The bug
Underlines in chat and /title command intersect each other, causing an ugly effect when fading.
How to reproduce
Take a screenshot or enter the following command:
/title @a title {"text":"words","underlined":true}
→ ❌ Note how the pixels in the underline between the individual characters of the word "words" are much bolder than they should be when the text is fading in and out.
Note: You can make the effect more obvious by first using the command
/title @a times 100 0 100
Code analysis
Based on 1.11 decompiled using MCP 9.35 rc1
The method net.minecraft.client.gui.FontRenderer.renderStringAtPos(String, boolean)
has a strange condition when drawing underlined text. It enlarges the line one pixel to the left if it should draw underlined text, which is of course always true because it is currently drawing underlined text. Maybe it was supposed to test if the text is italic or unicode? But enlarging the line to the left means that it will overlap if a underlined character is in front of it, which causes this effect.
Removing this should probably not cause any problems.
Examples
Here are some examples:
[media][media]Linked issues
is duplicated by 1
Attachments
Comments 17

Still in 19w11a and 19w11b

Still in 19w12b

Still in 19w13a

Still in 19w14a
Can confirm in 1.18.1.
Can confirm in 1.18.2 and 22w16b.
Can confirm in 1.19 and 22w24a.
Can confirm in 1.19.2.
It enlarges the line one pixel to the left if it should draw underlined text
I'm pretty sure this is intentional. Currently, the underline extends 1 pixel left and 1 pixel right of the character, which causes overlap. If they remove the 1 extra pixel on the left, then the underline won't be symmetrical anymore.
Quote:
Based on 1.11 decompiled using MCP 9.35 rc1
Must affect 1.11