dirty but the initial concept is working

src/VisualEditor/VisualEditor.css

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+.svgCanvas {
+  cursor: crosshair;
+}
+
+svg > text {
+  user-select: none;
+}
+
+.selecting {
+  fill: rgba(0, 0, 255, 0.2);
+  stroke-width: 1px;
+  stroke:black;
+  stroke-dasharray: 7 6;
+}
+
+.rountangle {
+  fill: rgba(255, 255, 255, 255);
+  /* fill: none; */
+  stroke: black;
+  stroke-width: 2px;
+}
+
+.rountangle:hover {
+  /* fill: lightgrey; */
+  /* stroke-width: 4px; */
+  cursor: grab;
+}
+
+.rountangle.dragging {
+  /* fill: lightgrey; */
+  /* stroke-width: 4px; */
+  cursor: grabbing;
+}
+
+/* .rountangle.selected {
+  fill: rgba(0, 0, 255, 0.2);
+  stroke: blue;
+  stroke-width: 4px;
+} */
+
+.lineHelper {
+  stroke: rgba(0, 0, 0, 0);
+  stroke-width: 16px;
+}
+.lineHelper:hover {
+  stroke: rgba(0, 255, 0, 0.2);
+  cursor: grab;
+}
+
+.circleHelper {
+  fill: rgba(0, 0, 0, 0);
+}
+.circleHelper:hover {
+  fill: rgba(0, 255, 0, 0.2);
+  cursor: grab;
+}
+
+.rountangle.or {
+  stroke-dasharray: 7 6;
+}
+
+.arrow {
+  stroke: black;
+  stroke-width: 2px;
+}
+
+/* .arrow.selected {
+  stroke: blue;
+  stroke-width: 4px;
+} */
+
+
+#arrowEnd {
+  fill: context-stroke;
+}
+
+.arrow:hover {
+  cursor: grab;
+}
+
+
+
+
+.selected {
+  fill: rgba(0, 0, 255, 0.2);
+  /* stroke-dasharray: 7 6; */
+  stroke: blue;
+  stroke-width: 4px;
+}

src/VisualEditor/VisualEditor.tsx

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+import { MouseEventHandler, useEffect, useRef, useState } from "react";
+import { Line2D, Rect2D, Vec2D, addV2D, area, isEntirelyWithin, normalizeRect, scaleV2D, subtractV2D, transformLine, transformRect } from "./geometry";
+
+import "./VisualEditor.css";
+import { getBBoxInSvgCoords } from "./svg_helper";
+
+
+type Rountangle = {
+  uid: string;
+  kind: "and" | "or";
+} & Rect2D;
+
+type Text = {
+  uid: string;
+  topLeft: Vec2D;
+  text: string;
+};
+
+type Arrow = {
+  uid: string;
+} & Line2D;
+
+type VisualEditorState = {
+  rountangles: Rountangle[];
+  texts: Text[];
+  arrows: Arrow[];
+  nextID: number;
+};
+
+const emptyState = {
+  rountangles: [], texts: [], arrows: [], nextID: 0,
+};
+
+const onOffStateMachine = {
+  rountangles: [
+    { uid: "0", topLeft: {x: 100, y: 100}, size: {x: 100, y: 100}, kind: "and" },
+    { uid: "1", topLeft: {x: 100, y: 300}, size: {x: 100, y: 100}, kind: "and" },
+  ],
+  texts: [],
+  arrows: [
+    { uid: "2", start: {x: 150, y: 200}, end: {x: 160, y: 300} },
+  ],
+  nextID: 3,
+};
+
+type DraggingState = {
+  lastMousePos: Vec2D;
+} | null; // null means: not dragging
+
+type ResizingState = {
+  lastMousePos: Vec2D;
+} | null; // null means: not resizing
+
+type SelectingState = Rect2D | null;
+
+
+// independently moveable parts of our shapes:
+type RountanglePart = "left" | "top" | "right" | "bottom";
+type ArrowPart = "start" | "end";
+
+type RountangleSelectable = {
+  kind: "rountangle";
+  parts: RountanglePart[];
+  uid: string;
+}
+type ArrowSelectable = {
+  kind: "arrow";
+  parts: ArrowPart[];
+  uid: string;
+}
+type Selectable = RountangleSelectable | ArrowSelectable;
+type Selection = Selectable[];
+
+const minStateSize = {x: 40, y: 40};
+
+export function VisualEditor() {
+  const [state, setState] = useState<VisualEditorState>(onOffStateMachine);
+  const [dragging, setDragging] = useState<DraggingState>(null);
+  const [resizing, setResizing] = useState<ResizingState>(null);
+
+  const [mode, setMode] = useState<"state"|"transition"|"text">("state");
+
+  const [showHelp, setShowHelp] = useState<boolean>(true);
+
+  // uid's of selected rountangles
+  const [selection, setSelection] = useState<Selection>([]);
+
+  // not null while the user is making a selection
+  const [selectingState, setSelectingState] = useState<SelectingState>(null);
+
+  const refSVG = useRef<SVGSVGElement>(null);
+
+  // useEffect(() => {
+  //   console.log('selection:', selection);
+  // }, [selection]);
+  // useEffect(() => {
+  //   console.log('state:', state);
+  // }, [state]);
+  // useEffect(() => {
+  //   console.log('selectingState:', selectingState);
+  // }, [selectingState]);
+
+
+
+  const onMouseDown: MouseEventHandler<SVGSVGElement> = (e) => {
+    console.log(e);
+    const currentPointer = {x: e.clientX, y: e.clientY};
+
+    if (e.button === 1) {
+      // ignore selection, always insert rountangle
+      setState(state => {
+        const newID = state.nextID.toString();
+        setSelection([newID]);
+        return {
+          ...state,
+          rountangles: [...state.rountangles, {
+            uid: newID,
+            topLeft: currentPointer,
+            size: minStateSize,
+            kind: "and",
+          }],
+          nextID: state.nextID+1,
+        };
+      });
+      setResizing({lastMousePos: currentPointer});
+    }
+    else if (e.button === 0) {
+      const uid = e.target?.dataset.uid;
+      const parts: string[] = e.target?.dataset.parts?.split(' ') || [];
+      if (uid) {
+        let allPartsInSelection = true;
+        for (const part of parts) {
+          if (!(selection.find(s => s.uid === uid)?.parts || []).includes(part)) {
+            allPartsInSelection = false;
+            break;
+          }
+        }
+        if (!allPartsInSelection) {
+          setSelection([{uid, parts, kind: "dontcare"}]);
+        }
+
+        // left mouse button: select and drag
+          setDragging({
+            lastMousePos: currentPointer,
+          });
+        // // right mouse button: select and resize
+        // else if (e.button === 2) {
+        //   setResizing({
+        //     lastMousePos: currentPointer,
+        //   });
+        // }
+      }
+      else {
+        setDragging(null);
+        setResizing(null);
+        setSelectingState({
+          topLeft: currentPointer,
+          size: {x: 0, y: 0},
+        });
+        setSelection([]);
+      }
+    }
+  };
+
+  const onMouseMove = (e: MouseEvent) => {
+    const currentPointer = {x: e.clientX, y: e.clientY};
+    if (dragging) {
+      setDragging(prevDragState => {
+        const pointerDelta = subtractV2D(currentPointer, dragging.lastMousePos);
+        const halfPointerDelta = scaleV2D(pointerDelta, 0.5);
+        setState(state => ({
+          ...state,
+          rountangles: state.rountangles.map(r => {
+            const parts = selection.find(selected => selected.uid === r.uid)?.parts || [];
+            if (parts.length === 0) {
+              return r;
+            }
+            return {
+              uid: r.uid,
+              kind: r.kind,
+              ...transformRect(r, parts, halfPointerDelta),
+            };
+          }),
+          arrows: state.arrows.map(a => {
+            const parts = selection.find(selected => selected.uid === a.uid)?.parts || [];
+            if (parts.length === 0) {
+              return a;
+            }
+            return {
+              uid: a.uid,
+              ...transformLine(a, parts, halfPointerDelta),
+            }
+          })
+        }));
+        return {lastMousePos: currentPointer};
+      });
+    }
+    else if (resizing) {
+      setResizing(prevResizeState => {
+        const pointerDelta = subtractV2D(currentPointer, prevResizeState!.lastMousePos);
+        const halfPointerDelta = scaleV2D(pointerDelta, 0.5);
+        setState(state => ({
+          ...state,
+          rountangles: state.rountangles.map(r => {
+            if (selection.includes(r.uid)) {
+              const newSize = addV2D(r.size, halfPointerDelta);
+              return {
+                ...r,
+                size: {
+                  x: Math.max(newSize.x, minStateSize.x),
+                  y: Math.max(newSize.y, minStateSize.y),
+                },
+              };
+            }
+            else {
+              return r; // no change
+            }
+          }),
+        }));
+        return {lastMousePos: currentPointer};
+      });
+    }
+    else if (selectingState) {
+      setSelectingState(ss => {
+        const selectionSize = subtractV2D(currentPointer, ss!.topLeft);
+        return {
+          ...ss!,
+          size: selectionSize,
+        };
+      });
+    }
+  };
+
+  const onMouseUp = (e: MouseEvent) => {
+    setDragging(null);
+    setResizing(null);
+    setSelectingState(ss => {
+      if (ss) {
+        // we were making a selection
+        const normalizedSS = normalizeRect(ss);
+
+        const shapes = Array.from(refSVG.current?.querySelectorAll("rect, line, circle") || []) as SVGGraphicsElement[];
+
+        const shapesInSelection = shapes.filter(el => {
+          const bbox = getBBoxInSvgCoords(el, refSVG.current!);
+          return isEntirelyWithin(bbox, normalizedSS);
+        }).filter(el => !el.classList.contains("corner"));
+
+        const uidToParts = new Map();
+        for (const shape of shapesInSelection) {
+          const uid = shape.dataset.uid;
+          if (uid) {
+            const parts: Set<string> = uidToParts.get(uid) || new Set();
+            for (const part of shape.dataset.parts?.split(' ') || []) {
+              parts.add(part);
+            }
+            uidToParts.set(uid, parts);
+          }
+        }
+
+        setSelection(() => [...uidToParts.entries()].map(([uid,parts]) => ({
+          kind: "rountangle",
+          uid,
+          parts: [...parts],
+        })));
+
+        // const selected = [
+        //   ...state.rountangles.filter(rountangle =>
+        //   isEntirelyWithin(rountangle, normalizedSS)),
+
+        //   ...state.arrows.filter(arrow => isEntirelyWithin({
+        //     topLeft: arrow.start,
+        //     size: subtractV2D(arrow.end, arrow.start),
+        //   }, normalizedSS)),
+        // ];
+        // setSelection(selected.map(r => r.uid));
+      }
+      return null; // no longer selecting
+    });
+    // sort: smaller rountangles are drawn on top
+    setState(state => ({
+      ...state,
+      rountangles: state.rountangles.toSorted((a,b) => area(b) - area(a)),
+    }));
+  };
+
+  const onKeyDown = (e: KeyboardEvent) => {
+    if (e.key === "Delete") {
+      // delete selection
+      setSelection(selection => {
+        setState(state => ({
+          ...state,
+          rountangles: state.rountangles.filter(r => !selection.includes(r.uid)),
+        }));
+        return [];
+      });
+    }
+    if (e.key === "o") {
+      console.log('turn selected states into OR-states...');
+      // selected states become OR-states
+      setSelection(selection => {
+        setState(state => ({
+          ...state,
+          rountangles: state.rountangles.map(r => selection.includes(r.uid) ? ({...r, kind: "or"}) : r),
+        }));
+        return selection;
+      })
+    }
+    if (e.key === "a") {
+      // selected states become AND-states
+      setSelection(selection => {
+        setState(state => ({
+          ...state,
+          rountangles: state.rountangles.map(r => selection.includes(r.uid) ? ({...r, kind: "and"}) : r),
+        }));
+        return selection;
+      });
+    }
+    if (e.key === "h") {
+      setShowHelp(showHelp => !showHelp);
+    }
+    if (e.key === "s") {
+      setMode("state");
+    }
+    if (e.key === "t") {
+      setMode("transition");
+    }
+    if (e.key === "x") {
+      setMode("text");
+    }
+  };
+
+  useEffect(() => {
+    // mousemove and mouseup are global event handlers so they keep working when pointer is outside of browser window
+    window.addEventListener("mouseup", onMouseUp);
+    window.addEventListener("mousemove", onMouseMove);
+    window.addEventListener("keydown", onKeyDown);
+    return () => {
+      window.removeEventListener("keydown", onKeyDown);
+      window.removeEventListener("mousemove", onMouseMove);
+      window.removeEventListener("mouseup", onMouseUp);
+    };
+  }, [selectingState, dragging, resizing]);
+
+  return <svg width="100%" height="100%"
+      className="svgCanvas"
+      onMouseDown={onMouseDown}
+      onContextMenu={e => e.preventDefault()}
+      ref={refSVG}
+    >
+      <defs>
+        <marker
+          id="arrowEnd"
+          viewBox="0 0 10 10"
+          refX="5"
+          refY="5"
+          markerWidth="6"
+          markerHeight="6"
+          orient="auto-start-reverse">
+          <path d="M 0 0 L 10 5 L 0 10 z" />
+        </marker>
+      </defs>
+
+    {state.rountangles.map(rountangle => <RountangleSVG
+      key={rountangle.uid}
+      rountangle={rountangle}
+      dragging={(dragging!==null) && selection.includes(rountangle.uid)}
+      selected={selection.find(r => r.uid === rountangle.uid)?.parts || []}
+      />)}
+
+    {state.arrows.map(arrow => <ArrowSVG
+      key={arrow.uid}
+      arrow={arrow}
+      dragging={(dragging!==null) && selection.includes(arrow.uid)}
+      selected={selection.find(a => a.uid === arrow.uid)?.parts || []}
+      />
+    )}
+
+    {selectingState && <Selecting {...selectingState} />}
+
+    {showHelp && <>
+      <text x={5} y={20}>
+        Left mouse button: Select/Drag.
+      </text>
+      <text x={5} y={40}>
+        Right mouse button: Resize.
+      </text>
+      <text x={5} y={60}>
+        Middle mouse button: Insert [S]tates / [T]ransitions / Te[X]t (current mode: {mode})</text>
+      <text x={5} y={80}>
+        [Del] Delete selection.
+      </text>
+      <text x={5} y={100}>
+        [O] Turn selected states into OR-states.
+      </text>
+      <text x={5} y={120}>
+        [A] Turn selected states into AND-states.
+      </text>
+      <text x={5} y={140}>
+        [H] Show/hide this help.
+      </text>
+    </>}
+
+  </svg>;
+}
+
+const cornerOffset = 4;
+const cornerRadius = 16;
+
+export function RountangleSVG(props: {rountangle: Rountangle, dragging: boolean, selected: string[]}) {
+  const {topLeft, size, uid} = props.rountangle;
+  return <g transform={`translate(${topLeft.x} ${topLeft.y})`}>
+    <rect
+      className={"rountangle"
+        +(props.dragging?" dragging":"")
+        // +(props.selected.length===4?" selected":"")
+        +((props.rountangle.kind==="or")?" or":"")}
+      rx={20} ry={20}
+      x={0}
+      y={0}
+      width={size.x}
+      height={size.y}
+      data-uid={uid}
+      data-parts="left top right bottom"
+    />
+    <line
+      className={"lineHelper"
+        +(props.selected.includes("top")?" selected":"")}
+      x1={0}
+      y1={0}
+      x2={size.x}
+      y2={0}
+      data-uid={uid}
+      data-parts="top"
+    />
+    <line
+      className={"lineHelper"
+        +(props.selected.includes("right")?" selected":"")}
+      x1={size.x}
+      y1={0}
+      x2={size.x}
+      y2={size.y}
+      data-uid={uid}
+      data-parts="right"
+    />
+    <line
+      className={"lineHelper"
+        +(props.selected.includes("bottom")?" selected":"")}
+      x1={0}
+      y1={size.y}
+      x2={size.x}
+      y2={size.y}
+      data-uid={uid}
+      data-parts="bottom"
+    />
+    <line
+      className={"lineHelper"
+        +(props.selected.includes("left")?" selected":"")}
+      x1={0}
+      y1={0}
+      x2={0}
+      y2={size.y}
+      data-uid={uid}
+      data-parts="left"
+    />
+
+    <circle
+      className="circleHelper corner"
+      cx={cornerOffset}
+      cy={cornerOffset}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="top left"
+      />
+
+    <circle
+      className="circleHelper corner"
+      cx={size.x-cornerOffset}
+      cy={cornerOffset}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="top right"
+      />
+
+    <circle
+      className="circleHelper corner"
+      cx={size.x-cornerOffset}
+      cy={size.y-cornerOffset}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="bottom right"
+      />
+
+    <circle
+      className="circleHelper corner"
+      cx={cornerOffset}
+      cy={size.y-cornerOffset}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="bottom left"
+      />
+
+
+
+    <text x={10} y={20}>{uid}</text>
+  </g>;
+}
+
+export function ArrowSVG(props: {arrow: Arrow, dragging: boolean, selected: string[]}) {
+  const {start, end, uid} = props.arrow;
+  return <g>
+    <line
+      className={"arrow"
+        +(props.dragging?" dragging":"")
+        // +(props.selected.length===2?" selected":"")
+      }
+      markerEnd='url(#arrowEnd)'
+      x1={start.x}
+      y1={start.y}
+      x2={end.x}
+      y2={end.y}
+      data-uid={uid}
+      data-parts="start end"
+    />
+    <line
+      className="lineHelper"
+      x1={start.x}
+      y1={start.y}
+      x2={end.x}
+      y2={end.y}
+      data-uid={uid}
+      data-parts="start end"
+    />
+
+    <circle
+      className={"circleHelper"
+        +(props.selected.includes("start")?" selected":"")}
+      cx={start.x}
+      cy={start.y}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="start"
+    />
+    <circle
+      className={"circleHelper"
+        +(props.selected.includes("end")?" selected":"")}
+      cx={end.x}
+      cy={end.y}
+      r={cornerRadius}
+      data-uid={uid}
+      data-parts="end"
+    />
+  </g>;
+}
+
+export function Selecting(props: SelectingState) {
+  const normalizedRect = normalizeRect(props!);
+  return <rect
+    className="selecting"
+    x={normalizedRect.topLeft.x}
+    y={normalizedRect.topLeft.y}
+    width={normalizedRect.size.x}
+    height={normalizedRect.size.y}
+  />;
+}

src/VisualEditor/geometry.ts

@@ -0,0 +1,93 @@
+export type Vec2D = {
+  x: number;
+  y: number;
+};
+
+export type Rect2D = {
+  topLeft: Vec2D;
+  size: Vec2D;
+};
+
+export type Line2D = {
+  start: Vec2D;
+  end: Vec2D;
+};
+
+// make sure size is always positive
+export function normalizeRect(rect: Rect2D) {
+  return {
+    topLeft: {
+      x: rect.size.x < 0 ? (rect.topLeft.x + rect.size.x) : rect.topLeft.x,
+      y: rect.size.y < 0 ? (rect.topLeft.y + rect.size.y) : rect.topLeft.y,
+    },
+    size: {
+      x: rect.size.x < 0 ? -rect.size.x : rect.size.x,
+      y: rect.size.y < 0 ? -rect.size.y : rect.size.y,
+    }
+  };
+}
+
+export function isEntirelyWithin(child: Rect2D, parent: Rect2D) {
+  return (
+    child.topLeft.x >= parent.topLeft.x
+    && child.topLeft.y >= parent.topLeft.y
+    && child.topLeft.x + child.size.x <= parent.topLeft.x + parent.size.x
+    && child.topLeft.y + child.size.y <= parent.topLeft.y + parent.size.y
+  );
+}
+
+export function isWithin(p: Vec2D, r: Rect2D) {
+  return (
+       p.x >= r.topLeft.x && p.x <= r.topLeft.x + r.size.x
+    && p.y >= r.topLeft.y && p.y <= r.topLeft.y + r.size.y
+  );
+}
+
+export function addV2D(a: Vec2D, b: Vec2D) {
+  return {
+    x: a.x + b.x,
+    y: a.y + b.y,
+  };
+}
+
+export function subtractV2D(a: Vec2D, b: Vec2D) {
+  return {
+    x: a.x - b.x,
+    y: a.y - b.y,
+  };
+}
+
+export function scaleV2D(p: Vec2D, scale: number) {
+  return {
+    x: p.x * scale,
+    y: p.y * scale,
+  };
+}
+
+export function area(rect: Rect2D) {
+  return rect.size.x * rect.size.y;
+}
+
+export function transformRect(rect: Rect2D, parts: string[], delta: Vec2D): Rect2D {
+  return {
+    topLeft: {
+      x: parts.includes("left") ? rect.topLeft.x + delta.x : rect.topLeft.x,
+      y: parts.includes("top") ? rect.topLeft.y + delta.y : rect.topLeft.y,
+    },
+    size: {
+      x: rect.size.x
+        + (parts.includes("right") ? delta.x : 0)
+        - (parts.includes("left")  ? delta.x : 0),
+      y: rect.size.y
+        + (parts.includes("bottom") ? delta.y : 0)
+        - (parts.includes("top")    ? delta.y : 0),
+    },
+  };
+}
+
+export function transformLine(line: Line2D, parts: string[], delta: Vec2D): Line2D {
+  return {
+    start: parts.includes("start") ? addV2D(line.start, {x: delta.x, y: delta.y}) : line.start,
+    end: parts.includes("end") ? addV2D(line.end, {x: delta.x, y: delta.y}) : line.end,
+  };
+}

src/VisualEditor/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),
+    },
+  };
+}