Bug 155789 – Printed PDF renders incorrect font sizes

• Status: NEW
• Component: Printing

[Joe]

Created attachment 274745 [details]
Sample HTML file for testing, with font sizes set in pt. Also includes output .pdf files from different browsers

Overview: Printing from webkit renders font sizes incorrectly. This bug was first discovered on iOS, but I have since produced it on Mac Safari and Chrome.

Steps to Reproduce: 
1. Use sample.html from attachments, or any HTML page that sets font sizes that can be accurately measured against.
2. Print .html page using print dialog, then save as a PDF.
3. Open saved .pdf file in Adobe Acrobat, then inspect PDF font sizes using the 'Edit' mode.

Actual Results:
Depending on what software used, font sizes are not the same as specified in the html code. For example, the attachment I provide from Safari has font sizes of 12.80pt, 10.40pt, 8.80pt, 16.80pt and 24.80pt - none of which are correct.

Expected Results:
Font sizes on PDF should match exactly with sizes set in HTML. The attachment I provide from Safari should have font sizes of 12pt, 10pt, 8pt, 16pt, and 23pt.

Build Date & Platform: 
Currently reporting it using Mac Safari Version 9.0.1 (11601.2.7.2), Mac Chrome Version 49.0.2623.87 (64-bit), and iOS 9.x.x - but have experienced it over many versions.

Additional Builds and Platforms:
This bug does not occur on Mac Firefox 41.0.2. PDF's rendered from Firefox have correct font sizes.

Additional Information: 
- This bug was first discovered when using UIPrintPageRenderer on iOS to create PDF files from .html input.
- I have performed additional tests using other font units (px, em, %), but the bug still occurs. The sample HTML file uses pt as a unit as this is easiest to measure in the outputted PDF.
- Using '-webkit-text-size-adjust: none;' as a possible workaround did not effect the outcome.
- Using '<meta name="viewport" content="initial-scale=1.0" />' as a possible workaround did not effect the outcome.