 }

 int SkWGLExtensions::releasePbufferDC(HPBUFFER hPbuffer, HDC hDC) const {
     return fReleasePbufferDC(hPbuffer, hDC);
 }

 BOOL SkWGLExtensions::destroyPbuffer(HPBUFFER hPbuffer) const {
     return fDestroyPbuffer(hPbuffer);
 }

 namespace {

 struct PixelFormat {
     int fFormat;
     int fSampleCnt;
     int fChoosePixelFormatRank;
 };

 bool pf_less(const PixelFormat& a, const PixelFormat& b) {
     if (a.fSampleCnt < b.fSampleCnt) {
         return true;
     } else if (b.fSampleCnt < a.fSampleCnt) {
         return false;
     } else if (a.fChoosePixelFormatRank < b.fChoosePixelFormatRank) {
         return true;
     }
     return false;
 }
 }

 int SkWGLExtensions::selectFormat(const int formats[],
                                   int formatCount,
                                   HDC dc,
                                   int desiredSampleCount) const {
     if (formatCount <= 0) {
         return -1;
     }
     PixelFormat desiredFormat = {
         0,
         desiredSampleCount,
         0,
     };
     SkTDArray<PixelFormat> rankedFormats;
     rankedFormats.setCount(formatCount);
     for (int i = 0; i < formatCount; ++i) {
         static const int kQueryAttr = SK_WGL_SAMPLES;
         int numSamples;
         this->getPixelFormatAttribiv(dc,
                                      formats[i],
                                      0,
                                      1,
                                      &kQueryAttr,
                                      &numSamples);
         rankedFormats[i].fFormat =  formats[i];
         rankedFormats[i].fSampleCnt = numSamples;
         rankedFormats[i].fChoosePixelFormatRank = i;
     }
     SkTQSort(rankedFormats.begin(),
              rankedFormats.begin() + rankedFormats.count() - 1,
              SkTLessFunctionToFunctorAdaptor<PixelFormat, pf_less>());
     int idx = SkTSearch<PixelFormat, pf_less>(rankedFormats.begin(),
                                               rankedFormats.count(),
                                               desiredFormat,
                                               sizeof(PixelFormat));
     if (idx < 0) {
         idx = ~idx;
     }
     return rankedFormats[idx].fFormat;
 }


 namespace {

 #if defined(UNICODE)
     #define STR_LIT(X) L## #X
 #else
     #define STR_LIT(X) #X
 #endif

 #define DUMMY_CLASS STR_LIT("DummyClass")

 HWND create_dummy_window() {
     HMODULE module = GetModuleHandle(nullptr);
     HWND dummy;
     RECT windowRect;
     windowRect.left = 0;
     windowRect.right = 8;
     windowRect.top = 0;
     windowRect.bottom = 8;

     WNDCLASS wc;

     wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
     wc.lpfnWndProc = (WNDPROC) DefWindowProc;
     wc.cbClsExtra = 0;
     wc.cbWndExtra = 0;
     wc.hInstance = module;
     wc.hIcon = LoadIcon(nullptr, IDI_WINLOGO);
     wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
     wc.hbrBackground = nullptr;
     wc.lpszMenuName = nullptr;
     wc.lpszClassName = DUMMY_CLASS;

     if(!RegisterClass(&wc)) {
         return 0;
     }

     DWORD style, exStyle;
     exStyle = WS_EX_CLIENTEDGE;
     style = WS_SYSMENU;

     AdjustWindowRectEx(&windowRect, style, false, exStyle);
     if(!(dummy = CreateWindowEx(exStyle,
                                 DUMMY_CLASS,
                                 STR_LIT("DummyWindow"),
                                 WS_CLIPSIBLINGS | WS_CLIPCHILDREN | style,
                                 0, 0,
                                 windowRect.right-windowRect.left,
                                 windowRect.bottom-windowRect.top,
                                 nullptr, nullptr,
                                 module,
                                 nullptr))) {
         UnregisterClass(DUMMY_CLASS, module);
         return nullptr;
     }
     ShowWindow(dummy, SW_HIDE);

     return dummy;
 }

 void destroy_dummy_window(HWND dummy) {
     DestroyWindow(dummy);
     HMODULE module = GetModuleHandle(nullptr);
     UnregisterClass(DUMMY_CLASS, module);
 }
 }

 #define GET_PROC(NAME, SUFFIX) f##NAME = \
                      (##NAME##Proc) wglGetProcAddress("wgl" #NAME #SUFFIX)

 SkWGLExtensions::SkWGLExtensions()
     : fGetExtensionsString(nullptr)
     , fChoosePixelFormat(nullptr)
     , fGetPixelFormatAttribfv(nullptr)
     , fGetPixelFormatAttribiv(nullptr)
     , fCreateContextAttribs(nullptr)
     , fSwapInterval(nullptr)
     , fCreatePbuffer(nullptr)
     , fGetPbufferDC(nullptr)
     , fReleasePbufferDC(nullptr)
     , fDestroyPbuffer(nullptr)
  {
     HDC prevDC = wglGetCurrentDC();
     HGLRC prevGLRC = wglGetCurrentContext();

     PIXELFORMATDESCRIPTOR dummyPFD;

     ZeroMemory(&dummyPFD, sizeof(dummyPFD));
     dummyPFD.nSize = sizeof(dummyPFD);
     dummyPFD.nVersion = 1;
     dummyPFD.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL;
     dummyPFD.iPixelType = PFD_TYPE_RGBA;
     dummyPFD.cColorBits  = 32;
     dummyPFD.cDepthBits  = 0;
     dummyPFD.cStencilBits = 8;
     dummyPFD.iLayerType = PFD_MAIN_PLANE;
     HWND dummyWND = create_dummy_window();
     if (dummyWND) {
         HDC dummyDC = GetDC(dummyWND);
         int dummyFormat = ChoosePixelFormat(dummyDC, &dummyPFD);
         SetPixelFormat(dummyDC, dummyFormat, &dummyPFD);
         HGLRC dummyGLRC = wglCreateContext(dummyDC);
         SkASSERT(dummyGLRC);
         wglMakeCurrent(dummyDC, dummyGLRC);

         GET_PROC(GetExtensionsString, ARB);
         GET_PROC(ChoosePixelFormat, ARB);
         GET_PROC(GetPixelFormatAttribiv, ARB);
         GET_PROC(GetPixelFormatAttribfv, ARB);
         GET_PROC(CreateContextAttribs, ARB);
         GET_PROC(SwapInterval, EXT);
         GET_PROC(CreatePbuffer, ARB);
         GET_PROC(GetPbufferDC, ARB);
         GET_PROC(ReleasePbufferDC, ARB);
         GET_PROC(DestroyPbuffer, ARB);

         wglMakeCurrent(dummyDC, nullptr);
         wglDeleteContext(dummyGLRC);
         destroy_dummy_window(dummyWND);
     }

     wglMakeCurrent(prevDC, prevGLRC);
 }

 ///////////////////////////////////////////////////////////////////////////////

 static void get_pixel_formats_to_try(HDC dc, const SkWGLExtensions& extensions,
                                      bool doubleBuffered, int msaaSampleCount, bool deepColor,
                                      int formatsToTry[2]) {
     auto appendAttr = [](SkTDArray<int>& attrs, int attr, int value) {
         attrs.push(attr);
         attrs.push(value);
     };

     SkTDArray<int> iAttrs;
     appendAttr(iAttrs, SK_WGL_DRAW_TO_WINDOW, TRUE);
     appendAttr(iAttrs, SK_WGL_DOUBLE_BUFFER, (doubleBuffered ? TRUE : FALSE));
     appendAttr(iAttrs, SK_WGL_ACCELERATION, SK_WGL_FULL_ACCELERATION);
     appendAttr(iAttrs, SK_WGL_SUPPORT_OPENGL, TRUE);
     if (deepColor) {
         appendAttr(iAttrs, SK_WGL_RED_BITS, 10);
         appendAttr(iAttrs, SK_WGL_GREEN_BITS, 10);
         appendAttr(iAttrs, SK_WGL_BLUE_BITS, 10);
         appendAttr(iAttrs, SK_WGL_ALPHA_BITS, 2);
     } else {
         appendAttr(iAttrs, SK_WGL_COLOR_BITS, 24);
         appendAttr(iAttrs, SK_WGL_ALPHA_BITS, 8);
     }
     appendAttr(iAttrs, SK_WGL_STENCIL_BITS, 8);

     float fAttrs[] = {0, 0};

     // Get a MSAA format if requested and possible.
     if (msaaSampleCount > 0 &&
         extensions.hasExtension(dc, "WGL_ARB_multisample")) {
         SkTDArray<int> msaaIAttrs = iAttrs;
         appendAttr(msaaIAttrs, SK_WGL_SAMPLE_BUFFERS, TRUE);
         appendAttr(msaaIAttrs, SK_WGL_SAMPLES, msaaSampleCount);
         appendAttr(msaaIAttrs, 0, 0);
         unsigned int num;
         int formats[64];
         extensions.choosePixelFormat(dc, msaaIAttrs.begin(), fAttrs, 64, formats, &num);
         num = SkTMin(num, 64U);
         formatsToTry[0] = extensions.selectFormat(formats, num, dc, msaaSampleCount);
     }

     // Get a non-MSAA format
     int* format = -1 == formatsToTry[0] ? &formatsToTry[0] : &formatsToTry[1];
     unsigned int num;
     appendAttr(iAttrs, 0, 0);
     extensions.choosePixelFormat(dc, iAttrs.begin(), fAttrs, 1, format, &num);
 }

 static HGLRC create_gl_context(HDC dc, SkWGLExtensions extensions, SkWGLContextRequest contextType) {
     HDC prevDC = wglGetCurrentDC();
     HGLRC prevGLRC = wglGetCurrentContext();

     HGLRC glrc = nullptr;
     if (kGLES_SkWGLContextRequest == contextType) {
         if (!extensions.hasExtension(dc, "WGL_EXT_create_context_es2_profile")) {
             wglMakeCurrent(prevDC, prevGLRC);
             return nullptr;
         }
         static const int glesAttribs[] = {
             SK_WGL_CONTEXT_MAJOR_VERSION, 3,
             SK_WGL_CONTEXT_MINOR_VERSION, 0,
             SK_WGL_CONTEXT_PROFILE_MASK,  SK_WGL_CONTEXT_ES2_PROFILE_BIT,
             0,
         };
         glrc = extensions.createContextAttribs(dc, nullptr, glesAttribs);
         if (nullptr == glrc) {
             wglMakeCurrent(prevDC, prevGLRC);
             return nullptr;
         }
     } else {
         if (kGLPreferCoreProfile_SkWGLContextRequest == contextType &&
             extensions.hasExtension(dc, "WGL_ARB_create_context")) {
             static const int kCoreGLVersions[] = {
                 4, 3,
                 4, 2,
                 4, 1,
                 4, 0,
                 3, 3,
                 3, 2,
             };
             int coreProfileAttribs[] = {
                 SK_WGL_CONTEXT_MAJOR_VERSION, -1,
                 SK_WGL_CONTEXT_MINOR_VERSION, -1,
                 SK_WGL_CONTEXT_PROFILE_MASK,  SK_WGL_CONTEXT_CORE_PROFILE_BIT,
                 0,
             };
             for (int v = 0; v < SK_ARRAY_COUNT(kCoreGLVersions) / 2; ++v) {
                 coreProfileAttribs[1] = kCoreGLVersions[2 * v];
                 coreProfileAttribs[3] = kCoreGLVersions[2 * v + 1];
                 glrc = extensions.createContextAttribs(dc, nullptr, coreProfileAttribs);
                 if (glrc) {
                     break;
                 }
             }
         }
     }

     if (nullptr == glrc) {
         glrc = wglCreateContext(dc);
     }
     SkASSERT(glrc);

     wglMakeCurrent(prevDC, prevGLRC);

     // This might help make the context non-vsynced.
     if (extensions.hasExtension(dc, "WGL_EXT_swap_control")) {
         extensions.swapInterval(-1);
     }
     return glrc;
 }

 HGLRC SkCreateWGLContext(HDC dc, int msaaSampleCount, bool deepColor,
                          SkWGLContextRequest contextType) {
     SkWGLExtensions extensions;
     if (!extensions.hasExtension(dc, "WGL_ARB_pixel_format")) {
         return nullptr;
     }

     BOOL set = FALSE;

     int pixelFormatsToTry[] = { -1, -1 };
     get_pixel_formats_to_try(dc, extensions, true, msaaSampleCount, deepColor, pixelFormatsToTry);
     for (int f = 0;
          !set && -1 != pixelFormatsToTry[f] && f < SK_ARRAY_COUNT(pixelFormatsToTry);
          ++f) {
         PIXELFORMATDESCRIPTOR pfd;
         DescribePixelFormat(dc, pixelFormatsToTry[f], sizeof(pfd), &pfd);
         set = SetPixelFormat(dc, pixelFormatsToTry[f], &pfd);
     }

     if (!set) {
         return nullptr;
     }

     return create_gl_context(dc, extensions, contextType);}

 SkWGLPbufferContext* SkWGLPbufferContext::Create(HDC parentDC, int msaaSampleCount,
                                                  SkWGLContextRequest contextType) {
     SkWGLExtensions extensions;
     if (!extensions.hasExtension(parentDC, "WGL_ARB_pixel_format") ||
         !extensions.hasExtension(parentDC, "WGL_ARB_pbuffer")) {
         return nullptr;
     }

     // try for single buffer first
     for (int dblBuffer = 0; dblBuffer < 2; ++dblBuffer) {
         int pixelFormatsToTry[] = { -1, -1 };
         get_pixel_formats_to_try(parentDC, extensions, (0 != dblBuffer), msaaSampleCount,
                                  false, pixelFormatsToTry);
         for (int f = 0; -1 != pixelFormatsToTry[f] && f < SK_ARRAY_COUNT(pixelFormatsToTry); ++f) {
             HPBUFFER pbuf = extensions.createPbuffer(parentDC, pixelFormatsToTry[f], 1, 1, nullptr);
             if (0 != pbuf) {
                 HDC dc = extensions.getPbufferDC(pbuf);
                 if (dc) {
                     HGLRC glrc = create_gl_context(dc, extensions, contextType);
                     if (glrc) {
                         return new SkWGLPbufferContext(pbuf, dc, glrc);
                     }
                     extensions.releasePbufferDC(pbuf, dc);
                 }
                 extensions.destroyPbuffer(pbuf);
             }
         }
     }
     return nullptr;
 }

 SkWGLPbufferContext::~SkWGLPbufferContext() {
     SkASSERT(fExtensions.hasExtension(fDC, "WGL_ARB_pbuffer"));
     wglDeleteContext(fGLRC);
     fExtensions.releasePbufferDC(fPbuffer, fDC);
     fExtensions.destroyPbuffer(fPbuffer);
 }

 SkWGLPbufferContext::SkWGLPbufferContext(HPBUFFER pbuffer, HDC dc, HGLRC glrc)
     : fPbuffer(pbuffer)
     , fDC(dc)
     , fGLRC(glrc) {
 }

 #endif//defined(SK_BUILD_FOR_WIN32)
	/*
	* 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 "SkTypes.h"
	#if defined(SK_BUILD_FOR_WIN32)

	#include "SkWGL.h"

	#include "SkTDArray.h"
	#include "SkTSearch.h"
	#include "SkTSort.h"

	bool SkWGLExtensions::hasExtension(HDC dc, const char* ext) const {
	if (nullptr == this->fGetExtensionsString) {
	return false;
	}
	if (!strcmp("WGL_ARB_extensions_string", ext)) {
	return true;
	}
	const char* extensionString = this->getExtensionsString(dc);
	size_t extLength = strlen(ext);

	while (true) {
	size_t n = strcspn(extensionString, " ");
	if (n == extLength && 0 == strncmp(ext, extensionString, n)) {
	return true;
	}
	if (0 == extensionString[n]) {
	return false;
	}
	extensionString += n+1;
	}

	return false;
	}

	const char* SkWGLExtensions::getExtensionsString(HDC hdc) const {
	return fGetExtensionsString(hdc);
	}

	BOOL SkWGLExtensions::choosePixelFormat(HDC hdc,
	const int* piAttribIList,
	const FLOAT* pfAttribFList,
	UINT nMaxFormats,
	int* piFormats,
	UINT* nNumFormats) const {
	return fChoosePixelFormat(hdc, piAttribIList, pfAttribFList,
	nMaxFormats, piFormats, nNumFormats);
	}

	BOOL SkWGLExtensions::getPixelFormatAttribiv(HDC hdc,
	int iPixelFormat,
	int iLayerPlane,
	UINT nAttributes,
	const int *piAttributes,
	int *piValues) const {
	return fGetPixelFormatAttribiv(hdc, iPixelFormat, iLayerPlane,
	nAttributes, piAttributes, piValues);
	}

	BOOL SkWGLExtensions::getPixelFormatAttribfv(HDC hdc,
	int iPixelFormat,
	int iLayerPlane,
	UINT nAttributes,
	const int *piAttributes,
	float *pfValues) const {
	return fGetPixelFormatAttribfv(hdc, iPixelFormat, iLayerPlane,
	nAttributes, piAttributes, pfValues);
	}
	HGLRC SkWGLExtensions::createContextAttribs(HDC hDC,
	HGLRC hShareContext,
	const int *attribList) const {
	return fCreateContextAttribs(hDC, hShareContext, attribList);
	}

	BOOL SkWGLExtensions::swapInterval(int interval) const {
	return fSwapInterval(interval);
	}

	HPBUFFER SkWGLExtensions::createPbuffer(HDC hDC,
	int iPixelFormat,
	int iWidth,
	int iHeight,
	const int *piAttribList) const {
	return fCreatePbuffer(hDC, iPixelFormat, iWidth, iHeight, piAttribList);
	}

	HDC SkWGLExtensions::getPbufferDC(HPBUFFER hPbuffer) const {
	return fGetPbufferDC(hPbuffer);
	}

	int SkWGLExtensions::releasePbufferDC(HPBUFFER hPbuffer, HDC hDC) const {
	return fReleasePbufferDC(hPbuffer, hDC);
	}

	BOOL SkWGLExtensions::destroyPbuffer(HPBUFFER hPbuffer) const {
	return fDestroyPbuffer(hPbuffer);
	}

	namespace {

	struct PixelFormat {
	int fFormat;
	int fSampleCnt;
	int fChoosePixelFormatRank;
	};

	bool pf_less(const PixelFormat& a, const PixelFormat& b) {
	if (a.fSampleCnt < b.fSampleCnt) {
	return true;
	} else if (b.fSampleCnt < a.fSampleCnt) {
	return false;
	} else if (a.fChoosePixelFormatRank < b.fChoosePixelFormatRank) {
	return true;
	}
	return false;
	}
	}

	int SkWGLExtensions::selectFormat(const int formats[],
	int formatCount,
	HDC dc,
	int desiredSampleCount) const {
	if (formatCount <= 0) {
	return -1;
	}
	PixelFormat desiredFormat = {
	0,
	desiredSampleCount,
	0,
	};
	SkTDArray<PixelFormat> rankedFormats;
	rankedFormats.setCount(formatCount);
	for (int i = 0; i < formatCount; ++i) {
	static const int kQueryAttr = SK_WGL_SAMPLES;
	int numSamples;
	this->getPixelFormatAttribiv(dc,
	formats[i],
	0,
	1,
	&kQueryAttr,
	&numSamples);
	rankedFormats[i].fFormat = formats[i];
	rankedFormats[i].fSampleCnt = numSamples;
	rankedFormats[i].fChoosePixelFormatRank = i;
	}
	SkTQSort(rankedFormats.begin(),
	rankedFormats.begin() + rankedFormats.count() - 1,
	SkTLessFunctionToFunctorAdaptor<PixelFormat, pf_less>());
	int idx = SkTSearch<PixelFormat, pf_less>(rankedFormats.begin(),
	rankedFormats.count(),
	desiredFormat,
	sizeof(PixelFormat));
	if (idx < 0) {
	idx = ~idx;
	}
	return rankedFormats[idx].fFormat;
	}


	namespace {

	#if defined(UNICODE)
	#define STR_LIT(X) L## #X
	#else
	#define STR_LIT(X) #X
	#endif

	#define DUMMY_CLASS STR_LIT("DummyClass")

	HWND create_dummy_window() {
	HMODULE module = GetModuleHandle(nullptr);
	HWND dummy;
	RECT windowRect;
	windowRect.left = 0;
	windowRect.right = 8;
	windowRect.top = 0;
	windowRect.bottom = 8;

	WNDCLASS wc;

	wc.style = CS_HREDRAW \| CS_VREDRAW \| CS_OWNDC;
	wc.lpfnWndProc = (WNDPROC) DefWindowProc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hInstance = module;
	wc.hIcon = LoadIcon(nullptr, IDI_WINLOGO);
	wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
	wc.hbrBackground = nullptr;
	wc.lpszMenuName = nullptr;
	wc.lpszClassName = DUMMY_CLASS;

	if(!RegisterClass(&wc)) {
	return 0;
	}

	DWORD style, exStyle;
	exStyle = WS_EX_CLIENTEDGE;
	style = WS_SYSMENU;

	AdjustWindowRectEx(&windowRect, style, false, exStyle);
	if(!(dummy = CreateWindowEx(exStyle,
	DUMMY_CLASS,
	STR_LIT("DummyWindow"),
	WS_CLIPSIBLINGS \| WS_CLIPCHILDREN \| style,
	0, 0,
	windowRect.right-windowRect.left,
	windowRect.bottom-windowRect.top,
	nullptr, nullptr,
	module,
	nullptr))) {
	UnregisterClass(DUMMY_CLASS, module);
	return nullptr;
	}
	ShowWindow(dummy, SW_HIDE);

	return dummy;
	}

	void destroy_dummy_window(HWND dummy) {
	DestroyWindow(dummy);
	HMODULE module = GetModuleHandle(nullptr);
	UnregisterClass(DUMMY_CLASS, module);
	}
	}

	#define GET_PROC(NAME, SUFFIX) f##NAME = \
	(##NAME##Proc) wglGetProcAddress("wgl" #NAME #SUFFIX)

	SkWGLExtensions::SkWGLExtensions()
	: fGetExtensionsString(nullptr)
	, fChoosePixelFormat(nullptr)
	, fGetPixelFormatAttribfv(nullptr)
	, fGetPixelFormatAttribiv(nullptr)
	, fCreateContextAttribs(nullptr)
	, fSwapInterval(nullptr)
	, fCreatePbuffer(nullptr)
	, fGetPbufferDC(nullptr)
	, fReleasePbufferDC(nullptr)
	, fDestroyPbuffer(nullptr)
	{
	HDC prevDC = wglGetCurrentDC();
	HGLRC prevGLRC = wglGetCurrentContext();

	PIXELFORMATDESCRIPTOR dummyPFD;

	ZeroMemory(&dummyPFD, sizeof(dummyPFD));
	dummyPFD.nSize = sizeof(dummyPFD);
	dummyPFD.nVersion = 1;
	dummyPFD.dwFlags = PFD_DRAW_TO_WINDOW \| PFD_SUPPORT_OPENGL;
	dummyPFD.iPixelType = PFD_TYPE_RGBA;
	dummyPFD.cColorBits = 32;
	dummyPFD.cDepthBits = 0;
	dummyPFD.cStencilBits = 8;
	dummyPFD.iLayerType = PFD_MAIN_PLANE;
	HWND dummyWND = create_dummy_window();
	if (dummyWND) {
	HDC dummyDC = GetDC(dummyWND);
	int dummyFormat = ChoosePixelFormat(dummyDC, &dummyPFD);
	SetPixelFormat(dummyDC, dummyFormat, &dummyPFD);
	HGLRC dummyGLRC = wglCreateContext(dummyDC);
	SkASSERT(dummyGLRC);
	wglMakeCurrent(dummyDC, dummyGLRC);

	GET_PROC(GetExtensionsString, ARB);
	GET_PROC(ChoosePixelFormat, ARB);
	GET_PROC(GetPixelFormatAttribiv, ARB);
	GET_PROC(GetPixelFormatAttribfv, ARB);
	GET_PROC(CreateContextAttribs, ARB);
	GET_PROC(SwapInterval, EXT);
	GET_PROC(CreatePbuffer, ARB);
	GET_PROC(GetPbufferDC, ARB);
	GET_PROC(ReleasePbufferDC, ARB);
	GET_PROC(DestroyPbuffer, ARB);

	wglMakeCurrent(dummyDC, nullptr);
	wglDeleteContext(dummyGLRC);
	destroy_dummy_window(dummyWND);
	}

	wglMakeCurrent(prevDC, prevGLRC);
	}

	///////////////////////////////////////////////////////////////////////////////

	static void get_pixel_formats_to_try(HDC dc, const SkWGLExtensions& extensions,
	bool doubleBuffered, int msaaSampleCount, bool deepColor,
	int formatsToTry[2]) {
	auto appendAttr = [](SkTDArray<int>& attrs, int attr, int value) {
	attrs.push(attr);
	attrs.push(value);
	};

	SkTDArray<int> iAttrs;
	appendAttr(iAttrs, SK_WGL_DRAW_TO_WINDOW, TRUE);
	appendAttr(iAttrs, SK_WGL_DOUBLE_BUFFER, (doubleBuffered ? TRUE : FALSE));
	appendAttr(iAttrs, SK_WGL_ACCELERATION, SK_WGL_FULL_ACCELERATION);
	appendAttr(iAttrs, SK_WGL_SUPPORT_OPENGL, TRUE);
	if (deepColor) {
	appendAttr(iAttrs, SK_WGL_RED_BITS, 10);
	appendAttr(iAttrs, SK_WGL_GREEN_BITS, 10);
	appendAttr(iAttrs, SK_WGL_BLUE_BITS, 10);
	appendAttr(iAttrs, SK_WGL_ALPHA_BITS, 2);
	} else {
	appendAttr(iAttrs, SK_WGL_COLOR_BITS, 24);
	appendAttr(iAttrs, SK_WGL_ALPHA_BITS, 8);
	}
	appendAttr(iAttrs, SK_WGL_STENCIL_BITS, 8);

	float fAttrs[] = {0, 0};

	// Get a MSAA format if requested and possible.
	if (msaaSampleCount > 0 &&
	extensions.hasExtension(dc, "WGL_ARB_multisample")) {
	SkTDArray<int> msaaIAttrs = iAttrs;
	appendAttr(msaaIAttrs, SK_WGL_SAMPLE_BUFFERS, TRUE);
	appendAttr(msaaIAttrs, SK_WGL_SAMPLES, msaaSampleCount);
	appendAttr(msaaIAttrs, 0, 0);
	unsigned int num;
	int formats[64];
	extensions.choosePixelFormat(dc, msaaIAttrs.begin(), fAttrs, 64, formats, &num);
	num = SkTMin(num, 64U);
	formatsToTry[0] = extensions.selectFormat(formats, num, dc, msaaSampleCount);
	}

	// Get a non-MSAA format
	int* format = -1 == formatsToTry[0] ? &formatsToTry[0] : &formatsToTry[1];
	unsigned int num;
	appendAttr(iAttrs, 0, 0);
	extensions.choosePixelFormat(dc, iAttrs.begin(), fAttrs, 1, format, &num);
	}

	static HGLRC create_gl_context(HDC dc, SkWGLExtensions extensions, SkWGLContextRequest contextType) {
	HDC prevDC = wglGetCurrentDC();
	HGLRC prevGLRC = wglGetCurrentContext();

	HGLRC glrc = nullptr;
	if (kGLES_SkWGLContextRequest == contextType) {
	if (!extensions.hasExtension(dc, "WGL_EXT_create_context_es2_profile")) {
	wglMakeCurrent(prevDC, prevGLRC);
	return nullptr;
	}
	static const int glesAttribs[] = {
	SK_WGL_CONTEXT_MAJOR_VERSION, 3,
	SK_WGL_CONTEXT_MINOR_VERSION, 0,
	SK_WGL_CONTEXT_PROFILE_MASK, SK_WGL_CONTEXT_ES2_PROFILE_BIT,
	0,
	};
	glrc = extensions.createContextAttribs(dc, nullptr, glesAttribs);
	if (nullptr == glrc) {
	wglMakeCurrent(prevDC, prevGLRC);
	return nullptr;
	}
	} else {
	if (kGLPreferCoreProfile_SkWGLContextRequest == contextType &&
	extensions.hasExtension(dc, "WGL_ARB_create_context")) {
	static const int kCoreGLVersions[] = {
	4, 3,
	4, 2,
	4, 1,
	4, 0,
	3, 3,
	3, 2,
	};
	int coreProfileAttribs[] = {
	SK_WGL_CONTEXT_MAJOR_VERSION, -1,
	SK_WGL_CONTEXT_MINOR_VERSION, -1,
	SK_WGL_CONTEXT_PROFILE_MASK, SK_WGL_CONTEXT_CORE_PROFILE_BIT,
	0,
	};
	for (int v = 0; v < SK_ARRAY_COUNT(kCoreGLVersions) / 2; ++v) {
	coreProfileAttribs[1] = kCoreGLVersions[2 * v];
	coreProfileAttribs[3] = kCoreGLVersions[2 * v + 1];
	glrc = extensions.createContextAttribs(dc, nullptr, coreProfileAttribs);
	if (glrc) {
	break;
	}
	}
	}
	}

	if (nullptr == glrc) {
	glrc = wglCreateContext(dc);
	}
	SkASSERT(glrc);

	wglMakeCurrent(prevDC, prevGLRC);

	// This might help make the context non-vsynced.
	if (extensions.hasExtension(dc, "WGL_EXT_swap_control")) {
	extensions.swapInterval(-1);
	}
	return glrc;
	}

	HGLRC SkCreateWGLContext(HDC dc, int msaaSampleCount, bool deepColor,
	SkWGLContextRequest contextType) {
	SkWGLExtensions extensions;
	if (!extensions.hasExtension(dc, "WGL_ARB_pixel_format")) {
	return nullptr;
	}

	BOOL set = FALSE;

	int pixelFormatsToTry[] = { -1, -1 };
	get_pixel_formats_to_try(dc, extensions, true, msaaSampleCount, deepColor, pixelFormatsToTry);
	for (int f = 0;
	!set && -1 != pixelFormatsToTry[f] && f < SK_ARRAY_COUNT(pixelFormatsToTry);
	++f) {
	PIXELFORMATDESCRIPTOR pfd;
	DescribePixelFormat(dc, pixelFormatsToTry[f], sizeof(pfd), &pfd);
	set = SetPixelFormat(dc, pixelFormatsToTry[f], &pfd);
	}

	if (!set) {
	return nullptr;
	}

	return create_gl_context(dc, extensions, contextType);}

	SkWGLPbufferContext* SkWGLPbufferContext::Create(HDC parentDC, int msaaSampleCount,
	SkWGLContextRequest contextType) {
	SkWGLExtensions extensions;
	if (!extensions.hasExtension(parentDC, "WGL_ARB_pixel_format") \|\|
	!extensions.hasExtension(parentDC, "WGL_ARB_pbuffer")) {
	return nullptr;
	}

	// try for single buffer first
	for (int dblBuffer = 0; dblBuffer < 2; ++dblBuffer) {
	int pixelFormatsToTry[] = { -1, -1 };
	get_pixel_formats_to_try(parentDC, extensions, (0 != dblBuffer), msaaSampleCount,
	false, pixelFormatsToTry);
	for (int f = 0; -1 != pixelFormatsToTry[f] && f < SK_ARRAY_COUNT(pixelFormatsToTry); ++f) {
	HPBUFFER pbuf = extensions.createPbuffer(parentDC, pixelFormatsToTry[f], 1, 1, nullptr);
	if (0 != pbuf) {
	HDC dc = extensions.getPbufferDC(pbuf);
	if (dc) {
	HGLRC glrc = create_gl_context(dc, extensions, contextType);
	if (glrc) {
	return new SkWGLPbufferContext(pbuf, dc, glrc);
	}
	extensions.releasePbufferDC(pbuf, dc);
	}
	extensions.destroyPbuffer(pbuf);
	}
	}
	}
	return nullptr;
	}

	SkWGLPbufferContext::~SkWGLPbufferContext() {
	SkASSERT(fExtensions.hasExtension(fDC, "WGL_ARB_pbuffer"));
	wglDeleteContext(fGLRC);
	fExtensions.releasePbufferDC(fPbuffer, fDC);
	fExtensions.destroyPbuffer(fPbuffer);
	}

	SkWGLPbufferContext::SkWGLPbufferContext(HPBUFFER pbuffer, HDC dc, HGLRC glrc)
	: fPbuffer(pbuffer)
	, fDC(dc)
	, fGLRC(glrc) {
	}

	#endif//defined(SK_BUILD_FOR_WIN32)