move some more stuff around

src/util/svg_helper.ts

@@ -0,0 +1,30 @@
+import { Rect2D } from "./geometry";
+
+// author: ChatGPT
+export function getBBoxInSvgCoords(el: SVGGraphicsElement, svg: SVGSVGElement): Rect2D {
+  const b = el.getBBox();
+  const m = el.getCTM()!;
+  const toSvg = (x: number, y: number) => {
+    const p = svg.createSVGPoint();
+    p.x = x; p.y = y;
+    return p.matrixTransform(m);
+  };
+  const pts = [
+    toSvg(b.x, b.y),
+    toSvg(b.x + b.width, b.y),
+    toSvg(b.x, b.y + b.height),
+    toSvg(b.x + b.width, b.y + b.height)
+  ];
+  const xs = pts.map(p => p.x);
+  const ys = pts.map(p => p.y);
+  return {
+    topLeft: {
+      x: Math.min(...xs),
+      y: Math.min(...ys),
+    },
+    size: {
+      x: Math.max(...xs) - Math.min(...xs),
+      y: Math.max(...ys) - Math.min(...ys),
+    },
+  };
+}