Refactor (#862)

* Initial factoring out of parts of the LayerUI component

2360 → 2224 LOC

* Create a Section component

* Break up src/index.tsx

* Refactor actions to reduce duplication, fix CSS

Also consolidate icons

* Move scene/data.ts to its own directory

* Fix accidental reverts, banish further single-character variables

* ACTIVE_ELEM_COLOR → ACTIVE_ELEMENT_COLOR

* Further refactoring the icons file

* Log all errors

* Pointer Event polyfill to make the tests work

* add test hooks & fix tests

Co-authored-by: dwelle <luzar.david@gmail.com>

src/scene/scroll.ts

@@ -0,0 +1,21 @@
+import { FlooredNumber } from "../types";
+import { ExcalidrawElement } from "../element/types";
+import { getCommonBounds } from "../element";
+
+export function normalizeScroll(pos: number) {
+  return Math.floor(pos) as FlooredNumber;
+}
+
+export function calculateScrollCenter(
+  elements: readonly ExcalidrawElement[],
+): { scrollX: FlooredNumber; scrollY: FlooredNumber } {
+  const [x1, y1, x2, y2] = getCommonBounds(elements);
+
+  const centerX = (x1 + x2) / 2;
+  const centerY = (y1 + y2) / 2;
+
+  return {
+    scrollX: normalizeScroll(window.innerWidth / 2 - centerX),
+    scrollY: normalizeScroll(window.innerHeight / 2 - centerY),
+  };
+}