1479213 - It takes long period to finish rendering when layout.css.control-characters.visible = true

Status: NEW

(Core :: Graphics: Text, defect, P3)

Description

[Alice0775 White]

Attachment: em.html

This is only nightly build for now.
Because the preference is default true on nightly build, but false on release build(62beta and earlier).

Steps to reproduce:
1. set layout.css.control-characters.visible = true in about:config (default on nightly, but not on release build)
2. Open attached html

Actual Results:
It takes long period to finish rendering.
And unresponsive ui for a while

Expected Results
Not so. And UI should not locked

Comment 1

[Alice0775 White]

Attachment: em_utf8.html, specify correct chaset encode

Render almost instantly if you specify correct encoding.

Comment 2

[Jonathan Kew [:jfkthame]]

Drawing the missing-glyph hexboxes is relatively expensive, compared to drawing actual glyphs, and so a page that has huge numbers of them (usually due to encoding errors) gets slow to paint.

Maybe we should create a "hexbox font" instead of using raw drawing calls to render these.