Editor 2D: Change pixel alignment strategy, fix jittering in high zoom

Alignment of scene pixels on screen pixel ensure a crisp rendering of small features (such as text). Unfortunately, alignment of top left pixel on screen adds a lot of jittering when zooming at high zoom factor.

This change allow to snap the top left scene pixel on the closest screen pixel (not only the top-left most), and we do so only when the scale factor is an integer.

1 files changed, 14 insertions, 4 deletions

diff --git a/editor/plugins/canvas_item_editor_plugin.cpp b/editor/plugins/canvas_item_editor_plugin.cpp
index 6e1166bb37..9f66672f4a 100644
--- a/editor/plugins/canvas_item_editor_plugin.cpp
+++ b/editor/plugins/canvas_item_editor_plugin.cpp
@@ -4306,10 +4306,20 @@ void CanvasItemEditor::_zoom_on_position(float p_zoom, Point2 p_position) {
 
 	float prev_zoom = zoom;
 	zoom = p_zoom;
-	Point2 ofs = p_position;
-	ofs = ofs / prev_zoom - ofs / zoom;
-	view_offset.x = Math::round(view_offset.x + ofs.x);
-	view_offset.y = Math::round(view_offset.y + ofs.y);
+
+	view_offset += p_position / prev_zoom - p_position / zoom;
+
+	// We want to align in-scene pixels to screen pixels, this prevents blurry rendering
+	// in small details (texts, lines).
+	// This correction adds a jitter movement when zooming, so we correct only when the
+	// zoom factor is an integer. (in the other cases, all pixels won't be aligned anyway)
+	float closest_zoom_factor = Math::round(zoom);
+	if (Math::is_zero_approx(zoom - closest_zoom_factor)) {
+		// make sure scene pixel at view_offset is aligned on a screen pixel
+		Vector2 view_offset_int = view_offset.floor();
+		Vector2 view_offset_frac = view_offset - view_offset_int;
+		view_offset = view_offset_int + (view_offset_frac * closest_zoom_factor).round() / closest_zoom_factor;
+	}
 
 	_update_zoom_label();
 	update_viewport();