new file mode 100644
--- /dev/null
+++ b/src/th06/interpolator.rs
@@ -0,0 +1,77 @@
+//! Animation runner.
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub(crate) enum Formula {
+    Linear,
+    Power2,
+    InvertPower2,
+}
+
+impl Formula {
+    fn apply(&self, x: f32) -> f32 {
+        match self {
+            Formula::Linear => x,
+            Formula::Power2 => x * x,
+            Formula::InvertPower2 => 2. * x - x * x,
+        }
+    }
+}
+
+macro_rules! generate_interpolator {
+    ($name:ident, $n:tt) => {
+        #[derive(Debug, Clone)]
+        pub(crate) struct $name<T> {
+            start_values: [T; $n],
+            end_values: [T; $n],
+            start_frame: u16,
+            end_frame: u16,
+            formula: Formula,
+        }
+
+        impl<T> $name<T>
+        where f32: From<T>,
+              T: From<f32>,
+              T: std::ops::Sub<Output = T>,
+              T: std::ops::Add<Output = T>,
+              T: Copy,
+              T: Default,
+        {
+            pub fn new(start_values: [T; $n], start_frame: u16, end_values: [T; $n], end_frame: u16, formula: Formula) -> $name<T> {
+                $name {
+                    start_values,
+                    end_values,
+                    start_frame,
+                    end_frame,
+                    formula,
+                }
+            }
+
+            // XXX: Make it return [T; $n] instead, we don’t want to only do f32 here.
+            pub fn values(&self, frame: u16) -> [f32; $n] {
+                if frame + 1 >= self.end_frame {
+                    // XXX: skip the last interpolation step.
+                    // This bug is replicated from the original game.
+                    //self.start_frame = self.end_frame;
+                    //self.end_values
+                    let mut values: [f32; $n] = [Default::default(); $n];
+                    for (i, value) in self.end_values.iter().enumerate() {
+                        values[i] = f32::from(*value);
+                    }
+                    values
+                } else {
+                    let mut coeff = (frame - self.start_frame) as f32 / (self.end_frame - self.start_frame) as f32;
+                    coeff = self.formula.apply(coeff);
+                    let mut values: [f32; $n] = [Default::default(); $n];
+                    for (i, (start, end)) in self.start_values.iter().zip(&self.end_values).enumerate() {
+                        values[i] = f32::from(*start + T::from(coeff * f32::from(*end - *start)));
+                    }
+                    values
+                }
+            }
+        }
+    };
+}
+
+generate_interpolator!(Interpolator1, 1);
+generate_interpolator!(Interpolator2, 2);
+generate_interpolator!(Interpolator3, 3);