Portrait and square screens: world pixels, interface and zoom count on the shorter side

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -973,7 +973,12 @@ async fn main() {
         // 900 rows (360 -> 1080), on a desktop and on a touch screen alike (a phone has about
         // 1080 device rows in landscape; a smaller screen draws in device pixels)
         let need: u32 = 900;
-        ui::set_virtual_rows(rows * need.div_ceil(rows));
+        // measured on the shorter side: upright (portrait) the width gets those pixels and the
+        // height grows with the screen, so the world and the menus keep their size
+        let short = rows * need.div_ceil(rows);
+        let (w, h) = (screen_width().max(1.0), screen_height().max(1.0));
+        let vrows = if h > w { (short as f32 * h / w).round() as u32 } else { short };
+        ui::set_virtual_rows(vrows);
         if touch_mode {
             // the pointer is the finger, or the position of this frame's gesture
             let gpos = gestures.iter().rev().find_map(|g| match *g {