Add transform axis mapping functionality

src/viewport-three/transform-axis-mapping.ts

@@ -0,0 +1,40 @@
+import { Euler, Quaternion, Vector3 } from "three";
+
+import type { TransformAxis } from "../core/transform-session";
+import type { Vec3 } from "../core/vector";
+
+function axisVector(axis: TransformAxis): Vector3 {
+  switch (axis) {
+    case "x":
+      return new Vector3(1, 0, 0);
+    case "y":
+      return new Vector3(0, 1, 0);
+    case "z":
+      return new Vector3(0, 0, 1);
+  }
+}
+
+export function resolveDominantLocalAxisForWorldAxis(
+  rotationDegrees: Vec3,
+  worldAxis: TransformAxis
+): TransformAxis {
+  const orientation = new Quaternion().setFromEuler(
+    new Euler(
+      (rotationDegrees.x * Math.PI) / 180,
+      (rotationDegrees.y * Math.PI) / 180,
+      (rotationDegrees.z * Math.PI) / 180,
+      "XYZ"
+    )
+  );
+  const localAxis = axisVector(worldAxis)
+    .applyQuaternion(orientation.invert())
+    .normalize();
+  const axisWeights: Array<[TransformAxis, number]> = [
+    ["x", Math.abs(localAxis.x)],
+    ["y", Math.abs(localAxis.y)],
+    ["z", Math.abs(localAxis.z)]
+  ];
+
+  axisWeights.sort((left, right) => right[1] - left[1]);
+  return axisWeights[0]?.[0] ?? worldAxis;
+}