From 12b639970fc3ce08eada69d315470735fc23ef5f Mon Sep 17 00:00:00 2001
From: Jarek Kobus <jaroslaw.kobus@qt.io>
Date: Mon, 28 Nov 2022 11:28:49 +0100
Subject: [PATCH] MathUtils: Add exponential interpolation

Change-Id: I58bb26a6e921cbd1f5532bddcd6a6700ff80b94f
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
---
 src/libs/utils/mathutils.cpp                 | 25 +++++++++++++++---
 src/libs/utils/mathutils.h                   |  3 ++-
 tests/auto/utils/mathutils/tst_mathutils.cpp | 27 ++++++++++++++++++++
 3 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/src/libs/utils/mathutils.cpp b/src/libs/utils/mathutils.cpp
index d9e18b18a33..f1bdc5999c8 100644
--- a/src/libs/utils/mathutils.cpp
+++ b/src/libs/utils/mathutils.cpp
@@ -39,9 +39,26 @@ int interpolateTangential(int x, int xHalfLife, int y1, int y2)
         return y1;
     if (y1 == y2)
         return y1;
-    const double mapped = atan2(double(x), double(xHalfLife));
-    const double progress = y1 + (y2 - y1) * mapped * 2 / M_PI;
-    return qRound(progress);
+    const double angle = atan2((double)x, (double)xHalfLife);
+    const double result = y1 + (y2 - y1) * angle * 2 / M_PI;
+    return qRound(result);
 }
 
-} // namespace Utils::Math
+/*!
+    Exponential interpolation:
+    For x = 0 it returns y1.
+    For x = xHalfLife it returns 50 % of the distance between y1 and y2.
+    For x = infinity it returns y2.
+*/
+int interpolateExponential(int x, int xHalfLife, int y1, int y2)
+{
+    if (x == 0)
+        return y1;
+    if (y1 == y2)
+        return y1;
+    const double exponent = pow(0.5, (double)x / xHalfLife);
+    const double result = y1 + (y2 - y1) * (1.0 - exponent);
+    return qRound(result);
+}
+
+} // namespace Utils::MathUtils
diff --git a/src/libs/utils/mathutils.h b/src/libs/utils/mathutils.h
index 8a9af9e4e64..21f66ff5813 100644
--- a/src/libs/utils/mathutils.h
+++ b/src/libs/utils/mathutils.h
@@ -9,5 +9,6 @@ namespace Utils::MathUtils {
 
 QTCREATOR_UTILS_EXPORT int interpolateLinear(int x, int x1, int x2, int y1, int y2);
 QTCREATOR_UTILS_EXPORT int interpolateTangential(int x, int xHalfLife, int y1, int y2);
+QTCREATOR_UTILS_EXPORT int interpolateExponential(int x, int xHalfLife, int y1, int y2);
 
-} // namespace Utils::Math
+} // namespace Utils::MathUtils
diff --git a/tests/auto/utils/mathutils/tst_mathutils.cpp b/tests/auto/utils/mathutils/tst_mathutils.cpp
index 30d2d8d6c59..a585868d994 100644
--- a/tests/auto/utils/mathutils/tst_mathutils.cpp
+++ b/tests/auto/utils/mathutils/tst_mathutils.cpp
@@ -16,6 +16,8 @@ private slots:
     void interpolateLinear();
     void interpolateTangential_data();
     void interpolateTangential();
+    void interpolateExponential_data();
+    void interpolateExponential();
 };
 
 void tst_MathUtils::interpolateLinear_data()
@@ -72,6 +74,31 @@ void tst_MathUtils::interpolateTangential()
     QCOMPARE(y, result);
 }
 
+void tst_MathUtils::interpolateExponential_data()
+{
+    QTest::addColumn<int>("x");
+    QTest::addColumn<int>("xHalfLife");
+    QTest::addColumn<int>("y1");
+    QTest::addColumn<int>("y2");
+    QTest::addColumn<int>("result");
+
+    QTest::newRow("zero") << 0 << 8 << 10 << 20 << 10;
+    QTest::newRow("halfLife") << 8 << 8 << 10 << 20 << 15;
+    QTest::newRow("approxInfinity") << 1000 << 8 << 10 << 20 << 20;
+}
+
+void tst_MathUtils::interpolateExponential()
+{
+    QFETCH(int, x);
+    QFETCH(int, xHalfLife);
+    QFETCH(int, y1);
+    QFETCH(int, y2);
+    QFETCH(int, result);
+
+    const int y = MathUtils::interpolateExponential(x, xHalfLife, y1, y2);
+    QCOMPARE(y, result);
+}
+
 QTEST_GUILESS_MAIN(tst_MathUtils)
 
 #include "tst_mathutils.moc"