Add lerp and inverseLerp helper functions

Return-To-The-Roots · Sep 18, 2022 · 793ef1b · 793ef1b
1 parent 64185ca
commit 793ef1b
Show file tree

Hide file tree

Showing 2 changed files with 36 additions and 1 deletion.
diff --git a/libs/common/include/helpers/mathFuncs.h b/libs/common/include/helpers/mathFuncs.h
@@ -50,7 +50,7 @@ constexpr U clamp(T val, U min, U max) noexcept
     // Here all values are positive or have the same signedness
     return static_cast<U>(clamp(static_cast<Common>(val), static_cast<Common>(min), static_cast<Common>(max)));
 }
-// Linear interpolation between [startVal, endVal]. Difference between those 2 and elapsedTime should be smallish
+/// Linear interpolation between [startVal, endVal]. Difference between those 2 and elapsedTime should be smallish
 template<typename T, typename U, typename V>
 constexpr T interpolate(const T startVal, const T endVal, const U elapsedTime, const V duration) noexcept
 {
@@ -66,4 +66,17 @@ constexpr T interpolate(const T startVal, const T endVal, const U elapsedTime, c
     else // Special case for unsigned values
         return static_cast<T>(startVal - ((startVal - endVal) * elapsedTime) / duration);
 }
+
+/// Linear interpolation, similar to C++20's std::lerp()
+constexpr float lerp(const float startVal, const float endVal, const float ratio) noexcept
+{
+    return startVal + ratio * (endVal - startVal);
+}
+
+/// Inverse function to lerp(): Returns the ratio of value in [startVal, endVal]
+template<typename T>
+constexpr T inverseLerp(const T startVal, const T endVal, const T value) noexcept
+{
+    return (value - startVal) / (endVal - startVal);
+}
 } // namespace helpers
diff --git a/tests/common/testMathHelpers.cpp b/tests/common/testMathHelpers.cpp
@@ -188,4 +188,26 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(Interpolate, T, TimeTypes)
     }
 }
 
+BOOST_AUTO_TEST_CASE(Lerp)
+{
+    const auto startVal = 5.0f;
+    const auto endVal = 10.0f;
+    BOOST_TEST(helpers::lerp(startVal, endVal, .0f) == startVal);
+    BOOST_TEST(helpers::lerp(startVal, endVal, 1.0f) == endVal);
+    BOOST_TEST(helpers::lerp(startVal, endVal, .5f) == 7.5f);
+    BOOST_TEST(helpers::lerp(startVal, endVal, 2.0f) == 15.0f);
+    BOOST_TEST(helpers::lerp(startVal, endVal, -.5f) == 2.5f);
+}
+
+BOOST_AUTO_TEST_CASE(InverseLerp)
+{
+    const auto startVal = 5.0f;
+    const auto endVal = 10.0f;
+    BOOST_TEST(helpers::inverseLerp(startVal, endVal, startVal) == .0f);
+    BOOST_TEST(helpers::inverseLerp(startVal, endVal, endVal) == 1.0f);
+    BOOST_TEST(helpers::inverseLerp(startVal, endVal, 7.5f) == .5f);
+    BOOST_TEST(helpers::inverseLerp(startVal, endVal, 15.0f) == 2.0f);
+    BOOST_TEST(helpers::inverseLerp(startVal, endVal, 2.5f) == -.5f);
+}
+
 BOOST_AUTO_TEST_SUITE_END()