Fix RichTextEffect `visibility` to Account for Skipped Characters.

A picture is easier to describe this issue than words. Basically, rich
text effects allowed for character visibility changes. While doing so
would work properly, the rich text label would render the next `word` in
an offset accounting for the hidden characters (leaving a huge space.)

This patch fixes this issue by keeping track of the amount of
`backtrack` necessary per line.

(cherry picked from commit b3fd4884d7dd2e1c5f5d5dadd8af6ed13ab131ac)

scene/gui/rich_text_label.cpp

@@ -199,6 +199,8 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 	int line_ascent = cfont->get_ascent();
 	int line_descent = cfont->get_descent();
 
+	int backtrack = 0; // for dynamic hidden content.
+
 	int nonblank_line_count = 0; //number of nonblank lines as counted during PROCESS_DRAW
 
 	Variant meta;
@@ -209,6 +211,7 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 	{                                                                                                                                                           \
 		if (p_mode != PROCESS_CACHE) {                                                                                                                          \
 			line++;                                                                                                                                             \
+			backtrack = 0;                                                                                                                                      \
 			if (!line_is_blank) {                                                                                                                               \
 				nonblank_line_count++;                                                                                                                          \
 			}                                                                                                                                                   \
@@ -258,7 +261,7 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 		l.maximum_width = MAX(l.maximum_width, MIN(p_width, wofs + m_width));                                                               \
 		l.minimum_width = MAX(l.minimum_width, m_width);                                                                                    \
 	}                                                                                                                                       \
-	if (wofs + m_width > p_width) {                                                                                                         \
+	if (wofs - backtrack + m_width > p_width) {                                                                                             \
 		line_wrapped = true;                                                                                                                \
 		if (p_mode == PROCESS_CACHE) {                                                                                                      \
 			if (spaces > 0)                                                                                                                 \
@@ -385,6 +388,7 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 					int fw = 0;
 
 					lh = 0;
+
 					if (p_mode != PROCESS_CACHE) {
 						lh = line < l.height_caches.size() ? l.height_caches[line] : 1;
 						line_ascent = line < l.ascent_caches.size() ? l.ascent_caches[line] : 1;
@@ -427,13 +431,12 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 
 					{
 
-						int ofs = 0;
+						int ofs = 0 - backtrack;
 
 						for (int i = 0; i < end; i++) {
 							int pofs = wofs + ofs;
 
 							if (p_mode == PROCESS_POINTER && r_click_char && p_click_pos.y >= p_ofs.y + y && p_click_pos.y <= p_ofs.y + y + lh) {
-								//int o = (wofs+w)-p_click_pos.x;
 
 								int cw = font->get_char_size(c[i], c[i + 1]).x;
 
@@ -476,7 +479,10 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 								bool visible = visible_characters < 0 || ((p_char_count < visible_characters && YRANGE_VISIBLE(y + lh - line_descent - line_ascent, line_ascent + line_descent)) &&
 																				 faded_visibility > 0.0f);
 
+								const bool previously_visible = visible;
+
 								for (int j = 0; j < fx_stack.size(); j++) {
+
 									ItemFX *item_fx = fx_stack[j];
 
 									if (item_fx->type == ITEM_CUSTOMFX && custom_fx_ok) {
@@ -570,6 +576,8 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 									} else {
 										cw = drawer.draw_char(ci, p_ofs + Point2(align_ofs + pofs, y + lh - line_descent) + fx_offset, fx_char, c[i + 1], fx_color);
 									}
+								} else if (previously_visible) {
+									backtrack += font->get_char_size(fx_char, c[i + 1]).x;
 								}
 
 								p_char_count++;
@@ -643,6 +651,7 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 			case ITEM_NEWLINE: {
 
 				lh = 0;
+
 				if (p_mode != PROCESS_CACHE) {
 					lh = line < l.height_caches.size() ? l.height_caches[line] : 1;
 					line_is_blank = true;