Add cubic bezier curve visual debug

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

excalidraw-app/components/DebugCanvas.tsx

@@ -12,9 +12,10 @@ import {
   TrashIcon,
 } from "../../packages/excalidraw/components/icons";
 import { STORAGE_KEYS } from "../app_constants";
-import type { Arc } from "../../packages/math";
+import type { Arc, CubicBezier } from "../../packages/math";
 import {
   isArc,
+  isBezier,
   isSegment,
   type GlobalPoint,
   type Segment,
@@ -35,6 +36,28 @@ const renderLine = (
   context.restore();
 };
 
+const renderCubicBezier = (
+  context: CanvasRenderingContext2D,
+  zoom: number,
+  { start, control1, control2, end }: CubicBezier<GlobalPoint>,
+  color: string,
+) => {
+  context.save();
+  context.strokeStyle = color;
+  context.beginPath();
+  context.moveTo(start[0] * zoom, start[1] * zoom);
+  context.bezierCurveTo(
+    control1[0] * zoom,
+    control1[1] * zoom,
+    control2[0] * zoom,
+    control2[1] * zoom,
+    end[0] * zoom,
+    end[1] * zoom,
+  );
+  context.stroke();
+  context.restore();
+};
+
 const renderArc = (
   context: CanvasRenderingContext2D,
   zoom: number,
@@ -90,6 +113,16 @@ const render = (
           el.color,
         );
         break;
+      case isBezier(el.data):
+        renderCubicBezier(
+          context,
+          appState.zoom.value,
+          el.data as CubicBezier<GlobalPoint>,
+          el.color,
+        );
+        break;
+      default:
+        throw new Error("Unknown element type");
     }
   });
 };

packages/excalidraw/visualdebug.ts

@@ -1,4 +1,4 @@
-import type { Arc, Segment } from "../math";
+import type { Arc, CubicBezier, Segment } from "../math";
 import { isSegment, segment, pointFrom, type GlobalPoint } from "../math";
 import { isBounds } from "./element/typeChecks";
 import type { Bounds } from "./element/types";
@@ -15,10 +15,24 @@ declare global {
 
 export type DebugElement = {
   color: string;
-  data: Segment<GlobalPoint> | Arc<GlobalPoint>;
+  data: Segment<GlobalPoint> | Arc<GlobalPoint> | CubicBezier<GlobalPoint>;
   permanent: boolean;
 };
 
+export const debugDrawCubicBezier = (
+  c: CubicBezier<GlobalPoint>,
+  opts?: {
+    color?: string;
+    permanent?: boolean;
+  },
+) => {
+  addToCurrentFrame({
+    color: opts?.color ?? "purple",
+    permanent: !!opts?.permanent,
+    data: c,
+  });
+};
+
 export const debugDrawArc = (
   a: Arc<GlobalPoint>,
   opts?: {

packages/math/curve.ts

@@ -1,5 +1,5 @@
-import { pointFrom, pointRotateRads } from "./point";
-import type { Curve, GenericPoint, Radians } from "./types";
+import { isPoint, pointFrom, pointRotateRads } from "./point";
+import type { CubicBezier, Curve, GenericPoint, Radians } from "./types";
 
 /**
  *
@@ -221,3 +221,20 @@ const findClosestParameter = <Point extends GenericPoint>(
 
   return closestT;
 };
+
+export const isBezier = <Point extends GenericPoint>(
+  c: unknown,
+): c is CubicBezier<Point> => {
+  return (
+    c != null &&
+    typeof c === "object" &&
+    Object.hasOwn(c, "start") &&
+    Object.hasOwn(c, "end") &&
+    Object.hasOwn(c, "control1") &&
+    Object.hasOwn(c, "control2") &&
+    isPoint((c as CubicBezier<Point>).start) &&
+    isPoint((c as CubicBezier<Point>).end) &&
+    isPoint((c as CubicBezier<Point>).control1) &&
+    isPoint((c as CubicBezier<Point>).control2)
+  );
+};

packages/math/types.ts

@@ -132,9 +132,11 @@ export type Extent = {
   _brand: "excalimath_extent";
 };
 
-// an ellipse is specified by its center, angle, and its major and minor axes
-// but for the sake of simplicity, we've used halfWidth and halfHeight instead
-// in replace of semi major and semi minor axes
+/**
+  An ellipse is specified by its center, angle, and its major and minor axes
+  but for the sake of simplicity, we've used halfWidth and halfHeight instead
+  in replace of semi major and semi minor axes
+ */
 export type Ellipse<Point extends GenericPoint> = {
   center: Point;
   halfWidth: number;
@@ -142,3 +144,14 @@ export type Ellipse<Point extends GenericPoint> = {
 } & {
   _brand: "excalimath_ellipse";
 };
+
+/**
+ * Represents a cubic bezier with 2 control points on the point space of your
+ * choosing.
+ */
+export type CubicBezier<P extends GenericPoint> = {
+  start: P;
+  end: P;
+  control1: P;
+  control2: P;
+};