Fix H2C start G-code record-data comments (#16406)

This fixes the H2C start G-code template by commenting the two
`========== record data ==========` separator lines.

Those lines are currently emitted as raw text inside
`machine_start_gcode`. Since they are not comments or G-code commands,
they can make the generated start sequence invalid or firmware-dependent
when the template is used. The fix preserves the separators as comments.

Fixes #16218.

Validation:
- Parsed the modified JSON profile with Python `json.loads`.
- Checked both `record data` separator lines now start with `;` after
unescaping the G-code string.

.github/workflows/clang_tidy.yml

@@ -16,6 +16,15 @@ on:
 
 permissions:
   contents: read
+  # Listing caches and builds while waiting for a deps cache.
+  actions: read
+
+# Read by scripts/ci_deps_cache.sh.
+env:
+  REPO: ${{ github.repository }}
+  WORKFLOW: build_all.yml
+  BASE_REF: ${{ github.base_ref }}
+  JOB: build_linux (${{ vars.SELF_HOSTED && 'orca-lnx-server' || 'ubuntu-24.04' }})
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
@@ -35,7 +44,7 @@ jobs:
           # The PR merge commit plus its first parent, the base it is diffed against.
           fetch-depth: 2
 
-      - name: Look for changed C++ files
+      - name: Look for changed files
         id: changes
         run: |
           if git -c core.quotePath=false diff --name-only HEAD^1 -- src tests | grep -qE '\.(cpp|cc|cxx|hpp|h|hxx)$'; then
@@ -43,18 +52,75 @@ jobs:
           else
             echo "No C++ changes under src/ or tests/."
           fi
+          if ! git diff --quiet HEAD^1 -- deps; then
+            echo "deps=true" >> "$GITHUB_OUTPUT"
+          fi
+          echo "deps-key=linux-clang-cache-orcaslicer_deps-build-${{ hashFiles('deps/**') }}" >> "$GITHUB_OUTPUT"
 
-      # Parsing needs the dependency headers, not a build of this PR's deps/, so
-      # a PR that changes deps/ falls back to the newest cache main has.
+      # Parsing needs the dependency headers, not a build of this PR's deps/.
+      # Without an exact match the job waits for the build that saves it: this
+      # PR's own when it changes deps/, otherwise a running push build of the
+      # base branch with the same deps. With neither, a PR that keeps deps/
+      # falls back to the newest cache.
       - name: Restore cached deps
+        id: deps_cache
         if: steps.changes.outputs.cpp == 'true'
         uses: actions/cache/restore@v6
         with:
           path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
-          key: linux-clang-cache-orcaslicer_deps-build-${{ hashFiles('deps/**') }}
+          key: ${{ steps.changes.outputs.deps-key }}
+
+      - name: Look for a build to wait for
+        id: wait_check
+        if: steps.changes.outputs.cpp == 'true' && steps.deps_cache.outputs.cache-hit != 'true'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: bash scripts/ci_deps_cache.sh ${{ steps.changes.outputs.deps == 'true' && 'own' || 'check' }}
+
+      # Linux Build Deps takes about 35 minutes on GitHub-hosted runners. The
+      # wait ends early when the deps job fails.
+      - name: Wait for the deps cache
+        if: steps.wait_check.outputs.wait-for != ''
+        timeout-minutes: 100
+        env:
+          GH_TOKEN: ${{ github.token }}
+          KEY: ${{ steps.changes.outputs.deps-key }}
+          CACHE_REF: ${{ steps.changes.outputs.deps == 'true' && github.ref || format('refs/heads/{0}', github.base_ref) }}
+          KEY_INPUTS: ${{ steps.wait_check.outputs.key-inputs }}
+          WAIT_FOR: ${{ steps.wait_check.outputs.wait-for }}
+          WAIT_SINCE: ${{ steps.wait_check.outputs.wait-since }}
+          WAIT_MINUTES: 90
+        run: bash scripts/ci_deps_cache.sh wait
+
+      - name: Restore the deps cache after waiting
+        id: waited_cache
+        if: steps.wait_check.outputs.wait-for != ''
+        uses: actions/cache/restore@v6
+        with:
+          path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
+          key: ${{ steps.changes.outputs.deps-key }}
+
+      - name: Fail without this PR's deps cache
+        if: steps.changes.outputs.deps == 'true' && steps.wait_check.outcome == 'success' && steps.waited_cache.outputs.cache-hit != 'true'
+        run: |
+          echo "::error::No deps cache ${{ steps.changes.outputs.deps-key }}. Check this PR's Linux Build Deps job, then rerun clang-tidy."
+          exit 1
+
+      - name: Restore the newest cached deps
+        id: newest_cache
+        if: steps.changes.outputs.deps != 'true' && steps.wait_check.outcome == 'success' && steps.waited_cache.outputs.cache-hit != 'true'
+        uses: actions/cache/restore@v6
+        with:
+          path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
+          key: ${{ steps.changes.outputs.deps-key }}
           restore-keys: linux-clang-cache-orcaslicer_deps-build-
           fail-on-cache-miss: true
 
+      - name: Warn about older deps
+        if: steps.newest_cache.outcome == 'success' && steps.newest_cache.outputs.cache-hit != 'true'
+        run: echo "::warning title=Older deps::No cache matches this PR's deps/, so clang-tidy parsed against ${{ steps.newest_cache.outputs.cache-matched-key }}. If it reports errors in code that uses a dependency, rerun clang-tidy once the base branch's Build all has saved the new deps."
+
       - name: Apt-Install Dependencies
         if: steps.changes.outputs.cpp == 'true' && !vars.SELF_HOSTED
         uses: ./.github/actions/apt-install-deps

resources/profiles/BBL.json

@@ -1,7 +1,7 @@
 {
 	"name": "Bambulab",
 	"url": "http://www.bambulab.com/Parameters/vendor/BBL.json",
-	"version": "02.08.00.14",
+	"version": "02.08.00.15",
 	"force_update": "0",
 	"description": "the initial version of BBL configurations",
 	"machine_model_list": [

scripts/ci_deps_cache.sh

@@ -1,21 +1,27 @@
 #!/usr/bin/env bash
-# Lets a pull request's macOS deps build wait for a push build of the base
-# branch that builds the same deps, from a Linux job. `check` runs after a cache
-# miss and names a queued or running base build with the same deps/ and .github/
-# to wait for, unless the pull request changes either. `wait` waits until that
-# build saves KEY. actions/cache then confirms the entry can be restored.
+# Lets a pull request's macOS deps build, or its clang-tidy job, wait for a
+# build that saves the deps cache it needs, from a Linux job. `check` runs after
+# a cache miss and names a queued or running push build of the base branch with
+# the same deps/ and .github/ to wait for, unless the pull request changes either.
+# `own` names the pull request's own build instead, for clang-tidy when the pull
+# request changes deps/. `wait` waits until that build saves KEY under CACHE_REF,
+# or its deps job fails. actions/cache then confirms the entry can be restored.
 #
-# Environment: GH_TOKEN, REPO, WORKFLOW_REF and BASE_REF, plus KEY_INPUTS,
-# WAIT_FOR, WAIT_SINCE, WAIT_MINUTES, KEY and ARCH for `wait`.
+# Environment: GH_TOKEN, REPO, WORKFLOW_REF (or WORKFLOW, the build workflow's
+# file name) and BASE_REF, plus HEAD_SHA for `own`, and KEY_INPUTS, WAIT_FOR,
+# WAIT_SINCE, WAIT_MINUTES, KEY, CACHE_REF (default the base branch) and ARCH
+# (or JOB, the matrix job's name) for `wait`.
 # Writes key-inputs, wait-for and wait-since to $GITHUB_OUTPUT.
 set -uo pipefail
 
-workflow=${WORKFLOW_REF%%@*}
-workflow=${workflow##*/}
+workflow=${WORKFLOW_REF:-}
+workflow=${workflow%%@*}
+workflow=${WORKFLOW:-${workflow##*/}}
 
 # Must match the job names in build_all.yml, build_check_cache.yml and build_deps.yml.
-check_job_name="build_macos_arch (${ARCH:-}) / Check Cache"
-deps_job_name="build_macos_arch (${ARCH:-}) / Build Deps / Build Deps"
+job=${JOB:-build_macos_arch (${ARCH:-})}
+check_job_name="$job / Check Cache"
+deps_job_name="$job / Build Deps / Build Deps"
 
 out() { echo "$1" >> "${GITHUB_OUTPUT:-/dev/stdout}"; }
 
@@ -63,8 +69,27 @@ check() {
   fi
 }
 
+own() {
+  out "key-inputs=$(local_key_inputs HEAD)"
+  local id
+  # The build can be created a moment after this job.
+  for _ in 1 2 3 4 5; do
+    id=$(gh api -X GET "repos/$REPO/actions/workflows/$workflow/runs" \
+      -f head_sha="$HEAD_SHA" -f event=pull_request -f per_page=1 --jq '.workflow_runs[0].id // empty' < /dev/null)
+    [ -n "$id" ] && break
+    sleep 30
+  done
+  if [ -n "$id" ]; then
+    echo "Waiting for the deps cache of build $id of this pull request."
+    out "wait-for=$id"
+    out "wait-since=$(date +%s)"
+  else
+    echo "No build of this pull request is building its deps."
+  fi
+}
+
 key_saved() {
-  gh cache list -R "$REPO" --ref "refs/heads/$BASE_REF" --key "$KEY" --json key < /dev/null \
+  gh cache list -R "$REPO" --ref "${CACHE_REF:-refs/heads/$BASE_REF}" --key "$KEY" --json key < /dev/null \
     | jq -e --arg key "$KEY" 'any(.[]; .key == $key)' > /dev/null
 }
 
@@ -87,11 +112,11 @@ wait_for() {
           key_saved && { echo "Found $KEY."; return; }
           sleep 20
         done
-        echo "Build $id of $BASE_REF finished its deps without saving $KEY."
+        echo "Build $id finished its deps without saving $KEY."
         return ;;
       "completed cancelled") ;;
       completed*)
-        echo "The deps job of build $id of $BASE_REF did not succeed."
+        echo "The deps job of build $id did not succeed."
         return ;;
       # The deps job exists only once the build's cache check has succeeded.
       "")
@@ -100,7 +125,7 @@ wait_for() {
           completed*)
             check=$(jq -r --arg name "$check_job_name" 'first(.jobs[] | select(.name == $name) | .conclusion) // ""' <<< "$jobs")
             if [ -z "$warned" ] && { [ -z "$check" ] || [ "$check" = success ]; }; then
-              echo "::warning title=Deps wait::Build $id of $BASE_REF has no job named \"$deps_job_name\". If the build jobs were renamed, update scripts/ci_deps_cache.sh. This does not affect this pull request."
+              echo "::warning title=Deps wait::Build $id has no job named \"$deps_job_name\". If the build jobs were renamed, update scripts/ci_deps_cache.sh. This does not affect this pull request."
               warned=1
             fi ;;
           *)
@@ -118,11 +143,12 @@ wait_for() {
     seen="$seen $id"
     echo "Following build $id of $BASE_REF."
   done
-  echo "No build of $BASE_REF saved $KEY."
+  echo "No build saved $KEY."
 }
 
 case "${1:-}" in
   check) check ;;
+  own) own ;;
   wait) wait_for ;;
-  *) echo "usage: $0 check|wait" >&2; exit 2 ;;
+  *) echo "usage: $0 check|own|wait" >&2; exit 2 ;;
 esac

src/libslic3r/Print.cpp

@@ -2991,6 +2991,15 @@ void  PrintObject::clear_shared_object()
 void  PrintObject::copy_layers_from_shared_object()
 {
     if (m_shared_object) {
+        // Orca: Print::process() calls this once per slice for each sharing object, after clear_shared_object() has
+        // emptied any earlier alias, so the vectors hold only layers this object sliced itself before it started sharing
+        // (or nothing). Free them here, as clear_support_layers() / clear_layers() would; those skip deletion while
+        // m_shared_object is set. The belt-only data they also free is always empty here, because belt printers never
+        // share layers.
+        for (SupportLayer *layer : m_support_layers)
+            delete layer;
+        for (Layer *layer : m_layers)
+            delete layer;
         m_layers.clear();
         m_support_layers.clear();
 

src/libslic3r/PrintObject.cpp

@@ -982,6 +982,9 @@ void PrintObject::generate_support_material(bool with_belt_brim)
             this->_generate_support_material();
             m_print->throw_if_canceled();
         }
+        // Orca: the tree support collision/avoidance caches and support nodes are only used while this step runs
+        // (detect_overhangs() rebuilds them from scratch), so don't keep them resident until the next slice.
+        this->clear_tree_support_preview_cache();
         // Belt brim rides here rather than in the brim step because its apron
         // prologue introduces print_z values below the object's first layer, and
         // those must exist before ToolOrdering is built at psWipeTower - one step

src/libslic3r/PrintObjectSlice.cpp

@@ -1532,7 +1532,7 @@ void PrintObject::slice_volumes()
                         if (min_growth < 0.f || elfoot > 0.f) {
                             // Apply the negative XY compensation. (the ones that is <0)
                             ExPolygons trimming;
-                            static const float eps = float(scale_(m_config.slice_closing_radius.value) * 1.5);
+                            const float eps = float(scale_(m_config.slice_closing_radius.value) * 1.5);
                             if (elfoot > 0.f) {
                                 ExPolygons expolygons_to_compensate = offset_ex(layer->merged(eps), -eps);
                                 lslices_elfoot_uncompensated[layer_id] = expolygons_to_compensate;

src/libslic3r/Support/TreeSupport.cpp

@@ -1976,37 +1976,15 @@ coordf_t TreeSupport::get_radius(const SupportNode* node)
     return node->radius;
 }
 
-ExPolygons TreeSupport::get_avoidance(coordf_t radius, size_t obj_layer_nr)
+// Orca: drop_nodes() calls these several times per node per layer, so they return a reference into the
+// TreeSupportData cache. The cache only ever inserts, so its entries never move while nodes drop in parallel.
+const ExPolygons& TreeSupport::get_avoidance(coordf_t radius, size_t obj_layer_nr)
 {
-#if USE_SUPPORT_3D
-    if (m_model_volumes) {
-        bool on_build_plate = m_object_config->support_on_build_plate_only.value;
-        const Polygons& avoid_polys = m_model_volumes->getAvoidance(radius, obj_layer_nr, TreeSupport3D::TreeModelVolumes::AvoidanceType::FastSafe, on_build_plate, true);
-        ExPolygons expolys;
-        for (auto& poly : avoid_polys)
-            expolys.emplace_back(std::move(poly));
-        return expolys;
-    }
-    return ExPolygons();
-#else
     return m_ts_data->get_avoidance(radius, obj_layer_nr);
-#endif
 }
-ExPolygons TreeSupport::get_collision(coordf_t radius, size_t layer_nr)
+const ExPolygons& TreeSupport::get_collision(coordf_t radius, size_t layer_nr)
 {
-#if USE_SUPPORT_3D
-    if (m_model_volumes) {
-        bool on_build_plate = m_object_config->support_on_build_plate_only.value;
-        const Polygons& collision_polys = m_model_volumes->getCollision(radius, layer_nr, true);
-        ExPolygons expolys;
-        for (auto& poly : collision_polys)
-            expolys.emplace_back(std::move(poly));
-        return expolys;
-    }
-#else
     return m_ts_data->get_collision(radius, layer_nr);
-#endif
-    return ExPolygons();
 }
 Polygons TreeSupport::get_collision_polys(coordf_t radius, size_t layer_nr)
 {
@@ -2827,7 +2805,12 @@ void TreeSupport::draw_circles()
 #endif  // SUPPORT_TREE_DEBUG_TO_SVG
 
     SupportLayerPtrs& ts_layers = m_object->support_layers();
-    auto iter = std::remove_if(ts_layers.begin(), ts_layers.end(), [](SupportLayer* ts_layer) { return ts_layer->height < EPSILON; });
+    // Orca: the vector owns its layers, so the dropped ones are deleted before they are erased.
+    // std::stable_partition (unlike std::remove_if) leaves exactly the dropped layers in the tail.
+    // Only heights below EPSILON are dropped; written as !(height < EPSILON), a NaN height is kept.
+    auto iter = std::stable_partition(ts_layers.begin(), ts_layers.end(), [](SupportLayer* ts_layer) { return !(ts_layer->height < EPSILON); });
+    for (auto it = iter; it != ts_layers.end(); ++it)
+        delete *it;
     ts_layers.erase(iter, ts_layers.end());
     for (int layer_nr = 0; layer_nr < ts_layers.size(); layer_nr++) {
         ts_layers[layer_nr]->upper_layer = layer_nr != ts_layers.size() - 1 ? ts_layers[layer_nr + 1] : nullptr;
@@ -3071,7 +3054,7 @@ void TreeSupport::drop_nodes()
                     //Insert a completely new node and let both original nodes fade.
                     Point next_position = (node.position + neighbours[0]) / 2; //Average position of the two nodes.
                     coordf_t next_radius = calc_radius(node.dist_mm_to_top+height_next);
-                    auto avoid_layer = get_avoidance(next_radius, obj_layer_nr_next);
+                    const ExPolygons& avoid_layer = get_avoidance(next_radius, obj_layer_nr_next);
                     if (group_index == 0)
                     {
                         //Avoid collisions.
@@ -3275,7 +3258,7 @@ void TreeSupport::drop_nodes()
                 }
 #endif
                 coordf_t next_radius = calc_radius(node.dist_mm_to_top + height_next);
-                auto avoidance_next = get_avoidance(next_radius, obj_layer_nr_next);
+                const ExPolygons& avoidance_next = get_avoidance(next_radius, obj_layer_nr_next);
 
                 Point  to_outside         = projection_onto(avoidance_next, node.position);
                 Point  direction_to_outer = to_outside - node.position;
@@ -3337,7 +3320,7 @@ void TreeSupport::drop_nodes()
                     p_node->to_buildplate = false;
                     return; // from parallel_for_each lambda
                 }
-                auto              next_collision = get_collision(0, obj_layer_nr_next);
+                const ExPolygons& next_collision = get_collision(0, obj_layer_nr_next);
                 const bool   to_buildplate  = !is_inside_ex(m_ts_data->m_layer_outlines[obj_layer_nr_next], next_layer_vertex);
                 // don't increase radius if next node will collide partially with the object (STUDIO-7883)
                 to_outside             = projection_onto(next_collision, next_layer_vertex);

src/libslic3r/Support/TreeSupport.hpp

@@ -536,9 +536,9 @@ private:
     coordf_t calc_branch_radius(coordf_t base_radius, coordf_t mm_to_top, double diameter_angle_scale_factor, bool use_min_distance=true);
     coordf_t   calc_radius(coordf_t mm_to_top);
     coordf_t get_radius(const SupportNode* node);
-    ExPolygons get_avoidance(coordf_t radius, size_t obj_layer_nr);
+    const ExPolygons& get_avoidance(coordf_t radius, size_t obj_layer_nr);
     // layer's expolygon expanded by radius+m_xy_distance
-    ExPolygons get_collision(coordf_t radius, size_t layer_nr);
+    const ExPolygons& get_collision(coordf_t radius, size_t layer_nr);
     // get Polygons instead of ExPolygons
     Polygons get_collision_polys(coordf_t radius, size_t layer_nr);
 

src/libvgcode/src/SegmentTemplate.cpp

@@ -21,7 +21,9 @@ namespace libvgcode {
 // the triangles that share it: the shader runs 8 times per segment instead of 24.
 static constexpr const std::array<uint8_t, 8> VERTEX_DATA = { 0, 1, 2, 3, 4, 5, 6, 7 };
 
-static constexpr const std::array<uint8_t, 24> INDEX_DATA = {
+// 16-bit indices: GCN 1/2 GPUs have no 8-bit index support, and some of their drivers
+// emulate it wrongly in instanced draws.
+static constexpr const std::array<uint16_t, 24> INDEX_DATA = {
     0, 1, 2, // front spike
     0, 2, 3, // front spike
     0, 3, 4, // right/bottom body 
@@ -37,7 +39,7 @@ void SegmentTemplate::init()
     if (m_vao_id != 0)
         return;
 
-    m_size_in_bytes_gpu += (VERTEX_DATA.size() + INDEX_DATA.size()) * sizeof(uint8_t);
+    m_size_in_bytes_gpu += VERTEX_DATA.size() * sizeof(uint8_t) + INDEX_DATA.size() * sizeof(uint16_t);
 
     int curr_vertex_array;
     glsafe(glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &curr_vertex_array));
@@ -61,7 +63,7 @@ void SegmentTemplate::init()
     // and restored together with the vao.
     glsafe(glGenBuffers(1, &m_ibo_id));
     glsafe(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_ibo_id));
-    glsafe(glBufferData(GL_ELEMENT_ARRAY_BUFFER, INDEX_DATA.size() * sizeof(uint8_t), INDEX_DATA.data(), GL_STATIC_DRAW));
+    glsafe(glBufferData(GL_ELEMENT_ARRAY_BUFFER, INDEX_DATA.size() * sizeof(uint16_t), INDEX_DATA.data(), GL_STATIC_DRAW));
 
     glsafe(glBindBuffer(GL_ARRAY_BUFFER, curr_array_buffer));
     glsafe(glBindVertexArray(curr_vertex_array));
@@ -94,7 +96,7 @@ void SegmentTemplate::render(size_t count)
     glsafe(glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &curr_vertex_array));
 
     glsafe(glBindVertexArray(m_vao_id));
-    glsafe(glDrawElementsInstanced(GL_TRIANGLES, static_cast<GLsizei>(INDEX_DATA.size()), GL_UNSIGNED_BYTE,
+    glsafe(glDrawElementsInstanced(GL_TRIANGLES, static_cast<GLsizei>(INDEX_DATA.size()), GL_UNSIGNED_SHORT,
                                    nullptr, static_cast<GLsizei>(count)));
     glsafe(glBindVertexArray(curr_vertex_array));
 }

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.cpp

@@ -1036,6 +1036,11 @@ bool GLGizmoPainterBase::on_mouse(const wxMouseEvent &mouse_event)
     Vec2d mouse_pos = mouse_coord.cast<double>();
 
     if (mouse_event.Moving()) {
+        // No button is down, yet a stroke is still open: its release went elsewhere, as a paint drag does not
+        // capture the mouse. End the stroke as that release would have.
+        if (m_button_down != Button::None)
+            gizmo_event(m_button_down == Button::Left ? SLAGizmoEventType::LeftUp : SLAGizmoEventType::RightUp, mouse_pos,
+                        mouse_event.ShiftDown(), mouse_event.AltDown(), false);
         gizmo_event(SLAGizmoEventType::Moving, mouse_pos, mouse_event.ShiftDown(), mouse_event.AltDown(), false);
         return false;
     }
@@ -1205,6 +1210,10 @@ void GLGizmoPainterBase::on_set_state()
         m_old_mo_id = -1;
         //m_iva.release_geometry();
         m_triangle_selectors.clear();
+        // A stroke still open goes with the selectors. Its state must not carry into the next session, where the
+        // first move would end it as if released and the first press would paint a line from its last position.
+        m_button_down      = Button::None;
+        m_last_mouse_click = Vec2d::Zero();
 
         //Camera& camera = wxGetApp().plater()->get_camera();
         //camera.look_at(camera.get_position(), m_previous_target, Vec3d::UnitZ());

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -562,6 +562,11 @@ void GLGizmoTextureDisplacement::on_shutdown()
     m_shaded_island_delta  = Eigen::Matrix<float, 2, 3>::Identity();
     m_island_drag_active = false;
     m_island_move_set.clear();
+    // The pane closes below, taking the highlight with it, and the view must not open the next session in a
+    // Fast the user never picked. Set directly: nothing is to be queued against a gizmo that is closing.
+    if (m_island_view.switched)
+        m_use_shaded_preview = false;
+    m_island_view = IslandViewFollow{};
     m_adjust_texture_mode = false;
     m_seam_edit_mode      = false;
     m_adjust_drag_handle  = AdjustHandle::None;
@@ -727,18 +732,13 @@ void GLGizmoTextureDisplacement::render_painter_gizmo()
 
     // The UV editor's island selection, shown on the model. Polled here rather than pushed: the pane
     // changes its selection in its own mouse handling, and a compare of a few ints per frame is free.
-    {
-        const TextureDisplacementLayer *al = active_layer();
-        const UVEditorCanvas           *uv_canvas = wxGetApp().plater()->get_uv_editor_canvas();
-        if (m_show_uv_editor && al != nullptr && al->projection_method == TextureProjectionMethod::LSCM &&
-            uv_canvas != nullptr && !m_uv_editor_unwrap.empty()) {
-            if (uv_canvas->selected_islands() != m_island_overlay_selection)
-                rebuild_island_overlay(uv_canvas->selected_islands());
-            render_island_overlay();
-        } else if (m_island_overlay_glmodel.is_initialized()) {
-            m_island_overlay_glmodel.reset();
-            m_island_overlay_selection.clear();
-        }
+    if (const std::vector<int> *islands = island_highlight_selection()) {
+        if (*islands != m_island_overlay_selection)
+            rebuild_island_overlay(*islands);
+        render_island_overlay();
+    } else if (m_island_overlay_glmodel.is_initialized()) {
+        m_island_overlay_glmodel.reset();
+        m_island_overlay_selection.clear();
     }
 
     // Diagnostic overlays, drawn on top of whatever preview is active (both pull toward the camera
@@ -1520,7 +1520,7 @@ void GLGizmoTextureDisplacement::render_shaded_preview_mesh()
     // is box-filtered down to 128 px for a ~48 px row, and feeding it to the shader cost the preview
     // three quarters of the height map's detail - and, since height_tex_texel is derived from it, also
     // flattened the shading gradient and made the parallax march skip itself at angles where it should
-    // run. Cached on the image_data pointer + smoothing, so no PNG is decoded per frame.
+    // run. Cached per image_data and smoothing, so no PNG is decoded per frame.
     GLTexture *tex = get_layer_height_texture(*layer);
     if (tex == nullptr || tex->get_width() <= 0 || tex->get_height() <= 0)
         return;
@@ -1926,6 +1926,16 @@ void GLGizmoTextureDisplacement::render_paint_overlay(GLModel &overlay)
     shader->stop_using();
 }
 
+const std::vector<int> *GLGizmoTextureDisplacement::island_highlight_selection()
+{
+    const TextureDisplacementLayer *al        = active_layer();
+    const UVEditorCanvas           *uv_canvas = wxGetApp().plater()->get_uv_editor_canvas();
+    if (m_show_uv_editor && al != nullptr && al->projection_method == TextureProjectionMethod::LSCM &&
+        uv_canvas != nullptr && !m_uv_editor_unwrap.empty())
+        return &uv_canvas->selected_islands();
+    return nullptr;
+}
+
 void GLGizmoTextureDisplacement::rebuild_island_overlay(const std::vector<int> &selection)
 {
     m_island_overlay_glmodel.reset();
@@ -2651,6 +2661,37 @@ void GLGizmoTextureDisplacement::apply_view_mode(int mode)
     m_parent.set_as_dirty();
 }
 
+int GLGizmoTextureDisplacement::view_mode() const
+{
+    return m_use_shaded_preview                         ? 1 :
+           m_uv_check_mode == UVCheckMode::Checker    ? 2 :
+           m_uv_check_mode == UVCheckMode::Distortion ? 3 : 0;
+}
+
+int GLGizmoTextureDisplacement::IslandViewFollow::step(bool shown_now, int view, bool debug_open)
+{
+    shown = shown_now;
+    if (!shown) {
+        // The view is back to Normal already if a debug stage took it, and Normal applied over a stage would
+        // queue a preview job that replaces the stage being inspected.
+        const bool restore = switched && view == 1;
+        switched = keep_normal = false;
+        return restore ? 0 : -1;
+    }
+    if (view != 0 || keep_normal || debug_open)
+        return -1;
+    switched = true;
+    return 1;
+}
+
+void GLGizmoTextureDisplacement::follow_island_highlight()
+{
+    const std::vector<int> *islands = island_highlight_selection();
+    const int view = m_island_view.step(islands != nullptr && !islands->empty(), view_mode(), m_debug_stage >= 0);
+    if (view >= 0)
+        apply_view_mode(view);
+}
+
 void GLGizmoTextureDisplacement::push_uv_pane_state()
 {
     UVEditorCanvas *canvas = wxGetApp().plater()->get_uv_editor_canvas();
@@ -2891,7 +2932,8 @@ void GLGizmoTextureDisplacement::run_uv_command(int cmd, float value)
             rebuild_preview();
         }
     }
-    // FrameAll/ToggleSnap are handled inside the canvas; ProjectFromView is not wired yet.
+    // FrameAll/ToggleSnap are handled inside the canvas; ProjectFromView is not wired yet. SelectionChanged
+    // only asks for this frame: follow_island_highlight() and the overlay read the selection back themselves.
     m_parent.set_as_dirty();
 }
 
@@ -4038,8 +4080,8 @@ void GLGizmoTextureDisplacement::remove_texture_layer(int slot)
     if (slot >= 0 && slot < int(TEXTURE_DISPLACEMENT_MAX_LAYERS)) {
         mv->texture_displacement_facet(slot).reset();
         m_thumbnails[size_t(slot)].reset();
-        m_thumbnail_source[size_t(slot)] = nullptr;
-        m_layer_expanded[size_t(slot)]   = false;
+        m_thumbnail_source[size_t(slot)].reset();
+        m_layer_expanded[size_t(slot)] = false;
     }
     if (m_picker_slot == slot)
         m_picker_slot = -1;
@@ -4213,7 +4255,7 @@ int GLGizmoTextureDisplacement::select_visible_faces(const std::array<float, 12>
     selector.reset();
     for (unsigned i : unobscured)
         selector.set_facet(int(front_facing[i]), EnforcerBlockerType::ENFORCER);
-    selector.request_update_render_data();
+    selector.request_update_render_data(true);
 
     update_model_object();
     m_parent.set_as_dirty();
@@ -4236,7 +4278,7 @@ void GLGizmoTextureDisplacement::select_whole_model()
         const size_t facet_count = v->mesh().its.indices.size();
         for (size_t i = 0; i < facet_count; ++i)
             m_triangle_selectors[idx]->set_facet(int(i), EnforcerBlockerType::ENFORCER);
-        m_triangle_selectors[idx]->request_update_render_data();
+        m_triangle_selectors[idx]->request_update_render_data(true);
     }
     update_model_object();
     m_parent.set_as_dirty();
@@ -5342,7 +5384,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
         return nullptr;
 
     const size_t slot = size_t(layer.slot);
-    if (m_thumbnails[slot] && m_thumbnail_source[slot] == layer.image_data.get() &&
+    if (m_thumbnails[slot] && m_thumbnail_source[slot].lock() == layer.image_data &&
         m_thumbnail_smoothing[slot] == layer.smoothing)
         return m_thumbnails[slot].get();
 
@@ -5355,7 +5397,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
         return nullptr;
 
     m_thumbnails[slot]          = std::move(texture);
-    m_thumbnail_source[slot]    = layer.image_data.get();
+    m_thumbnail_source[slot]    = layer.image_data;
     m_thumbnail_smoothing[slot] = layer.smoothing;
     return m_thumbnails[slot].get();
 }
@@ -5364,17 +5406,17 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_color_texture(const TextureDisp
 {
     if (layer.empty() || !layer.color_enabled)
         return nullptr;
-    if (m_color_tex && m_color_tex_source == layer.image_data.get() && m_color_tex_smoothing == layer.smoothing)
+    if (m_color_tex && m_color_tex_source.lock() == layer.image_data && m_color_tex_smoothing == layer.smoothing)
         return m_color_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_color_texture(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
     if (!texture) {
         m_color_tex.reset();
-        m_color_tex_source = nullptr;
+        m_color_tex_source.reset();
         return nullptr;
     }
     m_color_tex           = std::move(texture);
-    m_color_tex_source    = layer.image_data.get();
+    m_color_tex_source    = layer.image_data;
     m_color_tex_smoothing = layer.smoothing;
     return m_color_tex.get();
 }
@@ -5386,7 +5428,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
 
     // One slot, not one per layer: the preview shader only ever shades the *active* layer, so a single
     // full-resolution upload is enough and the VRAM cost stays at one texture rather than eight.
-    if (m_height_tex && m_height_tex_source == layer.image_data.get() && m_height_tex_smoothing == layer.smoothing)
+    if (m_height_tex && m_height_tex_source.lock() == layer.image_data && m_height_tex_smoothing == layer.smoothing)
         return m_height_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_height_thumbnail(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
@@ -5394,7 +5436,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
         return nullptr;
 
     m_height_tex           = std::move(texture);
-    m_height_tex_source    = layer.image_data.get();
+    m_height_tex_source    = layer.image_data;
     m_height_tex_smoothing = layer.smoothing;
     return m_height_tex.get();
 }
@@ -5835,6 +5877,9 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
     GizmoImguiBegin(get_name(), flags);
     ensure_panel_icons();
     process_uv_commands(); // clicks from the UV editor pane, run here where the GL context is current
+    // After the pane's commands, which can close it or change the view, and before the View row, so the row
+    // lights the view this frame ends up in and a click on it has the last word.
+    follow_island_highlight();
     const float previous_body_h   = m_panel_body_h;
     const float previous_footer_h = m_panel_footer_h;
 
@@ -6281,7 +6326,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                 if (v->is_model_part()) {
                     ++idx;
                     m_triangle_selectors[idx]->reset();
-                    m_triangle_selectors[idx]->request_update_render_data();
+                    m_triangle_selectors[idx]->request_update_render_data(true);
                 }
             update_model_object();
             m_parent.set_as_dirty();
@@ -6323,10 +6368,9 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
     // ---- View: Normal / Fast / Checker / Distortion as one group, Wireframe on its own ----
     // The underlying state stays m_use_shaded_preview + m_uv_check_mode.
     {
-        const int cur_mode = m_use_shaded_preview                               ? 1 :
-                             m_uv_check_mode == UVCheckMode::Checker    ? 2 :
-                             m_uv_check_mode == UVCheckMode::Distortion ? 3 : 0;
+        const int cur_mode = view_mode();
         int  new_mode       = cur_mode;
+        int  picked         = -1; // the button clicked, the active one included
         bool wf_toggle      = false;
         bool open_uv_editor = false;
         // Checker and Distortion both draw *the unwrap* - the first the texture grid laid over it, the second
@@ -6349,19 +6393,19 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         ImGui::SetCursorPosX(std::max(ImGui::GetCursorPosX(), x0 + m_imgui->scaled(2.6f)));
         if (icon_toggle(701, "texture_displacement_real_preview.svg", cur_mode == 0, icon_md, _L("Normal"),
                         _L("Normal - the real geometry, exactly what Bake will produce. Slower to update")))
-            new_mode = 0;
+            new_mode = picked = 0;
         ImGui::SameLine(0.f, gap_s);
         if (icon_toggle(702, "texture_displacement_fast_preview.svg", cur_mode == 1, icon_md, _L("Fast"),
                         _L("Fast - the relief is only shaded on, not built, and only for the layer you are "
                            "editing. Updates instantly while you paint")))
-            new_mode = 1;
+            new_mode = picked = 1;
         ImGui::SameLine(0.f, gap_s);
         if (icon_toggle(703, "texture_displacement_checker.svg", cur_mode == 2, icon_md, _L("Checker"),
                         _L("Checker - a test grid instead of the texture. Where the squares stay square the "
                            "texture is undistorted; where they stretch, it will too. Opens the UV editor if "
                            "it is closed"),
                         uv_view_na)) {
-            new_mode       = 2;
+            new_mode       = picked = 2;
             open_uv_editor = true;
         }
         ImGui::SameLine(0.f, gap_s);
@@ -6369,7 +6413,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                         _L("Distortion - blue-to-red stretch heatmap over the unwrap. Opens the UV editor if "
                            "it is closed"),
                         uv_view_na)) {
-            new_mode       = 3;
+            new_mode       = picked = 3;
             open_uv_editor = true;
         }
         vsep(icon_md);
@@ -6393,6 +6437,8 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
             if (new_mode == cur_mode)
                 update_uv_editor(); // otherwise apply_view_mode() below does it
         }
+        if (picked >= 0)
+            m_island_view.picked(picked);
         if (new_mode != cur_mode)
             apply_view_mode(new_mode);
         if (wf_toggle) {

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp

@@ -197,6 +197,27 @@ public:
     };
     static PaintedColors painted_colors(const TriangleMesh &mesh, const TriangleSelector::TriangleSplittingData &paint);
 
+    // The view while the UV editor's selected islands are highlighted on the model. The highlight lies on the
+    // undisplaced surface, so the Normal view's relief hides it wherever it rises: Normal gives way to Fast
+    // while islands are selected and comes back once none are. A view the user clicks in the View row is
+    // theirs - the pane's background buttons are not a pick, Height only meaning "the texture view".
+    struct IslandViewFollow
+    {
+        bool shown       = false; // the highlight, as of the last step()
+        bool switched    = false; // Fast was switched on for the highlight, so Normal comes back once it is gone
+        bool keep_normal = false; // the user picked Normal in the View row while the highlight was shown
+        // The view to apply this frame (0 Normal, 1 Fast), or -1 for none. `view` is the one on screen, numbered as
+        // apply_view_mode() takes it; `debug_open` a debug stage on screen, which holds Normal itself.
+        int  step(bool shown_now, int view, bool debug_open);
+        // A View row button clicked, the active one included. The row is drawn after step() in the same frame,
+        // so `shown` is this frame's.
+        void picked(int view)
+        {
+            switched    = false;
+            keep_normal = shown && view == 0;
+        }
+    };
+
     void render_painter_gizmo() override;
 
     // Intercepts mouse input while "Adjust Texture" mode is on (dragging the on-canvas offset/
@@ -513,6 +534,11 @@ private:
     // The panel's view modes: 0 Normal, 1 Fast, 2 Checker, 3 Distortion. Shared by the View row and the pane's
     // background buttons, so both switch views the same way.
     void apply_view_mode(int mode);
+    // The view on screen, numbered as apply_view_mode() takes it.
+    int  view_mode() const;
+    // Run once a frame, after the pane's commands: switches the view as m_island_view says.
+    void             follow_island_highlight();
+    IslandViewFollow m_island_view;
     // The pane header's thumbnail of the active layer's texture, rebuilt only when its image changes.
     static constexpr int       UV_THUMB_PX       = 64;
     const void                *m_uv_thumb_source = nullptr;
@@ -744,6 +770,8 @@ private:
     // in place. Rebuilt whenever the pane's selection differs from the one it was built for.
     GLModel          m_island_overlay_glmodel;
     std::vector<int> m_island_overlay_selection;
+    // The pane's selection while the overlay applies - the pane open over an unwrapped LSCM layer - else null.
+    const std::vector<int> *island_highlight_selection();
     void             rebuild_island_overlay(const std::vector<int> &selection);
     void             render_island_overlay();
     // Set on every paint event, cleared when the overlay is rebuilt in render_painter_gizmo(). Kept
@@ -924,25 +952,26 @@ private:
     bool m_preview_job_pending = false;
     void queue_preview_job();
 
-    // Per-slot GPU thumbnail cache for the layer list panel, keyed by the image_data pointer that
-    // was current the last time each thumbnail was built (see get_layer_thumbnail()).
-    std::array<std::unique_ptr<GLTexture>, TEXTURE_DISPLACEMENT_MAX_LAYERS> m_thumbnails;
-    std::array<const void *, TEXTURE_DISPLACEMENT_MAX_LAYERS>               m_thumbnail_source{};
+    // Per-slot GPU thumbnail cache for the layer list panel, each keyed by the image_data it was built from
+    // (see get_layer_thumbnail()). Held weakly rather than by address, as decode_height_texture()'s cache is:
+    // an image freed and replaced by another at the same address must not pass for it.
+    std::array<std::unique_ptr<GLTexture>, TEXTURE_DISPLACEMENT_MAX_LAYERS>                       m_thumbnails;
+    std::array<std::weak_ptr<const std::vector<unsigned char>>, TEXTURE_DISPLACEMENT_MAX_LAYERS> m_thumbnail_source;
     // The smoothing each cached thumbnail was built at, so a smoothing change re-uploads it.
-    std::array<float, TEXTURE_DISPLACEMENT_MAX_LAYERS>                      m_thumbnail_smoothing{};
+    std::array<float, TEXTURE_DISPLACEMENT_MAX_LAYERS>                                            m_thumbnail_smoothing{};
 
     // Full-resolution height texture for the preview shader, keyed the same way (see
     // get_layer_height_texture()). A smoothing change re-uploads it, so the fast preview shows the
     // blur the bake will apply.
-    std::unique_ptr<GLTexture> m_height_tex;
-    const void                *m_height_tex_source    = nullptr;
-    float                      m_height_tex_smoothing = -1.f;
+    std::unique_ptr<GLTexture>                      m_height_tex;
+    std::weak_ptr<const std::vector<unsigned char>> m_height_tex_source;
+    float                                           m_height_tex_smoothing = -1.f;
 
     // The same, for the layer's *colour*, which the fast preview quantizes per fragment so it shows
     // the image at texel resolution rather than at the mesh's. Null for a grayscale texture.
-    std::unique_ptr<GLTexture> m_color_tex;
-    const void                *m_color_tex_source    = nullptr;
-    float                      m_color_tex_smoothing = -1.f;
+    std::unique_ptr<GLTexture>                      m_color_tex;
+    std::weak_ptr<const std::vector<unsigned char>> m_color_tex_source;
+    float                                           m_color_tex_smoothing = -1.f;
 
     // Library textures the picker has shown at least once, keyed by file path (see LibraryTexture).
     std::map<std::string, LibraryTexture> m_library_textures;

src/slic3r/GUI/UVEditorCanvas.cpp

@@ -939,7 +939,8 @@ void UVEditorCanvas::on_mouse(wxMouseEvent &evt)
             m_active_edge = (hit.first >= 0 && is_edge_selected(hit)) ? hit : std::pair<int, int>{ -1, -1 };
             m_gesture     = (m_active_edge.first >= 0) ? Gesture::MoveEdge : Gesture::Pan;
         } else {
-            const int hit = island_at(uv);
+            const std::vector<int> selection_before = m_selection;
+            const int              hit              = island_at(uv);
             if (hit >= 0) {
                 if (evt.ShiftDown()) {
                     // Shift adds to the selection (and makes the clicked one the new primary).
@@ -969,6 +970,10 @@ void UVEditorCanvas::on_mouse(wxMouseEvent &evt)
                 m_selected_island = -1;
             }
             m_gesture = (m_selected_island >= 0) ? Gesture::MoveIsland : Gesture::Pan;
+            // The owner shows the selection on the model and would not hear of this click otherwise in time: a
+            // click that clears the selection starts no gesture, and one that sets it reports only on release.
+            if (m_selection != selection_before)
+                run_command(Command::SelectionChanged);
         }
         grab_mouse();
         Refresh();

src/slic3r/GUI/UVEditorCanvas.hpp

@@ -108,10 +108,12 @@ public:
     // the command callback - the canvas has the selection and the view, the gizmo has the layer.
     // `value` carries the new setting for the Set* commands (an angle, a flag as 0/1, or an index into
     // SelectMode / Background) and is 0 otherwise.
+    // SelectionChanged is sent by the canvas itself when a click changes the island selection. It carries
+    // nothing: the owner reads selected_islands() back, and only needs telling that it should look.
     enum class Command {
         FrameAll, ToggleSnap, AverageScale, CutSelectedIsland, ProjectFromView, JoinSelected, UnjoinSelected,
         Unwrap, SetSeamAngle, SetConnectIslands, SetSelectMode, SetMarkSeams, SetSeamPath, ClearSeams, ClearUVEdits,
-        SetBackground, PickTexture, PaneClosed
+        SetBackground, PickTexture, PaneClosed, SelectionChanged
     };
     void run_command(Command cmd, float value = 0.f);
     using CommandFn = std::function<void(Command, float)>;

tests/fff_print/test_print.cpp

@@ -43,6 +43,7 @@
 #include "libslic3r/GCode/GCodeProcessor.hpp"
 #include "libslic3r/Exception.hpp"
 #include "libslic3r/LifecycleEvents.hpp"
+#include "libslic3r/Utils.hpp"
 
 #include "test_helpers.hpp"
 #include "test_utils.hpp"
@@ -156,6 +157,81 @@ SCENARIO("Changing the number of solid shell layers does not make all surfaces i
     }
 }
 
+// Two copies of one object share a single slice. When a copy that has sliced itself becomes identical to an
+// earlier object, it keeps its own layers while that object slices and only then takes the shared layers over.
+TEST_CASE("An object that starts sharing another object's slices keeps its own layers until it takes them over", "[Print][Regression]")
+{
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.set_deserialize_strict({
+        { "layer_height",               0.2 },
+        { "initial_layer_print_height", 0.2 },
+        { "raft_layers",                1 }, // each object gets support layers of its own
+        { "sparse_infill_density",      "20%" }, // object_a's override below differs from this
+    });
+    // Activates the slicing-pipeline hook installed for the second slice below.
+    config.set_key_value("slicing_pipeline_plugin", new ConfigOptionStrings({"probe"}));
+
+    Print print;
+    Model model;
+    init_print({cube(20)}, print, model, config);
+    ModelObject *object_a = model.objects.front();
+    // add_object() gives the copy extruder 1, and objects only share slices when their configs match.
+    object_a->config.set_key_value("extruder", new ConfigOptionInt(1));
+    ModelObject *object_b = model.add_object(*object_a); // shares object_a's mesh
+    for (ModelInstance *instance : object_b->instances)
+        instance->set_offset(instance->get_offset() + Vec3d(40., 0., 0.));
+    // A per-object override makes the objects differ, so each slices itself.
+    object_a->config.set_key_value("sparse_infill_density", new ConfigOptionPercent(40));
+
+    print.apply(model, config);
+    print.process();
+    REQUIRE(print.objects().size() == 2);
+    // The non-const accessors hand out the layer vectors themselves, which the checks below compare.
+    PrintObject *print_b = print.get_object(1);
+    REQUIRE(print_b->model_object()->id() == object_b->id()); // Print slices its own copy of the model
+    REQUIRE(print_b->get_shared_object() == nullptr);
+    const LayerPtrs        own_layers         = print_b->layers();
+    const SupportLayerPtrs own_support_layers = print_b->support_layers();
+    REQUIRE(!own_layers.empty());
+    REQUIRE(!own_support_layers.empty());
+
+    // Without the override the objects are identical again: print_a redoes the steps the setting invalidated,
+    // and print_b shares it.
+    object_a->config.erase("sparse_infill_density");
+    print.apply(model, config);
+    REQUIRE(print.objects().size() == 2);
+    PrintObject *print_a = print.get_object(0);
+
+    // Erasing the override invalidates print_a's posPrepareInfill and the steps after it. Its hook is the first one
+    // print_a fires, and it runs after print_b starts sharing but before print_b takes the shared layers over.
+    bool hook_fired          = false;
+    bool shared_while_a_runs = false;
+    bool kept_layers         = false;
+    bool kept_support_layers = false;
+    {
+        Print::set_slicing_pipeline_hook_fn([&](Print &, const PrintObject *object, SlicingPipelineStepPlugin) {
+            if (object != print_a || hook_fired)
+                return;
+            hook_fired          = true;
+            shared_while_a_runs = print_b->get_shared_object() == print_a;
+            kept_layers         = print_b->layers() == own_layers;
+            kept_support_layers = print_b->support_layers() == own_support_layers;
+        });
+        const ScopeGuard reset_hook([] { Print::set_slicing_pipeline_hook_fn(nullptr); });
+        print.process();
+    }
+
+    REQUIRE(hook_fired);
+    CHECK(print.objects()[1] == print_b);
+    CHECK(shared_while_a_runs);
+    CHECK(kept_layers);
+    CHECK(kept_support_layers);
+    CHECK(print_b->get_shared_object() == print_a);
+    REQUIRE(!print_a->layers().empty());
+    CHECK(print_b->layers() == print_a->layers());
+    CHECK(print_b->support_layers() == print_a->support_layers());
+}
+
 // ---------------------------------------------------------------------------
 // Print::validate() warning collection
 //

tests/slic3rutils/CMakeLists.txt

@@ -37,6 +37,7 @@ add_executable(${_TEST_NAME}_tests
     test_plugin_json_depth.cpp
     test_shortcuts.cpp
     test_texture_color_palette.cpp
+    test_texture_island_view.cpp
     test_file_url.cpp
     test_user_manager.cpp
     ../fff_print/test_helpers.cpp

tests/slic3rutils/test_texture_island_view.cpp

@@ -0,0 +1,99 @@
+// How the texture displacement gizmo's view follows the UV editor's island highlight. The rules live in
+// libslic3r_gui; this is the suite that links it. Same Windows include prologue as
+// test_texture_color_palette.cpp (wx pulls in <windows.h>; keep WIN32_LEAN_AND_MEAN / NOMINMAX ahead of it).
+#ifdef WIN32
+    #ifndef WIN32_LEAN_AND_MEAN
+        #define WIN32_LEAN_AND_MEAN
+    #endif
+    #ifndef NOMINMAX
+        #define NOMINMAX
+    #endif
+    #include <Windows.h>
+#endif
+
+#include <catch2/catch_test_macros.hpp>
+#include <catch2/generators/catch_generators.hpp>
+
+#include "slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp"
+
+using Follow = Slic3r::GUI::GLGizmoTextureDisplacement::IslandViewFollow;
+
+namespace {
+
+// The View row's indices, and step()'s "apply nothing".
+constexpr int NORMAL = 0, FAST = 1, CHECKER = 2, DISTORTION = 3, NONE = -1;
+
+} // namespace
+
+TEST_CASE("a Normal view gives way to Fast while islands are selected and comes back once none are", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    CHECK(f.step(false, NORMAL, false) == NONE);
+    CHECK(f.step(true, NORMAL, false) == FAST);
+    CHECK(f.step(true, FAST, false) == NONE);
+    CHECK(f.step(false, FAST, false) == NORMAL);
+    CHECK(f.step(false, NORMAL, false) == NONE);
+}
+
+TEST_CASE("a Fast, Checker or Distortion view is left alone by the island highlight", "[TextureIslandView][TextureDisplacement]")
+{
+    const int view = GENERATE(FAST, CHECKER, DISTORTION);
+    Follow    f;
+    CHECK(f.step(true, view, false) == NONE);
+    CHECK(f.step(false, view, false) == NONE);
+}
+
+TEST_CASE("arriving in Normal with islands already selected switches to Fast", "[TextureIslandView][TextureDisplacement]")
+{
+    // The pane's Height button over Checker lands in Normal with the islands still selected.
+    Follow f;
+    CHECK(f.step(true, CHECKER, false) == NONE);
+    CHECK(f.step(true, NORMAL, false) == FAST);
+    CHECK(f.step(false, FAST, false) == NORMAL);
+}
+
+TEST_CASE("Normal picked while islands are selected stays until they are deselected", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    REQUIRE(f.step(true, NORMAL, false) == FAST);
+    f.picked(NORMAL);
+    CHECK(f.step(true, NORMAL, false) == NONE);
+    // A debug stage opening and closing over it changes nothing.
+    CHECK(f.step(true, NORMAL, true) == NONE);
+    CHECK(f.step(true, NORMAL, false) == NONE);
+    CHECK(f.step(false, NORMAL, false) == NONE);
+    CHECK(f.step(true, NORMAL, false) == FAST);
+}
+
+TEST_CASE("Fast picked while it was switched on stays after deselecting", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    REQUIRE(f.step(true, NORMAL, false) == FAST);
+    f.picked(FAST);
+    CHECK(f.step(false, FAST, false) == NONE);
+}
+
+TEST_CASE("Normal picked with nothing selected does not hold off the next switch", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    CHECK(f.step(false, NORMAL, false) == NONE);
+    f.picked(NORMAL);
+    CHECK(f.step(true, NORMAL, false) == FAST);
+}
+
+TEST_CASE("a debug stage holds Normal while it is open, and the switch follows once it closes", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    REQUIRE(f.step(true, NORMAL, false) == FAST);
+    // The stage takes Normal itself, with the islands still selected.
+    CHECK(f.step(true, NORMAL, true) == NONE);
+    CHECK(f.step(true, NORMAL, false) == FAST);
+}
+
+TEST_CASE("islands deselected while a debug stage is open apply no view over it", "[TextureIslandView][TextureDisplacement]")
+{
+    Follow f;
+    REQUIRE(f.step(true, NORMAL, false) == FAST);
+    CHECK(f.step(false, NORMAL, true) == NONE);
+    CHECK(f.step(false, NORMAL, false) == NONE);
+}