Make label sizing algorithm more robust

2 files changed, 134 insertions, 127 deletions

diff --git a/scene/gui/label.cpp b/scene/gui/label.cpp
index c0ef71ee4f..45218773fe 100644
--- a/scene/gui/label.cpp
+++ b/scene/gui/label.cpp
@@ -86,9 +86,7 @@ int Label::get_line_height(int p_line) const {
 	}
 }
 
-void Label::_shape() {
-	bool font_was_dirty = font_dirty;
-
+bool Label::_shape() {
 	Ref<StyleBox> style = theme_cache.normal_style;
 	int width = (get_size().width - style->get_minimum_size().width);
 
@@ -103,7 +101,7 @@ void Label::_shape() {
 		}
 		const Ref<Font> &font = (settings.is_valid() && settings->get_font().is_valid()) ? settings->get_font() : theme_cache.font;
 		int font_size = settings.is_valid() ? settings->get_font_size() : theme_cache.font_size;
-		ERR_FAIL_COND(font.is_null());
+		ERR_FAIL_COND_V(font.is_null(), true);
 		String txt = (uppercase) ? TS->string_to_upper(xl_text, language) : xl_text;
 		if (visible_chars >= 0 && visible_chars_behavior == TextServer::VC_CHARS_BEFORE_SHAPING) {
 			txt = txt.substr(0, visible_chars);
@@ -123,6 +121,7 @@ void Label::_shape() {
 		dirty = false;
 		font_dirty = false;
 		lines_dirty = true;
+		// Note for future maintainers: forgetting stable width here (e.g., setting it to -1) may fix still undiscovered bugs.
 	}
 
 	if (lines_dirty) {
@@ -135,129 +134,136 @@ void Label::_shape() {
 	Size2i prev_minsize = minsize;
 	minsize = Size2();
 
+	bool can_process_lines = false;
 	if (xl_text.length() == 0) {
+		can_process_lines = true;
 		lines_dirty = false;
-		return;
-	}
-
-	// Don't compute minimum size until width is stable (two shape requests in a row with the same width.)
-	// This avoids situations in which the initial width is very narrow and the label would break text
-	// into many very short lines, causing a very tall label that can leave a deformed container.
-	bool width_stabilized = get_size().width == stable_width;
-	stable_width = get_size().width;
+	} else {
+		// With autowrap on, we won't compute the minimum size until width is stable (two shape requests in a
+		// row with the same width.) This avoids situations in which the initial width is very narrow and the label
+		// would break text into many very short lines, causing a very tall label that can leave a deformed container.
+
+		can_process_lines = get_size().width == stable_width || autowrap_mode == TextServer::AUTOWRAP_OFF;
+		stable_width = get_size().width;
+
+		if (can_process_lines) {
+			if (lines_dirty) {
+				BitField<TextServer::LineBreakFlag> autowrap_flags = TextServer::BREAK_MANDATORY;
+				switch (autowrap_mode) {
+					case TextServer::AUTOWRAP_WORD_SMART:
+						autowrap_flags = TextServer::BREAK_WORD_BOUND | TextServer::BREAK_ADAPTIVE | TextServer::BREAK_MANDATORY;
+						break;
+					case TextServer::AUTOWRAP_WORD:
+						autowrap_flags = TextServer::BREAK_WORD_BOUND | TextServer::BREAK_MANDATORY;
+						break;
+					case TextServer::AUTOWRAP_ARBITRARY:
+						autowrap_flags = TextServer::BREAK_GRAPHEME_BOUND | TextServer::BREAK_MANDATORY;
+						break;
+					case TextServer::AUTOWRAP_OFF:
+						break;
+				}
+				autowrap_flags = autowrap_flags | TextServer::BREAK_TRIM_EDGE_SPACES;
 
-	// With autowrap off, there's still a point in shaping before width is stable: to contribute a min width.
-	if (lines_dirty && (width_stabilized || autowrap_mode == TextServer::AUTOWRAP_OFF)) {
-		BitField<TextServer::LineBreakFlag> autowrap_flags = TextServer::BREAK_MANDATORY;
-		switch (autowrap_mode) {
-			case TextServer::AUTOWRAP_WORD_SMART:
-				autowrap_flags = TextServer::BREAK_WORD_BOUND | TextServer::BREAK_ADAPTIVE | TextServer::BREAK_MANDATORY;
-				break;
-			case TextServer::AUTOWRAP_WORD:
-				autowrap_flags = TextServer::BREAK_WORD_BOUND | TextServer::BREAK_MANDATORY;
-				break;
-			case TextServer::AUTOWRAP_ARBITRARY:
-				autowrap_flags = TextServer::BREAK_GRAPHEME_BOUND | TextServer::BREAK_MANDATORY;
-				break;
-			case TextServer::AUTOWRAP_OFF:
-				break;
-		}
-		autowrap_flags = autowrap_flags | TextServer::BREAK_TRIM_EDGE_SPACES;
+				PackedInt32Array line_breaks = TS->shaped_text_get_line_breaks(text_rid, width, 0, autowrap_flags);
+				for (int i = 0; i < line_breaks.size(); i = i + 2) {
+					RID line = TS->shaped_text_substr(text_rid, line_breaks[i], line_breaks[i + 1] - line_breaks[i]);
+					lines_rid.push_back(line);
+				}
+			}
 
-		PackedInt32Array line_breaks = TS->shaped_text_get_line_breaks(text_rid, width, 0, autowrap_flags);
-		for (int i = 0; i < line_breaks.size(); i = i + 2) {
-			RID line = TS->shaped_text_substr(text_rid, line_breaks[i], line_breaks[i + 1] - line_breaks[i]);
-			lines_rid.push_back(line);
-		}
-	}
+			if (autowrap_mode == TextServer::AUTOWRAP_OFF) {
+				for (int i = 0; i < lines_rid.size(); i++) {
+					if (minsize.width < TS->shaped_text_get_size(lines_rid[i]).x) {
+						minsize.width = TS->shaped_text_get_size(lines_rid[i]).x;
+					}
+				}
 
-	if (autowrap_mode == TextServer::AUTOWRAP_OFF) {
-		for (int i = 0; i < lines_rid.size(); i++) {
-			if (minsize.width < TS->shaped_text_get_size(lines_rid[i]).x) {
-				minsize.width = TS->shaped_text_get_size(lines_rid[i]).x;
+				// With autowrap off, by now we already know the width the label will take.
+				width = (minsize.width - style->get_minimum_size().width);
 			}
-		}
 
-		// With autowrap off, by now we already know the width the label will take.
-		width = (minsize.width - style->get_minimum_size().width);
-		width_stabilized = true;
-	}
-
-	if (lines_dirty && width_stabilized) {
-		BitField<TextServer::TextOverrunFlag> overrun_flags = TextServer::OVERRUN_NO_TRIM;
-		switch (overrun_behavior) {
-			case TextServer::OVERRUN_TRIM_WORD_ELLIPSIS:
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM_WORD_ONLY);
-				overrun_flags.set_flag(TextServer::OVERRUN_ADD_ELLIPSIS);
-				break;
-			case TextServer::OVERRUN_TRIM_ELLIPSIS:
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
-				overrun_flags.set_flag(TextServer::OVERRUN_ADD_ELLIPSIS);
-				break;
-			case TextServer::OVERRUN_TRIM_WORD:
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM_WORD_ONLY);
-				break;
-			case TextServer::OVERRUN_TRIM_CHAR:
-				overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
-				break;
-			case TextServer::OVERRUN_NO_TRIMMING:
-				break;
-		}
+			if (lines_dirty) {
+				BitField<TextServer::TextOverrunFlag> overrun_flags = TextServer::OVERRUN_NO_TRIM;
+				switch (overrun_behavior) {
+					case TextServer::OVERRUN_TRIM_WORD_ELLIPSIS:
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM_WORD_ONLY);
+						overrun_flags.set_flag(TextServer::OVERRUN_ADD_ELLIPSIS);
+						break;
+					case TextServer::OVERRUN_TRIM_ELLIPSIS:
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
+						overrun_flags.set_flag(TextServer::OVERRUN_ADD_ELLIPSIS);
+						break;
+					case TextServer::OVERRUN_TRIM_WORD:
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM_WORD_ONLY);
+						break;
+					case TextServer::OVERRUN_TRIM_CHAR:
+						overrun_flags.set_flag(TextServer::OVERRUN_TRIM);
+						break;
+					case TextServer::OVERRUN_NO_TRIMMING:
+						break;
+				}
 
-		// Fill after min_size calculation.
+				// Fill after min_size calculation.
 
-		int visible_lines = lines_rid.size();
-		if (max_lines_visible >= 0 && visible_lines > max_lines_visible) {
-			visible_lines = max_lines_visible;
-		}
-		if (autowrap_mode != TextServer::AUTOWRAP_OFF) {
-			bool lines_hidden = visible_lines > 0 && visible_lines < lines_rid.size();
-			if (lines_hidden) {
-				overrun_flags.set_flag(TextServer::OVERRUN_ENFORCE_ELLIPSIS);
-			}
-			if (horizontal_alignment == HORIZONTAL_ALIGNMENT_FILL) {
-				for (int i = 0; i < lines_rid.size(); i++) {
-					if (i < visible_lines - 1 || lines_rid.size() == 1) {
-						TS->shaped_text_fit_to_width(lines_rid[i], width);
-					} else if (i == (visible_lines - 1)) {
+				int visible_lines = lines_rid.size();
+				if (max_lines_visible >= 0 && visible_lines > max_lines_visible) {
+					visible_lines = max_lines_visible;
+				}
+				if (autowrap_mode != TextServer::AUTOWRAP_OFF) {
+					bool lines_hidden = visible_lines > 0 && visible_lines < lines_rid.size();
+					if (lines_hidden) {
+						overrun_flags.set_flag(TextServer::OVERRUN_ENFORCE_ELLIPSIS);
+					}
+					if (horizontal_alignment == HORIZONTAL_ALIGNMENT_FILL) {
+						for (int i = 0; i < lines_rid.size(); i++) {
+							if (i < visible_lines - 1 || lines_rid.size() == 1) {
+								TS->shaped_text_fit_to_width(lines_rid[i], width);
+							} else if (i == (visible_lines - 1)) {
+								TS->shaped_text_overrun_trim_to_width(lines_rid[visible_lines - 1], width, overrun_flags);
+							}
+						}
+					} else if (lines_hidden) {
 						TS->shaped_text_overrun_trim_to_width(lines_rid[visible_lines - 1], width, overrun_flags);
 					}
-				}
-			} else if (lines_hidden) {
-				TS->shaped_text_overrun_trim_to_width(lines_rid[visible_lines - 1], width, overrun_flags);
-			}
-		} else {
-			// Autowrap disabled.
-			for (int i = 0; i < lines_rid.size(); i++) {
-				if (horizontal_alignment == HORIZONTAL_ALIGNMENT_FILL) {
-					TS->shaped_text_fit_to_width(lines_rid[i], width);
-					overrun_flags.set_flag(TextServer::OVERRUN_JUSTIFICATION_AWARE);
-					TS->shaped_text_overrun_trim_to_width(lines_rid[i], width, overrun_flags);
-					TS->shaped_text_fit_to_width(lines_rid[i], width, TextServer::JUSTIFICATION_WORD_BOUND | TextServer::JUSTIFICATION_KASHIDA | TextServer::JUSTIFICATION_CONSTRAIN_ELLIPSIS);
 				} else {
-					TS->shaped_text_overrun_trim_to_width(lines_rid[i], width, overrun_flags);
+					// Autowrap disabled.
+					for (int i = 0; i < lines_rid.size(); i++) {
+						if (horizontal_alignment == HORIZONTAL_ALIGNMENT_FILL) {
+							TS->shaped_text_fit_to_width(lines_rid[i], width);
+							overrun_flags.set_flag(TextServer::OVERRUN_JUSTIFICATION_AWARE);
+							TS->shaped_text_overrun_trim_to_width(lines_rid[i], width, overrun_flags);
+							TS->shaped_text_fit_to_width(lines_rid[i], width, TextServer::JUSTIFICATION_WORD_BOUND | TextServer::JUSTIFICATION_KASHIDA | TextServer::JUSTIFICATION_CONSTRAIN_ELLIPSIS);
+						} else {
+							TS->shaped_text_overrun_trim_to_width(lines_rid[i], width, overrun_flags);
+						}
+					}
+				}
+
+				int last_line = MIN(lines_rid.size(), visible_lines + lines_skipped);
+				int line_spacing = settings.is_valid() ? settings->get_line_spacing() : theme_cache.line_spacing;
+				for (int64_t i = lines_skipped; i < last_line; i++) {
+					minsize.height += TS->shaped_text_get_size(lines_rid[i]).y + line_spacing;
 				}
-			}
-		}
 
-		int last_line = MIN(lines_rid.size(), visible_lines + lines_skipped);
-		int line_spacing = settings.is_valid() ? settings->get_line_spacing() : theme_cache.line_spacing;
-		for (int64_t i = lines_skipped; i < last_line; i++) {
-			minsize.height += TS->shaped_text_get_size(lines_rid[i]).y + line_spacing;
+				lines_dirty = false;
+			}
+		} else {
+			callable_mp(this, &Label::_shape).call_deferred();
 		}
+	}
 
-		lines_dirty = false;
+	if (draw_pending) {
+		queue_redraw();
+		draw_pending = false;
 	}
 
-	if (minsize != prev_minsize || font_was_dirty) {
+	if (minsize != prev_minsize) {
 		update_minimum_size();
 	}
 
-	if (!width_stabilized) {
-		callable_mp(this, &Label::_shape).call_deferred();
-	}
+	return can_process_lines;
 }
 
 inline void draw_glyph(const Glyph &p_gl, const RID &p_canvas, const Color &p_font_color, const Vector2 &p_ofs) {
@@ -367,10 +373,9 @@ void Label::_notification(int p_what) {
 			}
 
 			if (dirty || font_dirty || lines_dirty) {
-				_shape();
-				if (lines_dirty) {
+				if (!_shape()) {
 					// There will be another pass.
-					queue_redraw();
+					draw_pending = true;
 					break;
 				}
 			}
@@ -396,7 +401,7 @@ void Label::_notification(int p_what) {
 			style->draw(ci, Rect2(Point2(0, 0), get_size()));
 
 			float total_h = 0.0;
-			int visible_lines = 0;
+			int lines_visible = 0;
 
 			// Get number of lines to fit to the height.
 			for (int64_t i = lines_skipped; i < lines_rid.size(); i++) {
@@ -404,14 +409,14 @@ void Label::_notification(int p_what) {
 				if (total_h > (get_size().height - style->get_minimum_size().height + line_spacing)) {
 					break;
 				}
-				visible_lines++;
+				lines_visible++;
 			}
 
-			if (max_lines_visible >= 0 && visible_lines > max_lines_visible) {
-				visible_lines = max_lines_visible;
+			if (max_lines_visible >= 0 && lines_visible > max_lines_visible) {
+				lines_visible = max_lines_visible;
 			}
 
-			int last_line = MIN(lines_rid.size(), visible_lines + lines_skipped);
+			int last_line = MIN(lines_rid.size(), lines_visible + lines_skipped);
 			bool trim_chars = (visible_chars >= 0) && (visible_chars_behavior == TextServer::VC_CHARS_AFTER_SHAPING);
 			bool trim_glyphs_ltr = (visible_chars >= 0) && ((visible_chars_behavior == TextServer::VC_GLYPHS_LTR) || ((visible_chars_behavior == TextServer::VC_GLYPHS_AUTO) && !rtl_layout));
 			bool trim_glyphs_rtl = (visible_chars >= 0) && ((visible_chars_behavior == TextServer::VC_GLYPHS_RTL) || ((visible_chars_behavior == TextServer::VC_GLYPHS_AUTO) && rtl_layout));
@@ -428,7 +433,7 @@ void Label::_notification(int p_what) {
 			total_h += style->get_margin(SIDE_TOP) + style->get_margin(SIDE_BOTTOM);
 
 			int vbegin = 0, vsep = 0;
-			if (visible_lines > 0) {
+			if (lines_visible > 0) {
 				switch (vertical_alignment) {
 					case VERTICAL_ALIGNMENT_TOP: {
 						// Nothing.
@@ -445,8 +450,8 @@ void Label::_notification(int p_what) {
 					} break;
 					case VERTICAL_ALIGNMENT_FILL: {
 						vbegin = 0;
-						if (visible_lines > 1) {
-							vsep = (size.y - (total_h - line_spacing)) / (visible_lines - 1);
+						if (lines_visible > 1) {
+							vsep = (size.y - (total_h - line_spacing)) / (lines_visible - 1);
 						} else {
 							vsep = 0;
 						}
@@ -615,6 +620,8 @@ void Label::_notification(int p_what) {
 				}
 				ofs.y += TS->shaped_text_get_descent(lines_rid[i]) + vsep + line_spacing;
 			}
+
+			draw_pending = false;
 		} break;
 
 		case NOTIFICATION_THEME_CHANGED: {
@@ -666,25 +673,25 @@ int Label::get_line_count() const {
 int Label::get_visible_line_count() const {
 	Ref<StyleBox> style = theme_cache.normal_style;
 	int line_spacing = settings.is_valid() ? settings->get_line_spacing() : theme_cache.line_spacing;
-	int visible_lines = 0;
+	int lines_visible = 0;
 	float total_h = 0.0;
 	for (int64_t i = lines_skipped; i < lines_rid.size(); i++) {
 		total_h += TS->shaped_text_get_size(lines_rid[i]).y + line_spacing;
 		if (total_h > (get_size().height - style->get_minimum_size().height + line_spacing)) {
 			break;
 		}
-		visible_lines++;
+		lines_visible++;
 	}
 
-	if (visible_lines > lines_rid.size()) {
-		visible_lines = lines_rid.size();
+	if (lines_visible > lines_rid.size()) {
+		lines_visible = lines_rid.size();
 	}
 
-	if (max_lines_visible >= 0 && visible_lines > max_lines_visible) {
-		visible_lines = max_lines_visible;
+	if (max_lines_visible >= 0 && lines_visible > max_lines_visible) {
+		lines_visible = max_lines_visible;
 	}
 
-	return visible_lines;
+	return lines_visible;
 }
 
 void Label::set_horizontal_alignment(HorizontalAlignment p_alignment) {
@@ -969,7 +976,7 @@ void Label::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_visible_ratio"), &Label::get_visible_ratio);
 	ClassDB::bind_method(D_METHOD("set_lines_skipped", "lines_skipped"), &Label::set_lines_skipped);
 	ClassDB::bind_method(D_METHOD("get_lines_skipped"), &Label::get_lines_skipped);
-	ClassDB::bind_method(D_METHOD("set_max_lines_visible", "visible_lines"), &Label::set_max_lines_visible);
+	ClassDB::bind_method(D_METHOD("set_max_lines_visible", "lines_visible"), &Label::set_max_lines_visible);
 	ClassDB::bind_method(D_METHOD("get_max_lines_visible"), &Label::get_max_lines_visible);
 	ClassDB::bind_method(D_METHOD("set_structured_text_bidi_override", "parser"), &Label::set_structured_text_bidi_override);
 	ClassDB::bind_method(D_METHOD("get_structured_text_bidi_override"), &Label::get_structured_text_bidi_override);
diff --git a/scene/gui/label.h b/scene/gui/label.h
index 448cb245eb..36b85f7af8 100644
--- a/scene/gui/label.h
+++ b/scene/gui/label.h
@@ -50,7 +50,6 @@ private:
 	bool uppercase = false;
 
 	bool lines_dirty = true;
-
 	bool dirty = true;
 	bool font_dirty = true;
 	RID text_rid;
@@ -66,6 +65,7 @@ private:
 	float visible_ratio = 1.0;
 	int lines_skipped = 0;
 	int max_lines_visible = -1;
+	bool draw_pending = false;
 
 	Ref<LabelSettings> settings;
 
@@ -83,7 +83,7 @@ private:
 		int font_shadow_outline_size;
 	} theme_cache;
 
-	void _shape();
+	bool _shape();
 	void _invalidate();
 
 protected: