[with solution]: Problem with context.save () and context.restore ()

[tmarti]

The problem

The jest-canvas-mock/CanvasRenderingContext2D class save and restore operations should behave in the same way as browser/CanvasRenderingContext2D but it doesn't.

If we execute the following code:

function _do (cont) {
    var tmp = [];
    
    cont.scale(0.5, 0.5);
    cont.save ();
    tmp.push (cont.getTransform ().m11);
    cont.scale (0.5, 0.5);
    tmp.push (cont.getTransform ().m11);
    cont.restore ();
    tmp.push (cont.getTransform ().m11);
    
    console.log (tmp);
}

var the_canvas = some real canvas;

console.log ("save/restore sequence for browser/CanvasRenderingContext2D")

_do (
    the_canvas.getContext('2d')
);

console.log ("save/restore sequence for jest-canvas-mock/CanvasRenderingContext2D")

_do (
    new CanvasRenderingContext2D (
        the_canvas
    )
);

We get the following output:

save/restore sequence for browser/CanvasRenderingContext2D
Array(3) [ 0.5, 0.25, 0.5 ]

save/restore sequence for jest-canvas-mock/CanvasRenderingContext2D
Array(3) [ 0.5, 0.25, 0.25 ]

Expected behaviour

The output for jest-canvas-mock/CanvasRenderingContext2D should be the same as browser/CanvasRenderingContext2D...

Array(3) [ 0.5, 0.25, 0.5 ]

... instead of...

Array(3) [ 0.5, 0.25, 0.25 ]

(notice the 0.25 intead of 0.5 as last element in the array)

[tmarti]

The solution

There we go!

The line...

jest-canvas-mock/src/classes/CanvasRenderingContext2D.js

Line 1103 in d895824

this._transformStack.push(this._transformStack[this._stackIndex]);

... needs to be changed to...

this._transformStack.push(this._transformStack[this._stackIndex].slice ());

(notice the .slice())

[jtenner]

@tmarti Thank you so much for this catch. This is a really easy fix, and you can submit a pull request if you'd like.

[hustcc]

@tmarti Mock canvas when run unit test cases with jest. For more browser environment, you can use
jest-electron for real browser runtime.

[jtenner]

I'm going to take care of this in a few days. Sorry for the wait.