feat: a real dropper that reads the model, foldable sections, a scrolling panel

- The dropper has its own pipette icon instead of borrowing the placement
  handle's, drawn in the house style: 16 px canvas, 0.4 stroke in #949494,
  teal on the tip, which is the part that carries the meaning.

- It picks off the model as well as off the preview. A click on the 3D view
  while it is armed reads the picture's own colour at that point, through
  the same projection the bake uses, not the pixel on screen: the screen
  pixel carries the lighting and the filament the colour was already
  quantized to, so keying on it would remove the wrong thing. The patch
  frame comes from extract_painted_patch() plus
  texture_displacement_patch_frame(), so a cylindrical or spherical layer
  reads at the same place the bake will.

- Placement, Color and Background fold away, with the triangle-and-text the
  displacement panel's "More settings" link uses rather than ImGui's own
  filled bar, which is louder than anything else in this window. Folded,
  Background still says whether it is removing anything. Open by default and
  remembered for the session only: this is panel state, not something a
  project should carry.

- The body scrolls and the footer is pinned under it, the shape the
  displacement panel already uses. With the panel this tall, Apply and Close
  were the first things to go off the bottom of a short canvas.

resources/images/texture_displacement_pipette.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><g transform="rotate(-45 8 8)"><path d="M8 14.4 6.5 11.2 9.5 11.2 Z" style="fill:#009688"/><path d="M6.5 7.3 6.5 11.2 8 14.4 9.5 11.2 9.5 7.3" style="fill:none;stroke:#949494;stroke-width:0.4;stroke-linejoin:round;stroke-linecap:round"/><rect x="5.5" y="3.8" width="5" height="3.5" rx="0.9" style="fill:none;stroke:#949494;stroke-width:0.4;stroke-linejoin:round"/></g></svg>

src/slic3r/GUI/Gizmos/GLGizmoImage.cpp

@@ -4,6 +4,7 @@
 #include "libslic3r/TextureDisplacement.hpp"
 #include "libslic3r/format.hpp"
 
+#include "slic3r/GUI/Camera.hpp"
 #include "slic3r/GUI/GLCanvas3D.hpp"
 #include "slic3r/GUI/GLTexture.hpp"
 #include "slic3r/GUI/GUI.hpp"
@@ -55,6 +56,58 @@ wxString GLGizmoImage::handle_snapshot_action_name(bool shift_down, GLGizmoPaint
     return erasing ? _L("Remove image from the area") : _L("Place image");
 }
 
+bool GLGizmoTextureDisplacement::pick_background_at(const Vec2d &mouse_pos)
+{
+    ModelVolume              *mv    = texture_volume();
+    ModelObject              *mo    = m_c->selection_info()->model_object();
+    TextureDisplacementLayer *layer = mv != nullptr ? active_layer() : nullptr;
+    if (mv == nullptr || mo == nullptr || layer == nullptr || layer->empty())
+        return false;
+
+    const int idx = texture_volume_raycaster_index();
+    if (idx < 0)
+        return false;
+    const Selection  &selection = m_parent.get_selection();
+    const Transform3d trafo = mo->instances[selection.get_instance_idx()]->get_transformation().get_matrix() * mv->get_matrix();
+    const Camera     &camera = wxGetApp().plater()->get_camera();
+
+    Vec3f hit = Vec3f::Zero(), normal = Vec3f::Zero();
+    if (!m_c->raycaster()->raycasters()[size_t(idx)]->unproject_on_mesh(
+            mouse_pos, trafo, camera, hit, normal,
+            m_c->object_clipper()->get_clipping_plane()))
+        return false;
+
+    // The picture's own colour at that point, read through the projection the bake uses, rather
+    // than the pixel on screen: the screen pixel carries the lighting and the filament the colour
+    // was already quantized to, so keying on it would remove the wrong thing.
+    //
+    // Uncorrected, deliberately. The key is applied at the end of the correction chain, against
+    // colours the earlier passes have already moved, so it has to be stated in those terms - the
+    // same reason the panel's dropper reads the corrected preview.
+    const indexed_triangle_set &base = mv->mesh().its;
+    const indexed_triangle_set  patch =
+        extract_painted_patch(base, mv->texture_displacement_facet(layer->slot).get_data());
+    Vec3f center = Vec3f::Zero(), axis = Vec3f::UnitZ(), average_normal = Vec3f::UnitZ();
+    if (!patch.indices.empty())
+        texture_displacement_patch_frame(patch, texture_displacement_vertex_normals(base), center, axis,
+                                         average_normal);
+
+    DecodedHeightTexture tex = decode_height_texture(*layer);
+    apply_color_adjustments(tex, *layer);
+    Vec3f rgb;
+    if (!sample_layer_color(tex, *layer, hit, normal, rgb, center, axis))
+        return false;
+
+    for (int c = 0; c < 3; ++c)
+        layer->bg_color[c] = std::clamp(rgb[c], 0.f, 1.f);
+    layer->bg_from_corners = false;
+    layer->bg_remove       = true;
+    m_image_bg_picking     = false;
+    m_preview_params_dirty = true;
+    m_parent.set_as_dirty();
+    return true;
+}
+
 void GLGizmoTextureDisplacement::set_file_drag_over(bool over)
 {
     if (!image_mode() || m_file_drag_over == over)
@@ -209,6 +262,8 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
     ImGuiWrapper::push_toolbar_style(m_parent.get_scale());
     GizmoImguiBegin(get_name(), flags);
     ensure_panel_icons();
+    const float previous_body_h   = m_panel_body_h;
+    const float previous_footer_h = m_panel_footer_h;
 
     const ImGuiStyle &style    = ImGui::GetStyle();
     const bool        busy     = m_bake_in_progress || m_prepare_in_progress;
@@ -260,6 +315,31 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
         hover_tip(tip_text);
         return clicked;
     };
+    // A section header that folds its contents away. ImGui's own CollapsingHeader draws a filled bar
+    // that is louder than anything else in this window, so this is the same triangle-and-text the
+    // displacement panel's "More settings" link uses, at heading weight.
+    const auto section = [&](const char *id, const wxString &label, bool &open) {
+        const float  arrow = std::round(ImGui::GetFontSize() * 0.55f);
+        const ImVec2 ts    = ImGui::CalcTextSize(label.ToUTF8().data());
+        const ImVec2 p     = ImGui::GetCursorScreenPos();
+        ImGui::PushID(id);
+        if (ImGui::InvisibleButton("##sec", ImVec2(panel_w, ts.y + gap_s)))
+            open = !open;
+        const bool  hot = ImGui::IsItemHovered();
+        ImDrawList *dl  = ImGui::GetWindowDrawList();
+        const ImU32 col = ImGui::GetColorU32(hot ? ImGuiCol_Text : ImGuiCol_TextDisabled);
+        const float cx = p.x + 0.5f * arrow, cy = p.y + 0.5f * ts.y, hs = 0.32f * arrow;
+        if (open)
+            dl->AddTriangleFilled(ImVec2(cx - hs, cy - 0.5f * hs), ImVec2(cx + hs, cy - 0.5f * hs),
+                                  ImVec2(cx, cy + 0.5f * hs), col);
+        else
+            dl->AddTriangleFilled(ImVec2(cx - 0.5f * hs, cy - hs), ImVec2(cx - 0.5f * hs, cy + hs),
+                                  ImVec2(cx + 0.5f * hs, cy), col);
+        dl->AddText(ImVec2(p.x + arrow + gap_s, p.y), col, label.ToUTF8().data());
+        ImGui::PopID();
+        return open;
+    };
+
     // The integer twin of float_row, for the colour count.
     const auto int_row = [&](const char *id, const wxString &label, int *v, int v_min, int v_max,
                              const char *format) -> bool {
@@ -314,6 +394,25 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
     }
     ImGui::Separator();
 
+    // Everything between the title and the footer scrolls as one, so Apply and Close stay on screen
+    // on a short canvas instead of being the first thing pushed off the bottom. Sized from last
+    // frame's content and footer heights, as the displacement panel's body is.
+    const float bottom     = m_undocked ? ImGui::GetIO().DisplaySize.y : bottom_limit;
+    const float max_body_h = std::max(m_imgui->scaled(8.f), bottom - ImGui::GetCursorScreenPos().y -
+                                                                m_panel_footer_h - style.WindowPadding.y -
+                                                                style.ItemSpacing.y);
+    const float body_h      = m_panel_body_h > 0.f ? std::min(m_panel_body_h + 1.f, max_body_h) : max_body_h;
+    const float scrollbar_w = m_imgui->scaled(0.5f);
+    const ImVec4 grab       = wxGetApp().dark_mode() ? ImVec4(1.f, 1.f, 1.f, 0.26f) : ImVec4(0.f, 0.f, 0.f, 0.26f);
+    ImGui::PushStyleVar(ImGuiStyleVar_ScrollbarSize, scrollbar_w);
+    ImGui::PushStyleVar(ImGuiStyleVar_ScrollbarRounding, 0.5f * scrollbar_w);
+    ImGui::PushStyleColor(ImGuiCol_ScrollbarBg, ImVec4(0.f, 0.f, 0.f, 0.f));
+    ImGui::PushStyleColor(ImGuiCol_ScrollbarGrab, grab);
+    ImGui::PushStyleColor(ImGuiCol_ScrollbarGrabHovered, ImVec4(grab.x, grab.y, grab.z, 0.45f));
+    ImGui::PushStyleColor(ImGuiCol_ScrollbarGrabActive, ImVec4(grab.x, grab.y, grab.z, 0.65f));
+    ImGui::PushStyleColor(ImGuiCol_ChildBg, ImVec4(0.f, 0.f, 0.f, 0.f));
+    ImGui::BeginChild("##image_body", ImVec2(panel_w, body_h), false);
+
     // The picture, shown whole and the full width of the window: it is the thing being placed, so a
     // row-sized thumbnail beside a file name is the wrong size for it. Clicking it opens the library,
     // which is also where Import lives, and before anything is loaded the same box is an empty frame
@@ -377,7 +476,7 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
             box_hit = ImGui::Button("?##thumb", ImVec2(panel_w, box_h));
         }
         hover_tip(m_image_bg_picking ?
-                      _u8L("Click the part of the picture that is its background.") :
+                      _u8L("Click the background, here or on the model.") :
                       _u8L("Choose a different picture. Where you placed it and how it is corrected stay as "
                            "they are."));
         if (box_hit) {
@@ -428,6 +527,7 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
                        "flatter than this, and stops at a sharper fold. Small values keep it to one face."));
 
         ImGui::Separator();
+        if (section("place", _L("Placement"), m_image_sec_place)) {
 
         // Projection, minus Unwrap: that one is an editor's worth of UI (seams, islands, the UV pane)
         // for a tool whose whole point is a click and a few sliders.
@@ -548,7 +648,10 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
             }
         }
 
+        } // Placement
+
         ImGui::Separator();
+        if (section("color", _L("Color"), m_image_sec_color)) {
 
         // Colour correction. Every one of these changes which filament each area lands in, which is
         // why they are here rather than left to whatever the file happened to contain: a photo that
@@ -588,6 +691,14 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
                            "actually made of, not an even split of the range. Off leaves it alone."));
         }
 
+        } // Color
+
+        ImGui::Separator();
+        if (!section("bg", _L("Background"), m_image_sec_bg)) {
+            // Folded away, but still worth saying whether it is doing anything.
+            ImGui::SameLine();
+            ImGui::TextDisabled("%s", layer->bg_remove ? _u8L("removed").c_str() : _u8L("kept").c_str());
+        } else {
         if (m_imgui->bbl_checkbox(_L("Remove background"), layer->bg_remove))
             m_preview_params_dirty = true;
         hover_tip(_u8L("Leaves the background unprinted, so the object's own color shows through instead of "
@@ -632,8 +743,9 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
                                "plain card. Click to choose a color yourself instead.") :
                           _u8L("The color being removed. Click to change it."));
             ImGui::SameLine(0.f, gap_s);
-            if (icon_toggle(930, "texture_displacement_adjust.svg", m_image_bg_picking, _L("Pick from the picture"),
-                            _L("Pick from the picture - then click the background in the preview above.")))
+                if (icon_toggle(930, "texture_displacement_pipette.svg", m_image_bg_picking, _L("Pick the color"),
+                            _L("Pick the color - then click the background, either in the preview above or on "
+                               "the model itself.")))
                 m_image_bg_picking = !m_image_bg_picking;
             if (!layer->bg_from_corners) {
                 ImGui::SameLine(0.f, gap_s);
@@ -649,6 +761,8 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
                            "shadow or a gradient is left behind; lower it when it starts eating the picture."));
         }
 
+        } // Background
+
         if (m_imgui->bbl_checkbox(_L("Negative"), layer->color_invert))
             m_preview_params_dirty = true;
         hover_tip(_u8L("Prints the picture inverted, light for dark and each color for its opposite."));
@@ -687,6 +801,12 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
         m_preview_params_dirty = false;
     }
 
+    m_panel_body_h = ImGui::GetCursorPosY() - style.ItemSpacing.y;
+    ImGui::EndChild();
+    ImGui::PopStyleColor(5);
+    ImGui::PopStyleVar(2);
+
+    const float footer_top = ImGui::GetCursorScreenPos().y;
     ImGui::Separator();
     {
         const bool painted   = placed;
@@ -745,6 +865,12 @@ void GLGizmoTextureDisplacement::render_image_input_window(float x, float y, flo
         }
     }
 
+    m_panel_footer_h = ImGui::GetCursorScreenPos().y - footer_top;
+    // Both heights feed back into next frame's layout, so the window needs one more frame whenever
+    // either of them moved.
+    if (std::abs(m_panel_body_h - previous_body_h) > 0.5f || std::abs(m_panel_footer_h - previous_footer_h) > 0.5f)
+        m_parent.request_extra_frame();
+
     // Last, on the foreground list, so it covers the panel as well as the view.
     render_image_drop_hint();
 

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -771,6 +771,11 @@ bool GLGizmoTextureDisplacement::on_mouse(const wxMouseEvent &mouse_event)
 {
     if (m_seam_edit_mode)
         return on_mouse_seam(mouse_event);
+    // The background dropper takes the next click wherever it lands, the model included, so it comes
+    // before both the handle and the paint.
+    if (m_image_bg_picking && mouse_event.LeftDown() &&
+        pick_background_at(Vec2d(mouse_event.GetX(), mouse_event.GetY())))
+        return true;
     if (m_adjust_texture_mode) {
         if (on_mouse_adjust_texture(mouse_event))
             return true;
@@ -3704,7 +3709,8 @@ void GLGizmoTextureDisplacement::ensure_panel_icons()
         "texture_displacement_add.svg", "texture_displacement_add_negative.svg", "circle_paint.svg",
         "menu_obj_sphere.svg", "menu_obj_cube.svg", "menu_obj_cylinder.svg", "texture_displacement_map_unwrap.svg",
         "texture_displacement_map_view.svg", "texture_displacement_tile_repeat.svg", "menu_mirror_x.svg",
-        "texture_displacement_adjust.svg", "canvas_drag.svg", "texture_displacement_move_up.svg",
+        "texture_displacement_adjust.svg", "texture_displacement_pipette.svg", "canvas_drag.svg",
+        "texture_displacement_move_up.svg",
         "texture_displacement_move_down.svg", "texture_displacement_drag.svg",
         "texture_displacement_select_all.svg", "texture_displacement_erase_all.svg",
     };

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp

@@ -330,6 +330,15 @@ private:
     // Set while the panel's background dropper is armed: the next click on the picture preview takes
     // the colour under it instead of opening the library.
     bool m_image_bg_picking = false;
+    // Takes the background colour from the point of the model under `mouse_pos`: the picture's own
+    // colour there, read through the same projection the bake uses, not the lit pixel on screen.
+    // False when the ray misses or the layer does not colour that point, leaving the dropper armed.
+    bool pick_background_at(const Vec2d &mouse_pos);
+    // Which of the Image panel's sections are unfolded. Panel state for the session, deliberately
+    // not saved with the project.
+    bool m_image_sec_place = true;
+    bool m_image_sec_color = true;
+    bool m_image_sec_bg    = true;
     // Standard mode's Bake: remesh to an even density, refine where the texture bends, then displace.
     // The order matters and is the whole reason this is one button - a height map can only move
     // existing vertices, so the mesh has to be prepared first, and remeshing after painting would drop