Added support for choosing the rendering gpu using wgl_nv_affinity

extension.

Added Native API call to get the device context.

docs/window.dox

@@ -188,6 +188,11 @@ used by the context.  This can be one of `GLFW_NO_RESET_NOTIFICATION` or
 `GLFW_LOSE_CONTEXT_ON_RESET`, or `GLFW_NO_ROBUSTNESS` to not request
 a robustness strategy.
 
+The `GLFW_AFFINITY_GPU` hint specifies which GPU should render OpenGL commands
+for the associated context. This uses the WGL_NV_gpu_affinity extension, and is
+only available on windows systems. The value corresponds with an index position
+returned from a call to wglEnumGpusNV(...). Note that if sharing context resources
+with another window, both windows must have the same affinity gpu mask.
 
 @subsection window_hints_values Supported and default values
 
@@ -218,6 +223,7 @@ a robustness strategy.
 | `GLFW_OPENGL_FORWARD_COMPAT` | `GL_FALSE`                | `GL_TRUE` or `GL_FALSE` |
 | `GLFW_OPENGL_DEBUG_CONTEXT`  | `GL_FALSE`                | `GL_TRUE` or `GL_FALSE` |
 | `GLFW_OPENGL_PROFILE`        | `GLFW_OPENGL_ANY_PROFILE` | `GLFW_OPENGL_ANY_PROFILE`, `GLFW_OPENGL_COMPAT_PROFILE` or `GLFW_OPENGL_CORE_PROFILE` |
+| `GLFW_AFFINITY_GPU`          | -1                        | 0 to maximum number of GPUs |
 
 
 @section window_close Window close flag

include/GLFW/glfw3.h

@@ -511,6 +511,7 @@ extern "C" {
 #define GLFW_SAMPLES                0x0002100D
 #define GLFW_SRGB_CAPABLE           0x0002100E
 #define GLFW_REFRESH_RATE           0x0002100F
+#define GLFW_AFFINITY_GPU           0x00021010
 
 #define GLFW_CLIENT_API             0x00022001
 #define GLFW_CONTEXT_VERSION_MAJOR  0x00022002

include/GLFW/glfw3native.h

@@ -115,6 +115,11 @@ GLFWAPI HWND glfwGetWin32Window(GLFWwindow* window);
  *  @ingroup native
  */
 GLFWAPI HGLRC glfwGetWGLContext(GLFWwindow* window);
+/*! @brief Returns the `HDC` of the specified window.
+ *  @return The `HDC` of the specified window.
+ *  @ingroup native
+ */
+GLFWAPI HDC glfwGetWGLDC(GLFWwindow* window);
 #endif
 
 #if defined(GLFW_EXPOSE_NATIVE_COCOA)

src/internal.h

@@ -299,6 +299,7 @@ struct _GLFWlibrary
         GLboolean   glDebug;
         int         glProfile;
         int         glRobustness;
+        int         gpu;
     } hints;
 
     double          cursorPosX, cursorPosY;

src/wgl_context.c

@@ -46,6 +46,9 @@ static void initWGLExtensions(_GLFWwindow* window)
     window->wgl.GetExtensionsStringARB = NULL;
     window->wgl.GetExtensionsStringEXT = NULL;
     window->wgl.CreateContextAttribsARB = NULL;
+	window->wgl.CreateAffinityDCNV = NULL;
+	window->wgl.DeleteDCNV = NULL;
+	window->wgl.EnumGpusNV = NULL;
 
     // This needs to include every extension used below except for
     // WGL_ARB_extensions_string and WGL_EXT_extensions_string
@@ -57,6 +60,7 @@ static void initWGLExtensions(_GLFWwindow* window)
     window->wgl.ARB_create_context_robustness = GL_FALSE;
     window->wgl.EXT_swap_control = GL_FALSE;
     window->wgl.ARB_pixel_format = GL_FALSE;
+	window->wgl.NV_gpu_affinity = GL_FALSE;
 
     window->wgl.GetExtensionsStringEXT = (PFNWGLGETEXTENSIONSSTRINGEXTPROC)
         wglGetProcAddress("wglGetExtensionsStringEXT");
@@ -119,6 +123,21 @@ static void initWGLExtensions(_GLFWwindow* window)
         if (window->wgl.GetPixelFormatAttribivARB)
             window->wgl.ARB_pixel_format = GL_TRUE;
     }
+
+	if (_glfwPlatformExtensionSupported("WGL_NV_gpu_affinity"))
+	{
+		window->wgl.EnumGpusNV = (PFNWGLENUMGPUSNVPROC)
+			wglGetProcAddress("wglEnumGpusNV");
+
+		window->wgl.CreateAffinityDCNV = (PFNWGLCREATEAFFINITYDCNVPROC)
+			wglGetProcAddress("wglCreateAffinityDCNV");
+
+		window->wgl.DeleteDCNV = (PFNWGLDELETEDCNVPROC)
+			wglGetProcAddress("wglDeleteDCNV");
+		
+		if (window->wgl.EnumGpusNV && window->wgl.CreateAffinityDCNV)
+			window->wgl.NV_gpu_affinity = GL_TRUE;
+	}
 }
 
 // Returns the specified attribute of the specified pixel format
@@ -358,7 +377,7 @@ int _glfwCreateContext(_GLFWwindow* window,
     if (wndconfig->share)
         share = wndconfig->share->wgl.context;
 
-    window->wgl.dc = GetDC(window->win32.handle);
+	window->wgl.dc = GetDC(window->win32.handle);
     if (!window->wgl.dc)
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
@@ -384,6 +403,30 @@ int _glfwCreateContext(_GLFWwindow* window,
         return GL_FALSE;
     }
 
+	// If the nvidia affinity extension is available and the gpu has been set through a hint, create an affinityDC bound to a specific gpu.
+	// We create the affinityDC and then make an affinity context using the
+	// affinityDC. Because we are doing onscreen rendering and the affinityDC isn't bound to a window (i.e. doesn't contain a framebuffer),
+	// we make the affinitycontext current with the normal dc that is bound to the window.
+	if (window->wgl.NV_gpu_affinity && _glfw.hints.gpu != -1)
+	{
+		HGPUNV gpuMask;
+		window->wgl.EnumGpusNV(_glfw.hints.gpu, &gpuMask);
+		window->wgl.affinityDC = window->wgl.CreateAffinityDCNV(&gpuMask);
+		if (!window->wgl.affinityDC)
+		{
+			_glfwInputError(GLFW_PLATFORM_ERROR,
+							"WGL: Failed to create NV Affinity DC for window");
+		}
+		else {
+			if (!SetPixelFormat(window->wgl.affinityDC, pixelFormat, &pfd))
+			{
+				_glfwInputError(GLFW_PLATFORM_ERROR,
+								"Win32: Failed to set selected pixel format for affinity DC");
+				return GL_FALSE;
+			}
+		}
+	}
+
     if (window->wgl.ARB_create_context)
     {
         int index = 0, mask = 0, flags = 0, strategy = 0;
@@ -437,9 +480,19 @@ int _glfwCreateContext(_GLFWwindow* window,
 
         setWGLattrib(0, 0);
 
-        window->wgl.context = window->wgl.CreateContextAttribsARB(window->wgl.dc,
+        if (window->wgl.affinityDC)
-                                                                  share,
+		{
-                                                                  attribs);
+			window->wgl.context = window->wgl.CreateContextAttribsARB(window->wgl.affinityDC,
+																	  share,
+																	  attribs);
+		}
+		else
+		{
+			window->wgl.context = window->wgl.CreateContextAttribsARB(window->wgl.dc,
+																	  share,
+																	  attribs);
+		}
+
         if (!window->wgl.context)
         {
             _glfwInputError(GLFW_VERSION_UNAVAILABLE,
@@ -449,7 +502,11 @@ int _glfwCreateContext(_GLFWwindow* window,
     }
     else
     {
-        window->wgl.context = wglCreateContext(window->wgl.dc);
+        if (window->wgl.affinityDC)
+			window->wgl.context = wglCreateContext(window->wgl.affinityDC);
+		else
+			window->wgl.context = wglCreateContext(window->wgl.dc);
+
         if (!window->wgl.context)
         {
             _glfwInputError(GLFW_PLATFORM_ERROR,
@@ -490,8 +547,14 @@ void _glfwDestroyContext(_GLFWwindow* window)
     if (window->wgl.dc)
     {
         ReleaseDC(window->win32.handle, window->wgl.dc);
-        window->wgl.dc = NULL;
+		window->wgl.dc = NULL;
     }
+
+	if (window->wgl.affinityDC)
+	{
+		window->wgl.DeleteDCNV(window->wgl.affinityDC);
+		window->wgl.affinityDC = NULL;
+	}
 }
 
 // Analyzes the specified context for possible recreation
@@ -570,6 +633,12 @@ int _glfwAnalyzeContext(const _GLFWwindow* window,
         }
     }
 
+	if (window->wgl.NV_gpu_affinity && _glfw.hints.gpu != -1)
+	{
+		// We have requested an nvidia affinity context with a specific gpu
+		required = GL_TRUE;
+	}
+
     if (required)
         return _GLFW_RECREATION_REQUIRED;
 
@@ -668,3 +737,9 @@ GLFWAPI HGLRC glfwGetWGLContext(GLFWwindow* handle)
     return window->wgl.context;
 }
 
+GLFWAPI HDC glfwGetWGLDC(GLFWwindow* handle)
+{
+	_GLFWwindow* window = (_GLFWwindow*) handle;
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+	return window->wgl.dc;
+}

src/wgl_platform.h

@@ -50,6 +50,7 @@ typedef struct _GLFWcontextWGL
 {
     // Platform specific window resources
     HDC       dc;              // Private GDI device context
+	HDC       affinityDC;      // gpu affinity device context
     HGLRC     context;         // Permanent rendering context
 
     // Platform specific extensions (context specific)
@@ -58,6 +59,9 @@ typedef struct _GLFWcontextWGL
     PFNWGLGETEXTENSIONSSTRINGEXTPROC    GetExtensionsStringEXT;
     PFNWGLGETEXTENSIONSSTRINGARBPROC    GetExtensionsStringARB;
     PFNWGLCREATECONTEXTATTRIBSARBPROC   CreateContextAttribsARB;
+	PFNWGLCREATEAFFINITYDCNVPROC		CreateAffinityDCNV;
+	PFNWGLDELETEDCNVPROC				DeleteDCNV;
+	PFNWGLENUMGPUSNVPROC				EnumGpusNV;
     GLboolean                           EXT_swap_control;
     GLboolean                           ARB_multisample;
     GLboolean                           ARB_framebuffer_sRGB;
@@ -66,6 +70,7 @@ typedef struct _GLFWcontextWGL
     GLboolean                           ARB_create_context_profile;
     GLboolean                           EXT_create_context_es2_profile;
     GLboolean                           ARB_create_context_robustness;
+	GLboolean							NV_gpu_affinity;
 } _GLFWcontextWGL;
 
 

src/window.c

@@ -284,6 +284,9 @@ void glfwDefaultWindowHints(void)
     _glfw.hints.alphaBits   = 8;
     _glfw.hints.depthBits   = 24;
     _glfw.hints.stencilBits = 8;
+
+	// Set the default gpu to -1.
+    _glfw.hints.gpu = -1;
 }
 
 GLFWAPI void glfwWindowHint(int target, int hint)
@@ -366,6 +369,9 @@ GLFWAPI void glfwWindowHint(int target, int hint)
             break;
         case GLFW_OPENGL_PROFILE:
             _glfw.hints.glProfile = hint;
+            break;
+		case GLFW_AFFINITY_GPU:
+            _glfw.hints.gpu = hint;
             break;
         default:
             _glfwInputError(GLFW_INVALID_ENUM, NULL);