From d365b60704c1a7eec989fe760917e01bdd0c9fe3 Mon Sep 17 00:00:00 2001
From: aldozar <azarate@azf.com.mx>
Date: Mon, 12 Oct 2026 01:21:18 -0600
Subject: [PATCH] MIRROR and PASTE previews on the GPU; GPU previews in layouts
 too (#655)

Squash of PR #655 by @aldozar.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/engine/src/cmd/edit.rs   |  6 +++++
 crates/engine/src/cmd/modify.rs | 46 ++++++++++++++++++++++++++++++---
 crates/engine/src/prompt.rs     |  5 +++-
 crates/engine/src/tests.rs      | 27 ++++++++++++++++---
 crates/ui-egui/src/canvas.rs    | 31 ++++++++++++++++------
 5 files changed, 99 insertions(+), 16 deletions(-)

diff --git a/crates/engine/src/cmd/edit.rs b/crates/engine/src/cmd/edit.rs
index dfef8a75..822ef876 100644
--- a/crates/engine/src/cmd/edit.rs
+++ b/crates/engine/src/cmd/edit.rs
@@ -609,6 +609,12 @@ impl Interactive for PasteM {
             _ => Ok(Step::Continue),
         }
     }
+    fn drag(&self, s: &Session, c: Vec2) -> Option<crate::prompt::Drag> {
+        if self.mode == PasteMode::Orig || s.clipboard.is_empty() {
+            return None;
+        }
+        Some(crate::prompt::Drag { handles: Vec::new(), matrix: Mat3::translate(c - s.clipboard_base), extra: Vec::new(), clipboard: true })
+    }
     fn preview(&self, s: &Session, c: Vec2) -> Vec<cadcraft_doc::EntityKind> {
         let m = Mat3::translate(c - s.clipboard_base);
         s.clipboard
diff --git a/crates/engine/src/cmd/modify.rs b/crates/engine/src/cmd/modify.rs
index 122365ed..e087fb22 100644
--- a/crates/engine/src/cmd/modify.rs
+++ b/crates/engine/src/cmd/modify.rs
@@ -1712,6 +1712,26 @@ impl SelectThen {
     }
 }
 
+/// Objects whose text MIRROR keeps readable instead of mirroring it with the geometry.
+fn keeps_reading_when_mirrored(k: &EntityKind) -> bool {
+    match k {
+        EntityKind::Insert(i) => !i.attribs.is_empty(),
+        k => matches!(
+            k,
+            EntityKind::Text(_)
+                | EntityKind::AttDef(_)
+                | EntityKind::MText(_)
+                | EntityKind::Dimension(_)
+                | EntityKind::MLeader(_)
+                | EntityKind::Table(_)
+                | EntityKind::Tolerance(_)
+        ),
+    }
+}
+
+/// Text objects transformed for each frame of a MIRROR preview (on the CPU); more are not drawn.
+const MAX_MIRROR_TEXT_PREVIEW: usize = 1000;
+
 /// A finite length greater than zero (rejects 0, negatives, NaN and infinity).
 fn positive_length(v: Option<f64>) -> Option<f64> {
     v.filter(|f| f.is_finite() && *f > 1e-12)
@@ -1927,8 +1947,7 @@ impl Interactive for SelectThen {
         out.push(line(base, c));
         out
     }
-    fn drag(&self, _s: &Session, c: Vec2) -> Option<crate::prompt::Drag> {
-        // Mirror stays on `preview`: MIRRTEXT keeps text readable, which a plain matrix can't.
+    fn drag(&self, s: &Session, c: Vec2) -> Option<crate::prompt::Drag> {
         if (self.op == Op::Rotate && self.reference) || !self.sel.done {
             return None;
         }
@@ -1938,9 +1957,30 @@ impl Interactive for SelectThen {
             Op::Rotate => Mat3::rotate_about(base, base.angle_to(c)),
             Op::Scale if !self.reference => Mat3::scale_about(base, base.dist(c).max(1e-9)),
             Op::Scale => Mat3::scale_about(base, self.ref_len.and_then(|r| positive_length(Some(base.dist(c) / r)))?),
+            Op::Mirror if !self.ask_erase => Mat3::mirror(base, c),
             _ => return None,
         };
-        Some(crate::prompt::Drag { handles: self.objs.clone(), matrix, extra: vec![line(base, c)] })
+        let mut extra = vec![line(base, c)];
+        if self.op != Op::Mirror {
+            return Some(crate::prompt::Drag { handles: self.objs.clone(), matrix, extra, clipboard: false });
+        }
+        // Mirrored text keeps reading left to right (MIRRTEXT 0), which the matrix alone can't
+        // draw: those objects are transformed one by one, the rest is mirrored on the GPU.
+        let d = s.doc().ok()?;
+        let mut handles = Vec::with_capacity(self.objs.len());
+        let mut texts = 0;
+        for h in &self.objs {
+            let Some(e) = d.entity(*h) else { continue };
+            if !keeps_reading_when_mirrored(&e.kind) {
+                handles.push(*h);
+            } else if texts < MAX_MIRROR_TEXT_PREVIEW {
+                texts += 1;
+                let mut k = e.kind.clone();
+                k.transform(&matrix);
+                extra.push(k);
+            }
+        }
+        Some(crate::prompt::Drag { handles, matrix, extra, clipboard: false })
     }
 }
 
diff --git a/crates/engine/src/prompt.rs b/crates/engine/src/prompt.rs
index a150fbba..180d8f9a 100644
--- a/crates/engine/src/prompt.rs
+++ b/crates/engine/src/prompt.rs
@@ -178,8 +178,11 @@ pub trait Interactive: Send {
 pub struct Drag {
     pub handles: Vec<Handle>,
     pub matrix: Mat3,
-    /// Rubber-band geometry drawn as well (the base-to-cursor line).
+    /// Rubber-band geometry drawn as well (the base-to-cursor line), and dragged objects the
+    /// matrix can't draw (text MIRROR keeps readable), already transformed.
     pub extra: Vec<EntityKind>,
+    /// The dragged objects are the clipboard's ([`Session::clipboard`]), not `handles`.
+    pub clipboard: bool,
 }
 
 /// Parse a typed point: `x,y[,z]`, `@dx,dy`, `@dist<angle`, `dist<angle`, `#x,y` (absolute),
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 1e231206..889ae10c 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -361,10 +361,29 @@ fn copy_and_rotate_drag_as_a_transform_of_the_selection() {
     let (d, _) = start("rotate").drag(Vec2::new(0.0, 5.0)).expect("ROTATE drags its selection");
     assert!(d.matrix.apply(Vec2::new(1.0, 0.0)).near(Vec2::new(0.0, 1.0), 1e-9));
 
-    // MIRROR keeps the per-entity preview (MIRRTEXT).
-    let s = start("mirror");
-    assert!(s.drag(Vec2::new(0.0, 5.0)).is_none());
-    assert!(!s.preview(Vec2::new(0.0, 5.0)).is_empty());
+    // MIRROR: geometry is mirrored by the matrix; text, which stays readable, is transformed
+    // object by object and comes with the extra geometry.
+    let mut s = Session::new();
+    s.execute("line", &json!({"points": [[0, 0], [1, 0]]})).unwrap();
+    s.execute("text", &json!({"at": [2, 2], "height": 1, "text": "A"})).unwrap();
+    for t in ["mirror", "all", "", "0,0"] {
+        s.cmdline(t).unwrap();
+    }
+    let (d, extra) = s.drag(Vec2::new(0.0, 5.0)).expect("MIRROR drags its selection");
+    assert_eq!(d.handles.len(), 1, "the line is mirrored by the matrix");
+    assert!(d.matrix.apply(Vec2::new(1.0, 0.0)).near(Vec2::new(-1.0, 0.0), 1e-9));
+    assert_eq!(extra.len(), 2, "the base-to-cursor line and the text");
+    let EntityKind::Text(t) = &extra[1].kind else { panic!("expected the text") };
+    assert!(t.insert.xy().near(Vec2::new(-2.0, 2.0), 1e-9) && t.rotation.abs() < 1e-9, "mirrored, still reading left to right");
+
+    // PASTECLIP drags the clipboard.
+    let mut s = Session::new();
+    let l = s.execute("line", &json!({"points": [[0, 0], [1, 0]]})).unwrap();
+    s.execute("copyclip", &json!({"handles": [l["handles"][0].clone()]})).unwrap();
+    s.cmdline("pasteclip").unwrap();
+    let (d, _) = s.drag(Vec2::new(5.0, 5.0)).expect("PASTECLIP drags the clipboard");
+    assert!(d.clipboard && d.handles.is_empty());
+    assert!(d.matrix.apply(s.clipboard_base).near(Vec2::new(5.0, 5.0), 1e-9));
 }
 
 #[test]
diff --git a/crates/ui-egui/src/canvas.rs b/crates/ui-egui/src/canvas.rs
index 6faeb6a7..027c681b 100644
--- a/crates/ui-egui/src/canvas.rs
+++ b/crates/ui-egui/src/canvas.rs
@@ -426,22 +426,35 @@ fn draw_highlight_gpu(
 /// zoom band changes), and each frame only the transform in the view uniform moves. Rebuilding
 /// the transformed copies as egui shapes every frame was slow with heavy selections and could
 /// overflow the GPU buffer limit.
-fn draw_drag_gpu(c: &mut CanvasState, p: &egui::Painter, xf: &Xf, doc: &cadcraft_doc::Drawing, drag: &cadcraft_engine::Drag, bg: Rgb) {
+/// `clipboard` is the session's clipboard and its serial (dragged when `drag.clipboard`, by PASTE).
+fn draw_drag_gpu(
+    c: &mut CanvasState,
+    p: &egui::Painter,
+    xf: &Xf,
+    doc: &cadcraft_doc::Drawing,
+    drag: &cadcraft_engine::Drag,
+    clipboard: (&[cadcraft_doc::Entity], u64),
+    bg: Rgb,
+) {
     // Tessellate for a power-of-two zoom band so zooming mid-drag rebuilds only every 2x.
     let band = xf.scale.max(1e-300).log2().round() as i32;
     let key = {
         use std::hash::{Hash, Hasher};
         let mut h = std::collections::hash_map::DefaultHasher::new();
         (c.key, band, bg.0, bg.1, bg.2, &drag.handles).hash(&mut h);
+        if drag.clipboard {
+            clipboard.1.hash(&mut h);
+        }
         h.finish()
     };
     if c.drag_key != Some(key) {
         let band_scale = 2f64.powi(band);
-        let list = cadcraft_render::build_entities(
-            doc,
-            drag.handles.iter().filter_map(|h| doc.entity(*h)).map(|e| e.as_ref()),
-            &cadcraft_render::Options { tolerance: 0.5 / band_scale, min_dash: 2.0 / band_scale, ..Default::default() },
-        );
+        let opts = cadcraft_render::Options { tolerance: 0.5 / band_scale, min_dash: 2.0 / band_scale, ..Default::default() };
+        let list = if drag.clipboard {
+            cadcraft_render::build_entities(doc, clipboard.0.iter(), &opts)
+        } else {
+            cadcraft_render::build_entities(doc, drag.handles.iter().filter_map(|h| doc.entity(*h)).map(|e| e.as_ref()), &opts)
+        };
         let origin = if list.bounds.is_empty() { Vec2::ZERO } else { list.bounds.center() };
         let mesh = crate::gpu::build_mesh(&list, origin, bg, false);
         if let Ok(mut slot) = c.drag_slot.lock() {
@@ -1174,13 +1187,15 @@ pub fn show(app: &mut CadApp, ui: &mut egui::Ui) {
         }
     }
     // Rubber band preview of the active command.
-    let drag = match (app.canvas.cursor, app.canvas.gpu.is_some() && sheet.is_none()) {
+    // `xf` is the space being edited: paper space, or model space inside the active viewport.
+    let drag = match (app.canvas.cursor, app.canvas.gpu.is_some()) {
         (Some(c), true) => app.session.drag(c),
         _ => None,
     };
     if let Some((drag, extra)) = drag {
         if let Ok(st) = app.session.state() {
-            draw_drag_gpu(&mut app.canvas, &painter, &xf, &st.doc, &drag, bg);
+            let serial = app.session.clipboard_source.as_ref().map_or(0, |c| c.serial);
+            draw_drag_gpu(&mut app.canvas, &painter, &xf, &st.doc, &drag, (&app.session.clipboard, serial), bg);
             let list = cadcraft_render::build_entities(
                 &st.doc,
                 extra.iter(),