From 9b2843f14f87b27cb3ca749ca1e1c5d920042b6f Mon Sep 17 00:00:00 2001
From: bruvzg <7645683+bruvzg@users.noreply.github.com>
Date: Fri, 13 Jan 2023 10:30:12 +0200
Subject: [PATCH] Improve dashed line alignment and make it optional.

---
 doc/classes/CanvasItem.xml |  1 +
 scene/main/canvas_item.cpp | 22 ++++++++++++++--------
 scene/main/canvas_item.h   |  2 +-
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/doc/classes/CanvasItem.xml b/doc/classes/CanvasItem.xml
index 5171e0acbeb9..fbab1d76a09b 100644
--- a/doc/classes/CanvasItem.xml
+++ b/doc/classes/CanvasItem.xml
@@ -97,6 +97,7 @@
 			<param index="2" name="color" type="Color" />
 			<param index="3" name="width" type="float" default="1.0" />
 			<param index="4" name="dash" type="float" default="2.0" />
+			<param index="5" name="aligned" type="bool" default="true" />
 			<description>
 				Draws a dashed line from a 2D point to another, with a given color and width. See also [method draw_multiline] and [method draw_polyline].
 			</description>
diff --git a/scene/main/canvas_item.cpp b/scene/main/canvas_item.cpp
index 3f98b540fc05..05caad78a0d3 100644
--- a/scene/main/canvas_item.cpp
+++ b/scene/main/canvas_item.cpp
@@ -483,7 +483,7 @@ bool CanvasItem::is_y_sort_enabled() const {
 	return y_sort_enabled;
 }
 
-void CanvasItem::draw_dashed_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width, real_t p_dash) {
+void CanvasItem::draw_dashed_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width, real_t p_dash, bool p_aligned) {
 	ERR_FAIL_COND_MSG(!drawing, "Drawing is only allowed inside NOTIFICATION_DRAW, _draw() function or 'draw' signal.");
 
 	float length = (p_to - p_from).length();
@@ -492,14 +492,20 @@ void CanvasItem::draw_dashed_line(const Point2 &p_from, const Point2 &p_to, cons
 		return;
 	}
 
-	Point2 off = p_from;
 	Vector2 step = p_dash * (p_to - p_from).normalized();
-	int steps = length / p_dash / 2;
-	for (int i = 0; i < steps; i++) {
-		RenderingServer::get_singleton()->canvas_item_add_line(canvas_item, off, (off + step), p_color, p_width);
-		off += 2 * step;
+	int steps = (p_aligned) ? Math::ceil(length / p_dash) : Math::floor(length / p_dash);
+	if (steps % 2 == 0) {
+		steps--;
+	}
+
+	Point2 off = p_from;
+	if (p_aligned) {
+		off += (p_to - p_from).normalized() * (length - steps * p_dash) / 2.0;
+	}
+	for (int i = 0; i < steps; i += 2) {
+		RenderingServer::get_singleton()->canvas_item_add_line(canvas_item, (i == 0) ? p_from : off, (p_aligned && i == steps - 1) ? p_to : (off + step), p_color, p_width);
+		off += step * 2;
 	}
-	RenderingServer::get_singleton()->canvas_item_add_line(canvas_item, off, p_to, p_color, p_width);
 }
 
 void CanvasItem::draw_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width, bool p_antialiased) {
@@ -963,7 +969,7 @@ void CanvasItem::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("is_draw_behind_parent_enabled"), &CanvasItem::is_draw_behind_parent_enabled);
 
 	ClassDB::bind_method(D_METHOD("draw_line", "from", "to", "color", "width", "antialiased"), &CanvasItem::draw_line, DEFVAL(1.0), DEFVAL(false));
-	ClassDB::bind_method(D_METHOD("draw_dashed_line", "from", "to", "color", "width", "dash"), &CanvasItem::draw_dashed_line, DEFVAL(1.0), DEFVAL(2.0));
+	ClassDB::bind_method(D_METHOD("draw_dashed_line", "from", "to", "color", "width", "dash", "aligned"), &CanvasItem::draw_dashed_line, DEFVAL(1.0), DEFVAL(2.0), DEFVAL(true));
 	ClassDB::bind_method(D_METHOD("draw_polyline", "points", "color", "width", "antialiased"), &CanvasItem::draw_polyline, DEFVAL(1.0), DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("draw_polyline_colors", "points", "colors", "width", "antialiased"), &CanvasItem::draw_polyline_colors, DEFVAL(1.0), DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("draw_arc", "center", "radius", "start_angle", "end_angle", "point_count", "color", "width", "antialiased"), &CanvasItem::draw_arc, DEFVAL(1.0), DEFVAL(false));
diff --git a/scene/main/canvas_item.h b/scene/main/canvas_item.h
index 47b40c9b463e..62357a183403 100644
--- a/scene/main/canvas_item.h
+++ b/scene/main/canvas_item.h
@@ -247,7 +247,7 @@ class CanvasItem : public Node {
 
 	/* DRAWING API */
 
-	void draw_dashed_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width = 1.0, real_t p_dash = 2.0);
+	void draw_dashed_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width = 1.0, real_t p_dash = 2.0, bool p_aligned = true);
 	void draw_line(const Point2 &p_from, const Point2 &p_to, const Color &p_color, real_t p_width = 1.0, bool p_antialiased = false);
 	void draw_polyline(const Vector<Point2> &p_points, const Color &p_color, real_t p_width = 1.0, bool p_antialiased = false);
 	void draw_polyline_colors(const Vector<Point2> &p_points, const Vector<Color> &p_colors, real_t p_width = 1.0, bool p_antialiased = false);