Support dpi other than 96dpi

Automattic / node-canvas

Node canvas is a Cairo backed Canvas implementation for NodeJS.

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Support dpi other than 96dpi #99

Open jakeg opened 13 years ago

jakeg commented 13 years ago

I guess V8 thinks we're on a screen with 96dpi. I think wkhtmltopdf provides an option to change this to eg 300dpi instead.

To reproduce:

ctx.font = '9pt arial';
open and compare to eg Photoshop text at 9pt
notice it's much smaller

To (temporarily) fix:

pt = function(screen_pt) { return screen_pt / 96 * 300; // presumably? } ctx.font = pt(9) + 'pt arial';

tj commented 13 years ago

v8 doesn't have anything to do with it :p, it's in lib/context2d.js I have a few TODOs in there, more specifically the parseFont method

tnunes commented 7 years ago

Any update on this issue?

LinusU commented 5 years ago

Would love some more details on how you want this to work.

How does it work in web browsers?
Is there anything similar in OffscreenCanvas?
Is this only for changing pt in font size, or is there more to it?

chrisspiegl commented 2 years ago

I just was trying to figure out the same thing. How to get higher DPI when creating PNG images in node.js.

I found out that when rendering image/png to base64 I could use the pngConfig setting.

myCanvas.toBuffer('image/png', {
  resolution: 74 * scale,
});

I am not yet 100% sure how exactly this works, but I found that in my use case it does increase the resolution of the image without changing the size. Something like that.

zbjornson commented 2 years ago

All the resolution setting does is set the pHYs chunk in the header. It's an ancillary chunk though and at least Chrome and Firefox ignore it. I imagine some image editing apps use it.

chrisspiegl commented 2 years ago

@zbjornson Thanks for the additional info. I am using this in the menu bar of macOS via xbar (the plugin I created shows the current download/upload speed of my internet connection).

There the resolution setting seems to help quit a lot and does the trick to increase the quality of the image displayed on my retina and non retina displays.