fix(text): grip-drag no longer hides text (#316)

Dragging text by a grip hid it until release. The dragged entity is
hidden from the base wire set and shown as a preview overlay, but its
SDF glyph quads (text_verts) were never uploaded for the preview, so
the text vanished mid-drag.

Add a per-frame preview_text GPU buffer (sibling to preview_wires). A
rigid whole-entity move of pure text (TEXT/MTEXT, Square insertion grip)
slides the drag-start glyphs by the drag delta instead of re-shaping the
run every move; reshape grips (MTEXT width), dimensions and wire
entities re-tessellate and feed the same buffer.

Also fold preview_text into render_signature: a pure-text slide leaves
preview_wires empty, so without it the scene-render cache froze the
dragged text at its first frame (grip moved but text stayed, then
jumped to place on release).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -377,6 +377,15 @@ pub(super) struct OpenCADStudio {
     /// the document live (so grips / properties track), so cancel reverts from
     /// this backup. Dropped (kept) on a normal commit.
     grip_original: Option<acadrust::EntityType>,
+    /// Drag-start snapshot of the dragged entity's SDF glyph quads. A whole-
+    /// entity text move slides these each frame (translating the already-shaped
+    /// glyphs) instead of re-tessellating the run every cursor move (issue #316).
+    grip_text_verts: Vec<crate::scene::pipeline::text_gpu::TextVertex>,
+    /// True when the current grip drag is a rigid whole-entity move of pure text
+    /// (TEXT / MTEXT, no wire geometry, insertion grip) — the case where the
+    /// glyphs can just be slid. A reshape grip (e.g. an MTEXT width handle) or an
+    /// entity with wires re-tessellates instead so the preview stays exact.
+    grip_text_slide: bool,
     /// Open Quick Select panel state. `None` = panel closed. Filters are
     /// applied via `Message::QSelectApply`; the panel is dismissed on
     /// Apply / Cancel / Esc / outside-click.
@@ -2101,6 +2110,8 @@ impl OpenCADStudio {
             grip_preview_handle: None,
             hover_dwell: None,
             grip_original: None,
+            grip_text_verts: Vec::new(),
+            grip_text_slide: false,
             qselect: None,
             show_ucs_icon: true,
             ucs_icon_at_origin: true,

src/app/update/command.rs

@@ -493,6 +493,8 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                     // once, and drop the preview.
                     if let Some(h) = self.grip_preview_handle.take() {
                         let i = self.active_tab;
+                        self.grip_text_verts = Vec::new();
+                        self.grip_text_slide = false;
                         if let Some(orig) = self.grip_original.take() {
                             if let Some(e) = self.tabs[i].scene.document.get_entity_mut(h) {
                                 *e = orig;

src/app/update/viewport.rs

@@ -721,6 +721,25 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                         // block cache so the hide doesn't re-tessellate blocks.
                         self.tabs[i].scene.bump_geometry_no_blocks();
                         self.grip_preview_handle = Some(grip.handle);
+                        // Snapshot the entity's glyph quads once so each move can
+                        // slide the already-shaped text rather than re-shaping it
+                        // (issue #316). The fast slide path only runs for a rigid
+                        // whole-entity move of pure text: no wire geometry (so a
+                        // dimension re-tessellates) and a Square insertion grip (so
+                        // an MTEXT width handle, a Triangle, still re-tessellates so
+                        // the re-wrap is exact).
+                        let snap = self.tabs[i].scene.wire_models_for(&[grip.handle]);
+                        self.grip_text_verts =
+                            snap.iter().flat_map(|w| w.text_verts.iter().copied()).collect();
+                        let square_grip = self.tabs[i]
+                            .selected_grips
+                            .iter()
+                            .find(|g| g.id == grip.grip_id)
+                            .map(|g| g.shape == crate::scene::model::object::GripShape::Square)
+                            .unwrap_or(false);
+                        self.grip_text_slide = !self.grip_text_verts.is_empty()
+                            && snap.iter().all(|w| w.points.is_empty())
+                            && square_grip;
                     }
 
                     // The edited entity is hidden, so it's already absent from
@@ -778,10 +797,29 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                         .apply_grip(grip.handle, grip.grip_id, apply);
                     self.tabs[i].dirty = true;
                     self.tabs[i].active_grip.as_mut().unwrap().last_world = snapped;
-                    // Overlay the moved entity (hidden from the base) — no base
+                    // Overlay the moved entity (hidden from the base). Pure text
-                    // re-tessellation, just a one-entity preview tessellation.
+                    // moved as a whole slides its drag-start glyphs — no re-shaping
+                    // and no wire re-tess. Anything else (wire geometry, or a point
+                    // grip that reshapes text) is re-tessellated for an exact
+                    // preview; either way the glyphs ride the preview-text buffer
+                    // so dragged text never vanishes mid-drag (issue #316).
+                    if self.grip_text_slide {
+                        let d = snapped - grip.origin_world;
+                        let slid = crate::scene::pipeline::text_gpu::translate_verts(
+                            &self.grip_text_verts,
+                            [d.x, d.y, d.z],
+                        );
+                        self.tabs[i].scene.set_preview_text(slid);
+                        self.tabs[i].scene.set_preview_wires(Vec::new());
+                    } else {
                         let preview = self.tabs[i].scene.wire_models_for(&[grip.handle]);
+                        let ptext = preview
+                            .iter()
+                            .flat_map(|w| w.text_verts.iter().copied())
+                            .collect();
+                        self.tabs[i].scene.set_preview_text(ptext);
                         self.tabs[i].scene.set_preview_wires(preview);
+                    }
                     self.refresh_selected_grips();
                     self.refresh_properties();
                     return Task::none();
@@ -1729,6 +1767,8 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                     // re-tessellate the base once, dropping the overlay preview.
                     if let Some(h) = self.grip_preview_handle.take() {
                         self.grip_original = None;
+                        self.grip_text_verts = Vec::new();
+                        self.grip_text_slide = false;
                         self.tabs[i].scene.hidden.remove(&h);
                         self.tabs[i].scene.clear_preview_wire();
                         // Only the dragged entity changed — re-tessellate just it.

src/scene/entity.rs

@@ -1649,6 +1649,7 @@ impl Scene {
         self.document = CadDocument::new();
         self.selected = HashSet::default();
         self.preview_wires = vec![];
+        self.preview_text = vec![];
         self.current_layout = "Model".to_string();
         self.hatches = HashMap::default();
         self.meshes = HashMap::default();

src/scene/mod.rs

@@ -752,6 +752,10 @@ pub struct Scene {
     pub selection_filter: HashSet<String>,
     /// In-progress preview wires while a command is active (rubber-band + object ghosts).
     pub preview_wires: Vec<WireModel>,
+    /// In-progress preview SDF glyph quads (grip drag / command preview). Rides
+    /// a per-frame GPU buffer separate from the epoch-cached base text so the
+    /// dragged text stays visible while it's hidden from the base set (#316).
+    pub preview_text: Vec<crate::scene::pipeline::text_gpu::TextVertex>,
     /// Committed-segment wire drawn during multi-point commands (normal colour).
     pub interim_wire: Option<WireModel>,
     pub camera_generation: u64,
@@ -995,6 +999,7 @@ impl Scene {
             transparency_display: true,
             selection_filter: HashSet::default(),
             preview_wires: vec![],
+            preview_text: vec![],
             interim_wire: None,
             camera_generation: 0,
             geometry_epoch: GEOMETRY_EPOCH.fetch_add(1, Ordering::Relaxed),

src/scene/pipeline/mod.rs

@@ -90,6 +90,14 @@ pub struct Pipeline {
     /// analogue of the selected-wire xray overlay). Rebuilt on selection change.
     text_highlight_vbuf: Option<wgpu::Buffer>,
     text_highlight_vcount: u32,
+    /// Live grip-drag / command-preview SDF glyph quads. The base text buffer
+    /// only re-uploads on a geometry-epoch change, but a grip drag hides the
+    /// dragged entity from the base wire set and shows it as a per-frame
+    /// overlay — so its glyphs ride here, re-uploaded every frame like
+    /// `gpu_preview_wires`, or the dragged text vanishes until release re-tesses
+    /// it back into the base set (issue #316).
+    text_preview_vbuf: Option<wgpu::Buffer>,
+    text_preview_vcount: u32,
     /// Last requested render size (the full viewport rect, in pixels). The
     /// geometry passes render at this size; the blit UV is scaled by
     /// `depth_texture_size / alloc_size` so it samples only the filled region.
@@ -1161,6 +1169,8 @@ impl Pipeline {
             text_vcount: 0,
             text_highlight_vbuf: None,
             text_highlight_vcount: 0,
+            text_preview_vbuf: None,
+            text_preview_vcount: 0,
             mesh_pipeline,
             mesh_transparent_pipeline,
             mesh_highlight_pipeline,
@@ -1383,6 +1393,39 @@ impl Pipeline {
         };
     }
 
+    /// Upload the live grip-drag / command-preview SDF glyph quads. Re-uploaded
+    /// every frame they're present, kept separate from the epoch-cached base
+    /// text buffer so a drag never re-uploads the (potentially huge) resident
+    /// text set — and so the dragged entity's glyphs (hidden from the base set
+    /// while the drag is live) still reach the GPU each frame (issue #316).
+    pub fn upload_preview_text(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        verts: &[text_gpu::TextVertex],
+    ) {
+        if verts.is_empty() {
+            self.text_preview_vbuf = None;
+            self.text_preview_vcount = 0;
+            return;
+        }
+        // Ensure the glyph atlas exists / is current even when the base text
+        // pass didn't run this frame (e.g. the dragged text is the only text).
+        if let Ok(mut atlas) = crate::scene::text::sdf_atlas::text_atlas().lock() {
+            if self.text_atlas_gpu.is_none() || atlas.is_dirty() {
+                self.text_atlas_gpu = Some(text_gpu::TextAtlasGpu::upload(
+                    device,
+                    queue,
+                    &atlas,
+                    &self.text_atlas_bgl,
+                ));
+                atlas.clear_dirty();
+            }
+        }
+        self.text_preview_vbuf = text_gpu::upload_vertices(device, verts);
+        self.text_preview_vcount = verts.len() as u32;
+    }
+
     /// Recompute pixel scissor rects for viewport-clipped wires from the current view_proj.
     /// Called every frame from prepare() because scissor pixels shift with pan/zoom.
     pub fn compute_wire_scissors(&mut self, view_rot: glam::Mat4, eye: glam::DVec3, clip_w: u32, clip_h: u32) {
@@ -2143,7 +2186,9 @@ impl Pipeline {
         if let Some(atlas) = &self.text_atlas_gpu {
             let have_base = self.text_vbuf.is_some() && self.text_vcount > 0;
             let have_hl = self.text_highlight_vbuf.is_some() && self.text_highlight_vcount > 0;
-            if have_base || have_hl {
+            let have_preview =
+                self.text_preview_vbuf.is_some() && self.text_preview_vcount > 0;
+            if have_base || have_hl || have_preview {
                 let mut pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                     label: Some("text.render_pass"),
                     color_attachments: &[Some(wgpu::RenderPassColorAttachment {
@@ -2182,6 +2227,13 @@ impl Pipeline {
                         pass.draw(0..self.text_highlight_vcount, 0..1);
                     }
                 }
+                // Grip-drag / command-preview glyphs, drawn over the base text.
+                if let Some(pbuf) = &self.text_preview_vbuf {
+                    if self.text_preview_vcount > 0 {
+                        pass.set_vertex_buffer(0, pbuf.slice(..));
+                        pass.draw(0..self.text_preview_vcount, 0..1);
+                    }
+                }
             }
         }
 

src/scene/pipeline/text_gpu.rs

@@ -120,6 +120,29 @@ pub fn push_glyph_vertices(
     }
 }
 
+/// Slide every glyph vertex by a world-space delta, re-splitting the
+/// double-single position. Lets a grip drag move already-shaped text by
+/// translating the drag-start glyphs each frame instead of re-tessellating
+/// (re-shaping) the run on every cursor move (issue #316).
+pub fn translate_verts(verts: &[TextVertex], delta: [f64; 3]) -> Vec<TextVertex> {
+    verts
+        .iter()
+        .map(|v| {
+            let wx = v.pos[0] as f64 + v.pos_low[0] as f64 + delta[0];
+            let wy = v.pos[1] as f64 + v.pos_low[1] as f64 + delta[1];
+            let wz = v.pos[2] as f64 + v.pos_low[2] as f64 + delta[2];
+            let (xh, xl) = split_ds(wx);
+            let (yh, yl) = split_ds(wy);
+            let (zh, zl) = split_ds(wz);
+            TextVertex {
+                pos: [xh, yh, zh],
+                pos_low: [xl, yl, zl],
+                ..*v
+            }
+        })
+        .collect()
+}
+
 // ── Atlas texture ───────────────────────────────────────────────────────────
 
 /// The shared glyph atlas on the GPU: a single-channel (R8) SDF texture plus

src/scene/preview.rs

@@ -14,11 +14,18 @@ impl Scene {
         self.preview_wires = wires;
     }
 
+    pub fn set_preview_text(&mut self, verts: Vec<crate::scene::pipeline::text_gpu::TextVertex>) {
+        // Overlay glyphs — same reasoning as `set_preview_wires`: no geometry
+        // bump. Uploaded to a dedicated per-frame text buffer in `prepare`.
+        self.preview_text = verts;
+    }
+
     pub fn clear_preview_wire(&mut self) {
         // No geometry bump — see `set_preview_wires`. Dropping the overlay
         // flips the wire content id back to the base tessellation id, which
         // re-uploads the base wires (without the preview) on the next frame.
         self.preview_wires = vec![];
+        self.preview_text = vec![];
         self.interim_wire = None;
     }
 

src/scene/view/render.rs

@@ -41,6 +41,11 @@ pub struct ViewportData {
     pub(in crate::scene) face3d_wires: Arc<Vec<WireModel>>,
     /// SDF text-quad vertices (Phase 2b). Empty unless `OCS_TEXT_SDF` is set.
     pub(in crate::scene) text_verts: Arc<Vec<crate::scene::pipeline::text_gpu::TextVertex>>,
+    /// Live grip-drag / command-preview glyph quads. Kept out of the epoch-cached
+    /// `text_verts` and uploaded to a per-frame buffer, so text dragged by a grip
+    /// stays visible even though it's hidden from the base text set (issue #316).
+    pub(in crate::scene) preview_text_verts:
+        Arc<Vec<crate::scene::pipeline::text_gpu::TextVertex>>,
     /// Per-entity normalized draw-order depth (handle.value() → (0,1)), used
     /// by the wire / face3d pipelines as a clip-z bias. WireModels carry no
     /// depth field (84 construction sites); the bias is looked up by handle
@@ -380,6 +385,7 @@ impl shader::Primitive for Primitive {
             // refreshed every frame it's present, so a drag never re-uploads
             // the resident base wire buffer.
             inner.upload_preview_wires(device, &vp.preview_wires[..], &vp.draw_depths);
+            inner.upload_preview_text(device, queue, &vp.preview_text_verts[..]);
             // Cull / scissor / LOD project AABBs relative-to-eye (matching the
             // GPU's RTE path) so the math stays precise at UTM-scale coords.
             let view_rot = vp.uniforms.view_rot;
@@ -524,6 +530,20 @@ fn render_signature(vp: &ViewportData, clip_w: u32, clip_h: u32) -> u64 {
             p[2].to_bits().hash(&mut h);
         }
     }
+    // Grip-drag / command-preview glyph quads (issue #316). A pure-text slide
+    // leaves `preview_wires` empty and moves ONLY these, so a signature that
+    // ignored them would let the scene-render cache freeze the dragged text at
+    // its first frame (re-blitting a stale texture) until release. Small — one
+    // dragged entity — so hashing every vertex is cheap. Hash the high AND low
+    // halves of the double-single position: a sub-unit slide at UTM scale shifts
+    // only the low residual, so hashing the high f32 alone would miss it.
+    vp.preview_text_verts.len().hash(&mut h);
+    for v in vp.preview_text_verts.iter() {
+        v.pos[0].to_bits().hash(&mut h);
+        v.pos[1].to_bits().hash(&mut h);
+        v.pos_low[0].to_bits().hash(&mut h);
+        v.pos_low[1].to_bits().hash(&mut h);
+    }
     h.finish()
 }
 
@@ -1106,11 +1126,21 @@ impl Scene {
         // draws only the text that belongs to it. Cached on the wire content
         // id so an unchanged wire set is not re-walked every frame.
         let text_verts = self.gather_text_verts(&all_wires, wire_content_id);
+        // Grip-drag / command-preview glyphs live on `self.preview_text` (set by
+        // the edit handlers), excluded from the epoch-cached base gather above.
+        // Clone the (tiny — one dragged entity) set per frame so dragged text
+        // stays on screen without re-uploading the resident base buffer (#316).
+        let preview_text_verts = if self.preview_text.is_empty() {
+            Arc::new(Vec::new())
+        } else {
+            Arc::new(self.preview_text.clone())
+        };
         Some(ViewportData {
             wires: all_wires,
             preview_wires,
             face3d_wires,
             text_verts,
+            preview_text_verts,
             draw_depths: self.draw_depth_map(),
             hatches,
             wipeout_hatches,