Merged PR 167: Add Flex and fix bugs (read desc)

Note: The branch name does not fit the new features.

- Implement Flex with simplex
- Enable rigid body by default (removed IsRigidBody property) <=== possibly a bad idea
- Sort children in add and update properties
- Implement MaxWidth
- Add more docs

Fixes :
- .env.production url
- Symbols: not blocking the linked container when the parent is moving

src/utils/itertools.ts

@@ -14,7 +14,7 @@ export function * MakeIterator(root: IContainerModel): Generator<IContainerModel
     for (let i = container.children.length - 1; i >= 0; i--) {
       const child = container.children[i];
       if (visited.has(child)) {
-        return;
+        continue;
       }
       visited.add(child);
       queue.push(child);
@@ -71,9 +71,20 @@ export function getDepth(parent: IContainerModel): number {
  * @returns The absolute position of the container
  */
 export function getAbsolutePosition(container: IContainerModel): [number, number] {
-  let x = container.properties.x;
-  let y = container.properties.y;
-  let current = container.parent;
+  const x = container.properties.x;
+  const y = container.properties.y;
+  return cancelParentTransform(container.parent, x, y);
+}
+
+/**
+ * Cancel the hierarchic transformations to the given x, y
+ * @param parent Parent of the container to remove its transform
+ * @param x value to be restored
+ * @param y value to be restored
+ * @returns x and y such that the transformations of the parent are cancelled
+ */
+export function cancelParentTransform(parent: IContainerModel | null, x: number, y: number): [number, number] {
+  let current = parent;
   while (current != null) {
     x += current.properties.x;
     y += current.properties.y;
@@ -82,6 +93,23 @@ export function getAbsolutePosition(container: IContainerModel): [number, number
   return [x, y];
 }
 
+/**
+ * Cancel the hierarchic transformations to the given x, y
+ * @param parent Parent of the container to remove its transform
+ * @param x value to be restored
+ * @param y value to be restored
+ * @returns x and y such that the transformations of the parent are cancelled
+ */
+export function applyParentTransform(parent: IContainerModel | null, x: number, y: number): [number, number] {
+  let current = parent;
+  while (current != null) {
+    x -= current.properties.x;
+    y -= current.properties.y;
+    current = current.parent;
+  }
+  return [x, y];
+}
+
 export function findContainerById(root: IContainerModel, id: string): IContainerModel | undefined {
   const it = MakeIterator(root);
   for (const container of it) {
@@ -91,3 +119,20 @@ export function findContainerById(root: IContainerModel, id: string): IContainer
   }
   return undefined;
 }
+
+export interface IPair<T> {
+  cur: T
+  next: T
+}
+
+export function * pairwise<T>(arr: T[]): Generator<IPair<T>, void, unknown> {
+  for (let i = 0; i < arr.length - 1; i++) {
+    yield { cur: arr[i], next: arr[i + 1] };
+  }
+}
+
+export function * reversePairwise<T>(arr: T[]): Generator<IPair<T>, void, unknown> {
+  for (let i = arr.length - 1; i > 0; i--) {
+    yield { cur: arr[i], next: arr[i - 1] };
+  }
+}