Registering fonts after drawing on canvas seems to work fine?

[jhuckaby]

Documentation Issue?

The docs state (note emphasis):

To use a font file that is not installed as a system font, use registerFont() to register the font with Canvas. This must be done before the Canvas is created.

However, going against the docs and loading the font after creating and drawing into the canvas seems to work just fine for me. My code:

var fs = require('fs');
var Canvas = require('canvas');
var canvas = Canvas.createCanvas(640, 100);
var ctx = canvas.getContext('2d');

ctx.strokeStyle = 'gray';
ctx.fillStyle = 'yellow';
ctx.beginPath();
ctx.rect( 50, 10, 300, 80 );
ctx.fill();
ctx.stroke();

Canvas.registerFont(('futurastd-m.otf'), { family: 'FuturaStdMedium' });

ctx.font = 'normal normal 36px FuturaStdMedium';
ctx.fillStyle = 'black';
ctx.fillText('Now is the time for all good men.', 10, 35);

canvas.createPNGStream().pipe(fs.createWriteStream('output.png'));

Output:

This renders correctly. I guess I was expecting it to crash or something? My question is, is this just a documentation issue? Was the requirement a previous limitation with node-canvas v1 perhaps, now gone with v2?

Your Environment

• Version: node-canvas HEAD revision, compiled from source 2021/11/03 (reported version: 2.8)
• Environment: CentOS Linux release 7.7.1908 (Core)

[jhuckaby]

Update: This has now started to fail (font renders as some kind of generic default) with canvas v2.9.1, when the font is registered after the canvas is created.

Examples:

canvas v2.9.0 (correct font):

canvas v2.9.1 (incorrect font):

So I guess now the order really matters... at least on Linux. macOS doesn't seem to care.

[chearon]

It's been a while since you asked, but the answer is that Pango caches all fonts present on the OS in a FontMap. When you register a custom font, we change the default FontMap, but we don't update the PangoContext stored on the canvas to use that new FontMap. (I'm not sure how it could have worked before. Maybe Pango used to do something differently?).