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diff --git a/src/curvemap.cc b/src/curvemap.cc
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+++ b/src/curvemap.cc
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+/* -*- Mode: c++ -*- */
+/***************************************************************************
+ *            powermap.cc
+ *
+ *  Fri Apr 17 23:06:12 CEST 2020
+ *  Copyright 2020 André Nusser
+ *  andre.nusser@googlemail.com
+ ****************************************************************************/
+
+/*
+ *  This file is part of DrumGizmo.
+ *
+ *  DrumGizmo is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation; either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  DrumGizmo 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 Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with DrumGizmo; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA.
+ */
+#include "curvemap.h"
+
+#include <cassert>
+#include <cmath>
+
+namespace
+{
+
+using CurveValue = CurveMap::CurveValue;
+using CurveValuePair = CurveMap::CurveValuePair;
+
+CurveValue h00(CurveValue x)
+{
+	return (1 + 2 * x) * pow(1 - x, 2);
+}
+
+CurveValue h10(CurveValue x)
+{
+	return x * pow(1 - x, 2);
+}
+
+CurveValue h01(CurveValue x)
+{
+	return x * x * (3 - 2 * x);
+}
+
+CurveValue h11(CurveValue x)
+{
+	return x * x * (x - 1);
+}
+
+CurveValue computeValue(const CurveValue x, const CurveValuePair& P0, const CurveValuePair& P1,
+                        const CurveValue m0, const CurveValue m1)
+{
+	const auto x0 = P0.in;
+	const auto x1 = P1.in;
+	const auto y0 = P0.out;
+	const auto y1 = P1.out;
+	const auto dx = x1 - x0;
+	const auto x_prime = (x - x0)/dx;
+
+	return
+		h00(x_prime) * y0 +
+		h10(x_prime) * dx * m0 +
+		h01(x_prime) * y1 +
+		h11(x_prime) * dx * m1;
+}
+
+} // end anonymous namespace
+
+CurveMap::CurveMap()
+{
+	reset();
+}
+
+CurveValue CurveMap::map(CurveValue in)
+{
+	assert(in >= 0. && in <= 1.);
+	if (invert)
+	{
+		in = 1.0 - in;
+	}
+
+	if (spline_needs_update)
+	{
+		updateSpline();
+	}
+
+	CurveValue out;
+	if (in < fixed[0].in)
+	{
+		out = shelf ? fixed[0].out
+		            : computeValue(in, {0.,0.}, fixed[0], m[0], m[1]);
+	}
+	else if (in < fixed[1].in)
+	{
+		out = computeValue(in, fixed[0], fixed[1], m[1], m[2]);
+	}
+	else if (in < fixed[2].in)
+	{
+		out = computeValue(in, fixed[1], fixed[2], m[2], m[3]);
+	}
+	else
+	{
+		// in >= fixed[2].in
+		out = shelf ? fixed[2].out
+		            : computeValue(in, fixed[2], {1.,1.}, m[3], m[4]);
+	}
+
+	assert(out >= 0. && out <= 1.);
+	return out;
+}
+
+void CurveMap::reset()
+{
+	setFixed0({eps, eps});
+	setFixed1({.5, .5});
+	setFixed2({1 - eps, 1 - eps});
+	// FIXME: better false?
+	shelf = true;
+	invert = false;
+
+	updateSpline();
+}
+
+void CurveMap::setFixed0(CurveValuePair new_value)
+{
+	if (fixed[0] != new_value)
+	{
+		spline_needs_update = true;
+		fixed[0].in = clamp(new_value.in, eps, fixed[1].in - eps);
+		fixed[0].out = clamp(new_value.out, eps, fixed[1].out - eps);
+	}
+}
+
+void CurveMap::setFixed1(CurveValuePair new_value)
+{
+	if (fixed[1] != new_value)
+	{
+		spline_needs_update = true;
+		fixed[1].in = clamp(new_value.in, fixed[0].in + eps, fixed[2].in - eps);
+		fixed[1].out = clamp(new_value.out, fixed[0].out + eps, fixed[2].out - eps);
+	}
+}
+
+void CurveMap::setFixed2(CurveValuePair new_value)
+{
+	if (fixed[2] != new_value)
+	{
+		spline_needs_update = true;
+		fixed[2].in = clamp(new_value.in, fixed[1].in + eps, 1 - eps);
+		fixed[2].out = clamp(new_value.out, fixed[1].out + eps, 1 - eps);
+	}
+}
+
+void CurveMap::setInvert(bool enable)
+{
+	invert = enable;
+}
+
+void CurveMap::setShelf(bool enable)
+{
+	if (shelf != enable)
+	{
+		spline_needs_update = true;
+		this->shelf = enable;
+	}
+}
+
+CurveValuePair CurveMap::getFixed0() const
+{
+	return fixed[0];
+}
+
+CurveValuePair CurveMap::getFixed1() const
+{
+	return fixed[1];
+}
+
+CurveValuePair CurveMap::getFixed2() const
+{
+	return fixed[2];
+}
+
+bool CurveMap::getInvert() const {
+	return invert;
+}
+
+bool CurveMap::getShelf() const {
+	return shelf;
+}
+
+// This mostly followes the wikipedia article for monotone cubic splines:
+// https://en.wikipedia.org/wiki/Monotone_cubic_interpolation
+void CurveMap::updateSpline()
+{
+	assert(0. <= fixed[0].in && fixed[0].in < fixed[1].in &&
+	       fixed[1].in < fixed[2].in && fixed[2].in <= 1.);
+	assert(0. <= fixed[0].out && fixed[0].out <= fixed[1].out &&
+	       fixed[1].out <= fixed[2].out && fixed[2].out <= 1.);
+
+	CurveValues X = shelf ? CurveValues{fixed[0].in, fixed[1].in, fixed[2].in}
+	                 : CurveValues{0., fixed[0].in, fixed[1].in, fixed[2].in, 1.};
+	CurveValues Y = shelf ? CurveValues{fixed[0].out, fixed[1].out, fixed[2].out}
+	                 : CurveValues{0., fixed[0].out, fixed[1].out, fixed[2].out, 1.};
+
+	auto slopes = calcSlopes(X, Y);
+
+	if (shelf)
+	{
+		assert(slopes.size() == 3);
+		this->m[1] = slopes[0];
+		this->m[2] = slopes[1];
+		this->m[3] = slopes[2];
+	}
+	else
+	{
+		assert(slopes.size() == 5);
+		for (std::size_t i = 0; i < m.size(); ++i)
+		{
+			this->m[i] = slopes[i];
+		}
+	}
+
+	spline_needs_update = false;
+}
+
+// This follows the monotone cubic spline algorithm of Steffen, from:
+// "A Simple Method for Monotonic Interpolation in One Dimension"
+std::vector<float> CurveMap::calcSlopes(const CurveValues& X, const CurveValues& Y)
+{
+	CurveValues m(X.size());
+
+	CurveValues d(X.size() - 1);
+	CurveValues h(X.size() - 1);
+	for (std::size_t i = 0; i < d.size(); ++i)
+	{
+		h[i] = X[i + 1] - X[i];
+		d[i] = (Y[i + 1] - Y[i]) / h[i];
+	}
+
+	m.front() = d.front();
+	for (std::size_t i = 1; i < m.size() - 1; ++i)
+	{
+		m[i] = (d[i - 1] + d[i]) / 2.;
+	}
+	m.back() = d.back();
+
+	for (std::size_t i = 1; i < m.size() - 1; ++i)
+	{
+		const auto min_d = 2*std::min(d[i - 1], d[i]);
+		m[i] =
+			std::min<float>(min_d,
+			                (h[i] * d[i - 1] + h[i - 1] * d[i]) / (h[i - 1] + h[i]));
+	}
+
+	return m;
+}
+
+CurveValue CurveMap::clamp(CurveValue in, CurveValue min, CurveValue max) const
+{
+	return std::max(min, std::min(in, max));
+}
+
+bool CurveMap::operator==(const CurveMap& other) const
+{
+	return getFixed0() == other.getFixed0() &&
+	       getFixed1() == other.getFixed1() &&
+		   getFixed2() == other.getFixed2() &&
+		   getShelf() == other.getShelf() &&
+		   getInvert() == other.getInvert();
+}