Shapes: flipped shapes keep their text readable (#35)

Flips mirror a shape's geometry, never its text. The text was drawn with the shape's full
transform, so every label on a flipped arrow came out mirrored (flipH) or mirrored upside down
(flipV). As in PowerPoint, the text rect keeps its flipped place and the text is mirrored back
about the rect's centre: flipH text stays upright, flipV (or both flips) turns it 180°, rotation
still applies, and the same holds for shapes inside flipped groups.

render::text_transform is that transform (plus vertical-text rotation). Drawing, the PDF text
layer and link boxes, morph text, the editing caret and selection, and click-to-place-the-caret
all use it, so a click lands on the character drawn under it.

Co-authored-by: lloyd <lloyd@stackworx.io>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

crates/engine/src/tests.rs

@@ -426,6 +426,27 @@ fn right_to_left_paragraphs() {
     assert_eq!(para(&s).rtl, Some(true));
 }
 
+#[test]
+fn clicks_in_flipped_shapes_hit_the_text_where_it_is_drawn() {
+    // Flips don't mirror text, so a click lands on the character drawn under it.
+    let mut s = session();
+    let r = s.execute("shape.insert", &json!({"preset": "rect", "rect": [100, 100, 400, 100], "text": "Hello flipped world"})).unwrap();
+    let id = deckcraft_model::ShapeId(r["id"].as_u64().unwrap() as u32);
+    let pos = |s: &Session, x: f64, y: f64| {
+        let st = s.doc().unwrap();
+        tools::text_pos(st, st.shape(id).unwrap(), deckcraft_geom::Point::new(x, y))
+    };
+    let xs = [240.0, 300.0, 360.0];
+    let plain = xs.map(|x| pos(&s, x, 150.0));
+    assert!(plain[0].1 < plain[1].1 && plain[1].1 < plain[2].1, "{plain:?}");
+    s.execute("shape.flip", &json!({"axis": "horizontal"})).unwrap();
+    assert_eq!(xs.map(|x| pos(&s, x, 150.0)), plain);
+    // flipV turns the text 180° about the box centre (300, 150).
+    s.execute("shape.flip", &json!({"axis": "horizontal"})).unwrap();
+    s.execute("shape.flip", &json!({"axis": "vertical"})).unwrap();
+    assert_eq!(xs.map(|x| pos(&s, 600.0 - x, 150.0)), plain);
+}
+
 #[test]
 fn inserted_hyperlinks_look_like_links() {
     let mut s = session();

crates/engine/src/tools.rs

@@ -1258,10 +1258,12 @@ fn hit_shape(st: &crate::DocState, sh: &Shape, p: Point, tol: f64) -> Option<Hit
 /// Text position under slide point `p` in shape `sh`.
 pub fn text_pos(st: &crate::DocState, sh: &Shape, p: Point) -> (usize, usize) {
     let x = xfrm_of(&st.doc, &st.selection, sh);
-    let local = x.affine().inverse() * p;
     let t = TextSel { shape: sh.id, ..Default::default() };
     match cmd::text::layout_for(st, &t) {
         Some(l) => {
+            // The text's own transform: flips don't mirror text, vertical text is turned.
+            let tr = deckcraft_render::shape_geometry(sh, x.w, x.h).text_rect;
+            let local = deckcraft_render::text_transform(x.affine(), tr, l.rotation).inverse() * p;
             let h = l.hit(local);
             (h.para, h.ch)
         }