Trying to modify ImageData in PDF: FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal.

[paramsiddharth]

The error comes when attempting to retrieve and modify an ImageData object in a canvas of type PDF.
It works fine for canvases with only dimensions provided as parameters.

FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal.
 1: 0xa6ae50 node::Abort() [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 2: 0x99dc4d node::FatalError(char const*, char const*) [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 3: 0xc4b0aa v8::Utils::ReportApiFailure(char const*, char const*) [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 4: 0x7f1644465324 Context2d::GetImageData(Nan::FunctionCallbackInfo<v8::Value> const&) [/home/param/myprojects/rema/rema/src/node_modules/canvas/build/Release/canvas.node]
 5: 0x7f1644458d58  [/home/param/myprojects/rema/rema/src/node_modules/canvas/build/Release/canvas.node]
 6: 0xcb7d1b  [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 7: 0xcb92cc  [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 8: 0xcb9946 v8::internal::Builtin_HandleApiCall(int, unsigned long*, v8::internal::Isolate*) [/home/param/.nvm/versions/node/v15.6.0/bin/node]
 9: 0x14d8b79  [/home/param/.nvm/versions/node/v15.6.0/bin/node]

Issue or Feature

Retrieving ImageData using .getImageData, modifying it, and putting it back fails for canvases of type PDF.

Steps to Reproduce

const { createCanvas } = require('canvas');
const canvas = createCanvas(200, 200, 'pdf');
const ctx = canvas.getContext('2d');

// Do something
// ...
// Later

/*
	Attempted colour inversion of a section (there is another way to achieve
	this using ctx.globalCompositeOperation
	and YES that works even for PDF type canvases)
*/
const value = ctx.getImageData(0, 0, 100, 100);
const data = value.data;
for (let i = 0; i < data.length; i += 4) {
	data[i]     = 255 - data[i];     // Red
	data[i + 1] = 255 - data[i + 1]; // Green
	data[i + 2] = 255 - data[i + 2]; // Blue
}

const tmpCanvas = createCanvas(100, 100);
const tmpCtx = tmpCanvas.getContext('2d');
tmpCtx.putImageData(value, 0, 0);
value = tmpCanvas.toDataURL();

Your Environment

• Version of node-canvas (output of npm list canvas or yarn list canvas): 2.8.0
• Environment (e.g. node 4.2.0 on Mac OS X 10.8): Tested on Node.js v14.17.3 and v15.6.0 on Ubuntu 20.04 WSL.

[zbjornson]

It's not possible to work with image data (pixel values) for a PDF or SVG canvas. #1961 will make this throw an error instead of crashing the process. Thanks for finding the bug.