`exporter.toSVG` mutates models unexpectedly

[xavi-]

It looks like the toSVG method mutates the models passed into it, which is expected. This came up while trying to cache submodels to improve performance.

Here's a minimal repro case:

const makerjs = require("makerjs");
const opentype = require("opentype.js");

const font = opentype.loadSync("./src/fonts/ReliefSingleLineCAD-Regular.ttf");

const text = new makerjs.models.Text(font, "Hi", 12);
const model = {
	models: {
		text1: text,
		text2: text,
	},
};

const svg = makerjs.exporter.toSVG(model);
console.log(svg);

The result is this exception:

TypeError: Cannot read properties of undefined (reading 'startT')
    at getActualBezierRange (/Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:8591:43)
    at /Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:8790:37
    at Array.forEach (<anonymous>)
    at /Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:8785:27
    at _loop_3 (/Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:6054:21)
    at Object.findChains (/Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:6058:17)
    at BezierCurve.getBezierSeeds (/Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:8773:31)
    at /Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:6170:73
    at Array.forEach (<anonymous>)
    at swapBezierPathsWithSeeds (/Users/xavi/code/maker-test/server/node_modules/makerjs/dist/index.js:6161:21)

I'm using node v22.11.0 with makerjs@0.18.1 and opentype.js@1.3.4

The issue seems to be somewhere in here:

maker.js/packages/maker.js/src/core/chain.ts

Lines 405 to 453 in 1ed796b

	beziers.forEach(wm => {
	var b = wm.childModel as models.BezierCurve;
	if (swap) {
	//set layer prior to looking for seeds by layer
	if (wm.layer != undefined && wm.layer !== '') {
	b[tempLayerKey] = (b as IModel).layer;
	(b as IModel).layer = wm.layer;
	}
	//use seeds as path, hide the arc paths from findChains()
	var bezierPartsByLayer = models.BezierCurve.getBezierSeeds(b, { byLayers: true, pointMatchingDistance });
	for (var layer in bezierPartsByLayer) {
	var bezierSeeds = bezierPartsByLayer[layer];
	if (bezierSeeds.length > 0) {
	b[tempKey] = b.paths;
	var newPaths: IPathMap = {};
	bezierSeeds.forEach(function (seed, i) {
	seed.layer = layer;
	newPaths['seed_' + i] = seed;
	});
	b.paths = newPaths;
	}
	}
	} else {
	//revert the above
	if (tempKey in b) {
	b.paths = b[tempKey] as IPathMap;
	delete b[tempKey];
	}
	if (tempLayerKey in b) {
	if (b[tempLayerKey] == undefined) {
	delete (b as IModel).layer;
	} else {
	(b as IModel).layer = b[tempLayerKey] as string;
	}
	delete b[tempLayerKey];
	}
	}
	});

It's not obvious to me how to fix it, so I figured I'd open an issue

The exception doesn't occur when useSvgPathOnly option is enabled, which double confirms that the issue is related to the findChains function

Workaround

// Clone submodels
const model = {
	models: {
		text1: makerjs.cloneObject(text),
		text2: makerjs.cloneObject(text),
	},
};

This does works, but it add a bit of overhead. Also, it's surprising that an exporter mutates the underlying model

[danmarshall]

I agree, there should be an expectation of non-mutation during this type of call.