Scrolling in RichTextLabel ignores visible_characters property (fixed in master)

[dalexeev]

Godot version:
3.2.1.stable.official

OS/device including version:
Linux

Issue description:
If text does not fit in height and visible_characters is used (for the typewriter effect), then the text is not displayed as expected.

1. scroll_active == true and scroll_following == false:
   There is an opportunity to scroll through unnecessary empty space.

2. scroll_active == false and scroll_following == true:
   First you see empty space, then (when visible_characters is incremented by a script) you see the end of the phrase.

Proposed solution: RichTextLabel should only consider visible lines when scrolling.

Steps to reproduce:

Minimal reproduction project:
rtl_scroll_bug.zip

[dalexeev]

Fixed in 4.0-dev.

[brianrodri]

Seems this has only been fixed for VisibleCharactersBehavior.VC_CHARS_BEFORE_SHAPING.

Still seeing the same bug when using: VisibleCharactersBehavior.VC_CHARS_AFTER_SHAPING.

Minimal reproduction project (v4.3): rtl_scroll_bug.zip

[Calinou]

I wonder if #78916 has any impact on this.

cc @bruvzg

[brianrodri]

Taking a look at #55636, which seems to be the fix referenced by #37720 (comment), I only see handling for VC_CHARS_BEFORE_SHAPING in the size calculation code:

godot/scene/gui/rich_text_label.cpp

Lines 520 to 523 in 97ef3c8

	for (Item *it = l.from; it && it != it_to; it = _get_next_item(it)) {
	if (visible_chars_behavior == TextServer::VC_CHARS_BEFORE_SHAPING && visible_characters >= 0 && remaining_characters <= 0) {
	break;
	}

godot/scene/gui/rich_text_label.cpp

Lines 575 to 577 in 97ef3c8

	if (visible_chars_behavior == TextServer::VC_CHARS_BEFORE_SHAPING && visible_characters >= 0 && remaining_characters >= 0) {
	tx = tx.substr(0, remaining_characters);
	}

Is VC_CHARS_AFTER_SHAPING omitted intentionally here? Would appreciate some guidance on what the logic is trying to do here so I can attempt a fix!