3 files changed, 52 insertions, 0 deletions
diff --git a/src/interpolation.rs b/src/interpolation.rs
new file mode 100644
index 0000000..de6b6df
--- /dev/null
+++ b/src/interpolation.rs
@@ -0,0 +1,50 @@
+use std::ops::{Add, Mul, Sub};
+
+pub fn raw_lerp<T>(a: T, b: T, t: f64) -> T
+where
+  T: Copy + Add<Output = T> + Sub<Output = T> + Mul<f64, Output = T>,
+{
+  a + (b - a) * t
+}
+
+pub enum TimingFunction {
+  Lerp,
+}
+pub struct KeyFrame<ValueType> {
+  // We could make a TimeType generic (I initially did), however it's safe to assume we use a 64-bit float for this
+  pub time: f64,
+  pub val: ValueType,
+}
+impl<ValueType> KeyFrame<ValueType> {
+  pub fn new(time: f64, val: ValueType) -> KeyFrame<ValueType> {
+    KeyFrame { time, val }
+  }
+}
+impl<
+    ValueType: PartialOrd
+      + Copy
+      + Add<Output = ValueType>
+      + Sub<Output = ValueType>
+      + Mul<f64, Output = ValueType>,
+  > KeyFrame<ValueType>
+{
+  /** Simply passes the data to the timing function involved. Does not do bounding. */
+  pub fn raw_value_at(
+    from: &KeyFrame<ValueType>,
+    to: &KeyFrame<ValueType>,
+    time: f64,
+    timing_function: TimingFunction,
+  ) -> ValueType {
+    // Order them so `from` is always the lower bound
+    let (from, to) = if from.time < to.time {
+      (from, to)
+    } else {
+      (to, from)
+    };
+    let length = to.time - from.time;
+    let position = (time - from.time) / length;
+    match timing_function {
+      TimingFunction::Lerp => raw_lerp(from.val, to.val, position),
+    }
+  }
+}
diff --git a/src/main.rs b/src/main.rs
index 5a653cd..f9c52f9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,6 +2,7 @@ extern crate sdl2;
 
 mod font;
 pub mod generated;
+mod interpolation;
 mod render;
 
 use std::time::{Duration, SystemTime};
diff --git a/src/render.rs b/src/render.rs
index ab9e48e..c4d207f 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -1,5 +1,6 @@
 use crate::font::BakedFont;
 use crate::generated::fonts::{FONT_CHERRY_BOMB_ONE, FONT_GALMURI};
+use crate::interpolation::KeyFrame;
 use sdl2::pixels::{Color, PixelFormatEnum};
 use sdl2::rect::Rect;
 use sdl2::render::{Canvas, Texture, TextureCreator};