wGL: Allow OpenGL debugging

This introduces a new command line parameter "--debug-opengl", which
will create special debug OpenGL contexts and attach a callback that the
driver will invoke when it detects a problem. The callback will then
write the error message to the logfile, and break into the debugger if
one is attached.
Currently only works on Windows.

src/config/C4Config.h

@@ -116,6 +116,7 @@ public:
 	int32_t NoOffscreenBlits; // if set, all blits to non-primary-surfaces are emulated
 	int32_t MultiSampling; // multisampling samples
 	int32_t AutoFrameSkip; // if true, gfx frames are skipped when they would slow down the game
+	int32_t DebugOpenGL; // if true, enables OpenGL debugging
 
 	void CompileFunc(StdCompiler *pComp);
 };

src/game/C4Application.cpp

@@ -259,6 +259,8 @@ void C4Application::ParseCommandLine(int argc, char * argv[])
 			{"record", no_argument, 0, 'r'},
 
 			{"lobby", required_argument, 0, 'l'},
+
+			{"debug-opengl", no_argument, &Config.Graphics.DebugOpenGL, 1},
 			{0, 0, 0, 0}
 		};
 		int option_index = 0;

src/graphics/C4DrawGL.cpp

@@ -36,6 +36,61 @@
 #include <stdio.h>
 #include <math.h>
 
+namespace
+{
+	const char *MsgSourceToStr(GLenum source)
+	{
+		switch (source)
+		{
+		case GL_DEBUG_SOURCE_API_ARB: return "API";
+		case GL_DEBUG_SOURCE_WINDOW_SYSTEM_ARB: return "window system";
+		case GL_DEBUG_SOURCE_SHADER_COMPILER_ARB: return "shader compiler";
+		case GL_DEBUG_SOURCE_THIRD_PARTY_ARB: return "third party";
+		case GL_DEBUG_SOURCE_APPLICATION_ARB: return "application";
+		case GL_DEBUG_SOURCE_OTHER_ARB: return "other";
+		default: return "<unknown>";
+		}
+	}
+
+	const char *MsgTypeToStr(GLenum type)
+	{
+		switch (type)
+		{
+		case GL_DEBUG_TYPE_ERROR_ARB: return "error";
+		case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR_ARB: return "deprecation warning";
+		case GL_DEBUG_TYPE_UNDEFINED_BEHAVIOR_ARB: return "undefined behavior warning";
+		case GL_DEBUG_TYPE_PORTABILITY_ARB: return "portability warning";
+		case GL_DEBUG_TYPE_PERFORMANCE_ARB: return "performance warning";
+		case GL_DEBUG_TYPE_OTHER_ARB: return "other message";
+		default: return "unknown message";
+		}
+	}
+
+	const char *MsgSeverityToStr(GLenum severity)
+	{
+		switch (severity)
+		{
+		case GL_DEBUG_SEVERITY_HIGH_ARB: return "high";
+		case GL_DEBUG_SEVERITY_MEDIUM_ARB: return "medium";
+		case GL_DEBUG_SEVERITY_LOW_ARB: return "low";
+		default: return "<unknown>";
+		}
+	}
+
+	void APIENTRY OpenGLDebugProc(GLenum source, GLenum type, GLuint id, GLenum severity, GLsizei length, const char* message, const void* userParam)
+	{
+		const char *msg_source = MsgSourceToStr(source);
+		const char *msg_type = MsgTypeToStr(type);
+		const char *msg_severity = MsgSeverityToStr(severity);
+
+		DebugLogF("  gl: %s severity %s %s: %s", msg_severity, msg_source, msg_type, message);
+#ifdef USE_WIN32_WINDOWS
+		if (IsDebuggerPresent() && severity == GL_DEBUG_SEVERITY_HIGH_ARB)
+			BREAKPOINT_HERE;
+#endif
+	}
+}
+
 CStdGL::CStdGL():
 		pMainCtx(0)
 {
@@ -153,6 +208,11 @@ CStdGLCtx *CStdGL::CreateContext(C4Window * pWindow, C4AbstractApp *pApp)
 	bool first_ctx = !pMainCtx;
 	if (first_ctx) pMainCtx = pCtx;
 	bool success = pCtx->Init(pWindow, pApp);
+	if (Config.Graphics.DebugOpenGL && glDebugMessageCallbackARB)
+	{
+		glDebugMessageCallbackARB(&OpenGLDebugProc, nullptr);
+		glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
+	}
 	// First context: Log some information about hardware/drivers
 	// Must log after context creation to get valid results
 	if (first_ctx)
@@ -186,6 +246,11 @@ CStdGLCtx *CStdGL::CreateContext(HWND hWindow, C4AbstractApp *pApp)
 	{
 		delete pCtx; Error("  gl: Error creating secondary context!"); return NULL;
 	}
+	if (Config.Graphics.DebugOpenGL && glDebugMessageCallbackARB)
+	{
+		glDebugMessageCallbackARB(&OpenGLDebugProc, nullptr);
+		glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
+	}
 	if (!pMainCtx)
 	{
 		pMainCtx = pCtx;

src/graphics/C4DrawGLCtx.cpp

@@ -306,7 +306,20 @@ bool CStdGLCtx::Init(C4Window * pWindow, C4AbstractApp *pApp, HWND hWindow)
 			else
 			{
 				// create context
-				hrc = wglCreateContext(hDC);
+				if (Config.Graphics.DebugOpenGL && wglCreateContextAttribsARB)
+				{
+					const int attribs[] = {
+						WGL_CONTEXT_FLAGS_ARB, WGL_CONTEXT_DEBUG_BIT_ARB,
+						0
+					};
+					DebugLog("  gl: Creating debug context.");
+					hrc = wglCreateContextAttribsARB(hDC, 0, attribs);
+				}
+				else
+				{
+					hrc = wglCreateContext(hDC);
+				}
+
 				if(!hrc)
 				{
 					pGL->Error("  gl: Error creating gl context");