726227 - Canvas ignores really small font size

Status: NEW

(Core :: Graphics: Canvas2D, defect)

Description

[Yury Delendik (:yury)]

Attachment: Minimal test case for minimal font problem

The following fragment ignores or not properly sets the 2d context font:

  ctx.font = "0.2px serif";
  ctx.scale(60,60);
  ctx.fillText("test", 10/60, 25/60);

The actual result is the text is larger that 12px.

The expected result is the text with size 12px.

(see also https://github.com/mozilla/pdf.js/issues/1169)

Comment 1

[Boris Zbarsky [:bzbarsky]]

I wonder whether we clamp font sizes to at least 1px somewhere...

Comment 2

[Jonathan Kew [:jfkthame]]

(In reply to Boris Zbarsky (:bz) from comment #1)
> I wonder whether we clamp font sizes to at least 1px somewhere...

We definitely do this in some font backends, e.g.:
http://mxr.mozilla.org/mozilla-central/source/gfx/thebes/gfxMacFont.cpp#248

But I don't know offhand how this interacts with canvas scaling. If we're instantiating a "tiny" font and then relying on scaling in the cairo context to make it bigger, I can imagine this would be a problem.

(It'd remain something a problem, at least under GDI, even for larger sizes because we round the font size to integer pixels.)

I note that the testcase doesn't work properly in Safari, Chrome, or Opera either.

Comment 3

[Boris Zbarsky [:bzbarsky]]

> If we're instantiating a "tiny" font and then relying on scaling in the cairo context to 
> make it bigger

That's exactly what the testcase is doing, yes.