From 37e9626b240883567c2fb35f82f852337aa552bd Mon Sep 17 00:00:00 2001
From: annieversary <annnnnie@protonmail.com>
Date: Thu, 16 Sep 2021 15:26:41 +0200
Subject: [PATCH] [utils] add various crossfading things

---
 crates/utils/src/crossfade.rs | 30 ++++++++++++++++++++++++++++++
 crates/utils/src/lib.rs       |  1 +
 2 files changed, 31 insertions(+)
 create mode 100644 crates/utils/src/crossfade.rs

diff --git a/crates/utils/src/crossfade.rs b/crates/utils/src/crossfade.rs
new file mode 100644
index 0000000..fe41fc7
--- /dev/null
+++ b/crates/utils/src/crossfade.rs
@@ -0,0 +1,30 @@
+/// Linear crossfade
+/// x is the crossfading param, [0, 1]
+/// Returns (fade_in, fade_out)
+pub fn lin_crossfade(x: f32) -> (f32, f32) {
+    (x, 1.0 - x)
+}
+
+// next two are from https://signalsmith-audio.co.uk/writing/2021/cheap-energy-crossfade/
+
+/// Amplitude preserving crossfade
+/// x is the crossfading param, [0, 1]
+/// Returns (fade_in, fade_out)
+pub fn ap_crossfade(x: f32) -> (f32, f32) {
+    let fin = x * x * (3.0 - 2.0 * x);
+
+    (fin, 1.0 - fin)
+}
+
+/// Energy preserving crossfade
+/// x is the crossfading param, [0, 1]
+/// Returns (fade_in, fade_out)
+pub fn ep_crossfade(x: f32) -> (f32, f32) {
+    let x2 = 1.0 - x;
+    let a = x * x2;
+    let b = a * (1.0 + 1.4186 * a);
+    let c = b + x;
+    let d = b + x2;
+
+    (c * c, d * d)
+}
diff --git a/crates/utils/src/lib.rs b/crates/utils/src/lib.rs
index ca2b3c2..adbb2ee 100644
--- a/crates/utils/src/lib.rs
+++ b/crates/utils/src/lib.rs
@@ -1,4 +1,5 @@
 pub mod buffers;
+pub mod crossfade;
 pub mod delay;
 pub mod envelope;
 pub mod logs;