Version 0.9

Added: Filter type "IIR", which allows to specify a user-defined IIR filter of arbitrary order with custom coefficients.
Improved: For playback devices, the APO is now installed both as GFX (post-mix) and LFX (pre-mix) APO. Normally the filtering happens in GFX, but the command "Stage" allows to select LFX to apply effects based on the number of input channels.
Added: Expression language. The commands "If", "ElseIf", "Else", "EndIf", "Eval" and inline expressions allow to change the filter behaviour based on runtime conditions.
Added: Command "Copy", which copies audio data between channels.
Added: Command "Delay", which delays the audio on the currently selected channels.
Improved: Configuration files are now locked exclusively for writing while reading them.
Improved: There is now a transition (10 ms) from old to new configuration after loading.
Improved: Substantial internal restructuring to improve extensibility and maintainability. Filtering commands now work exactly in the order they were specified.
Fixed: When the microphone input was in stereo but the application requested a mono stream, the audio was heavily distorted.
Fixed: The sine sweep generated by the Benchmark application had floating-point precision issues leading to severe artifacts when certain filters were applied.

filters/ExpressionFilterFactory.cpp

@@ -0,0 +1,152 @@
+/*
+	This file is part of EqualizerAPO, a system-wide equalizer.
+	Copyright (C) 2014  Jonas Thedering
+
+	This program is free software; you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation; either version 2 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License along
+	with this program; if not, write to the Free Software Foundation, Inc.,
+	51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include <sstream>
+
+#include "helpers/LogHelper.h"
+#include "helpers/StringHelper.h"
+#include "parser/RegexFunctions.h"
+#include "parser/RegistryFunctions.h"
+#include "parser/StringOperators.h"
+#include "FilterEngine.h"
+#include "ExpressionFilterFactory.h"
+
+using namespace std;
+using namespace mup;
+
+void ExpressionFilterFactory::initialize(FilterEngine* engine)
+{
+	parser = engine->getParser();
+	parser->DefineConst(L"inputChannelCount", (int)engine->getInputChannelCount());
+	parser->DefineConst(L"outputChannelCount", (int)engine->getOutputChannelCount());
+	parser->DefineConst(L"sampleRate", engine->getSampleRate());
+
+	parser->DefineFun(new ReadRegStringFunction(engine));
+	parser->DefineFun(new ReadRegDWORDFunction(engine));
+	parser->DefineFun(new RegexSearchFunction());
+	parser->DefineFun(new RegexReplaceFunction());
+
+	parser->RemoveOprt(L"+");
+	parser->DefineOprt(new AddOperator());
+}
+
+vector<IFilter*> ExpressionFilterFactory::createFilter(const wstring& configPath, wstring& command, wstring& parameters)
+{
+	if(command.length() > 0 && command[0] == L'#')
+		return vector<IFilter*>();
+
+	bool inExpression = false;
+	bool lastWasBackslash = false;
+
+	wstring output;
+	wstring expression;
+	for(unsigned i=0; i<parameters.size(); i++)
+	{
+		wchar_t c = parameters[i];
+		if(c == L'`')
+		{
+			if(!inExpression)
+			{
+				if(lastWasBackslash)
+				{
+					output += c;
+				}
+				else
+				{
+					inExpression = true;
+				}
+			}
+			else
+			{
+				if(lastWasBackslash)
+				{
+					expression += c;
+				}
+				else
+				{
+					inExpression = false;
+					try
+					{
+						parser->SetExpr(expression);
+						Value result = parser->Eval();
+						wstring resultString;
+						if(result.GetType() == L's')
+							resultString = result.GetString();
+						else
+							resultString = result.ToString().c_str();
+						output += resultString;
+						TraceF(L"Inline expression %s evaluated to %s", expression.c_str(), resultString.c_str());
+					}
+					catch(ParserError e)
+					{
+						LogF(L"Error while evaluating inline expression %s: %s", expression.c_str(), e.GetMsg().c_str());
+					}
+					expression.clear();
+				}
+			}
+			lastWasBackslash = false;
+		}
+		else if(c == L'\\')
+		{
+			if(i >= parameters.size()-1 || parameters[i+1] != L'`')
+			{
+				if(inExpression)
+					expression += c;
+				else
+					output += c;
+			}
+			lastWasBackslash = true;
+		}
+		else
+		{
+			if(inExpression)
+				expression += c;
+			else
+				output += c;
+			lastWasBackslash = false;
+		}
+	}
+
+	parameters = output;
+
+	if(command == L"Eval")
+	{
+		try
+		{
+			expression = StringHelper::trim(parameters);
+			parser->SetExpr(expression);
+			Value result = parser->Eval();
+			wstring resultString;
+			if(result.GetType() == L's')
+				resultString = result.GetString();
+			else
+				resultString = result.ToString().c_str();
+			TraceF(L"Expression %s evaluated to %s", expression.c_str(), resultString.c_str());
+		}
+		catch(ParserError e)
+		{
+			LogF(L"Error while evaluating expression %s: %s", expression.c_str(), e.GetMsg().c_str());
+		}
+
+		// command has been handled
+		command = L"";
+	}
+
+	return vector<IFilter*>();
+}