From 8da0925d6d4696b050dc0862979beb391508f7ee Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@gmta.nl>
Date: Tue, 4 Jan 2022 15:01:25 +0100
Subject: [PATCH] AK: Add `mix`

---
 AK/StdLibExtras.h             |  7 +++++++
 Tests/AK/TestStdLibExtras.cpp | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/AK/StdLibExtras.h b/AK/StdLibExtras.h
index 844996cacf..2fcb8565b9 100644
--- a/AK/StdLibExtras.h
+++ b/AK/StdLibExtras.h
@@ -91,6 +91,12 @@ constexpr T clamp(const T& value, const IdentityType<T>& min, const IdentityType
     return value;
 }
 
+template<typename T, typename U>
+constexpr T mix(T const& v1, T const& v2, U const& interpolation)
+{
+    return v1 + (v2 - v1) * interpolation;
+}
+
 template<typename T, typename U>
 constexpr T ceil_div(T a, U b)
 {
@@ -167,6 +173,7 @@ using AK::exchange;
 using AK::is_constant_evaluated;
 using AK::max;
 using AK::min;
+using AK::mix;
 using AK::RawPtr;
 using AK::swap;
 using AK::to_underlying;
diff --git a/Tests/AK/TestStdLibExtras.cpp b/Tests/AK/TestStdLibExtras.cpp
index 6a371cfcac..0dc5113160 100644
--- a/Tests/AK/TestStdLibExtras.cpp
+++ b/Tests/AK/TestStdLibExtras.cpp
@@ -12,6 +12,20 @@
 #include <AK/Variant.h>
 #include <AK/Vector.h>
 
+TEST_CASE(mix)
+{
+    double a = 1.0;
+    double b = 3.0;
+
+    EXPECT_APPROXIMATE(mix(a, b, 0.0), 1.0);
+    EXPECT_APPROXIMATE(mix(a, b, 0.5), 2.0);
+    EXPECT_APPROXIMATE(mix(a, b, 1.0), 3.0);
+
+    EXPECT_APPROXIMATE(mix(b, a, 0.0), 3.0);
+    EXPECT_APPROXIMATE(mix(b, a, 0.5), 2.0);
+    EXPECT_APPROXIMATE(mix(b, a, 1.0), 1.0);
+}
+
 TEST_CASE(swap)
 {
     int i = 4;