Follow-up of 6194e67e68 - Separated the part that computed triangles normals and lighting inside the fragment shader into a separate shader mm_gouraud, which is only used for the multi-material painting gizmo.

src/slic3r/GUI/Gizmos/GLGizmoMmuSegmentation.cpp

@@ -174,6 +174,43 @@ void GLGizmoMmuSegmentation::set_painter_gizmo_data(const Selection &selection)
     }
 }
 
+void GLGizmoMmuSegmentation::render_triangles(const Selection &selection, const bool use_polygon_offset_fill) const
+{
+    ClippingPlaneDataWrapper clp_data = this->get_clipping_plane_data();
+    auto                    *shader   = wxGetApp().get_shader("mm_gouraud");
+    if (!shader)
+        return;
+    shader->start_using();
+    shader->set_uniform("clipping_plane", clp_data.clp_dataf);
+    shader->set_uniform("z_range", clp_data.z_range);
+    ScopeGuard guard([shader]() { if (shader) shader->stop_using(); });
+
+    const ModelObject *mo      = m_c->selection_info()->model_object();
+    int                mesh_id = -1;
+    for (const ModelVolume *mv : mo->volumes) {
+        if (!mv->is_model_part())
+            continue;
+
+        ++mesh_id;
+
+        const Transform3d trafo_matrix = mo->instances[selection.get_instance_idx()]->get_transformation().get_matrix() * mv->get_matrix();
+
+        bool is_left_handed = trafo_matrix.matrix().determinant() < 0.;
+        if (is_left_handed)
+            glsafe(::glFrontFace(GL_CW));
+
+        glsafe(::glPushMatrix());
+        glsafe(::glMultMatrixd(trafo_matrix.data()));
+
+        shader->set_uniform("volume_world_matrix", trafo_matrix);
+        m_triangle_selectors[mesh_id]->render(m_imgui);
+
+        glsafe(::glPopMatrix());
+        if (is_left_handed)
+            glsafe(::glFrontFace(GL_CCW));
+    }
+}
+
 static void render_extruders_combo(const std::string                       &label,
                                    const std::vector<std::string>          &extruders,
                                    const std::vector<std::array<float, 4>> &extruders_colors,
@@ -554,9 +591,7 @@ void TriangleSelectorMmGui::render(ImGuiWrapper *imgui)
     auto *shader = wxGetApp().get_current_shader();
     if (!shader)
         return;
-    assert(shader->get_name() == "gouraud");
-    ScopeGuard guard([shader]() { if (shader) shader->set_uniform("compute_triangle_normals_in_fs", false);});
-    shader->set_uniform("compute_triangle_normals_in_fs", true);
+    assert(shader->get_name() == "mm_gouraud");
 
     for (size_t color_idx = 0; color_idx < m_gizmo_scene.triangle_indices.size(); ++color_idx)
         if (m_gizmo_scene.has_VBOs(color_idx)) {
@@ -569,7 +604,7 @@ void TriangleSelectorMmGui::render(ImGuiWrapper *imgui)
         }
 
     if (m_paint_contour.has_VBO()) {
-        ScopeGuard guard_gouraud([shader]() { shader->start_using(); });
+        ScopeGuard guard_mm_gouraud([shader]() { shader->start_using(); });
         shader->stop_using();
 
         auto *contour_shader = wxGetApp().get_shader("mm_contour");

src/slic3r/GUI/Gizmos/GLGizmoMmuSegmentation.hpp

@@ -89,6 +89,8 @@ public:
 
     void set_painter_gizmo_data(const Selection& selection) override;
 
+    void render_triangles(const Selection& selection, bool use_polygon_offset_fill) const override;
+
     // TriangleSelector::serialization/deserialization has a limit to store 19 different states.
     // EXTRUDER_LIMIT + 1 states are used to storing the painting because also uncolored triangles are stored.
     // When increasing EXTRUDER_LIMIT, it needs to ensure that TriangleSelector::serialization/deserialization

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.cpp

@@ -43,12 +43,29 @@ void GLGizmoPainterBase::set_painter_gizmo_data(const Selection& selection)
     }
 }
 
+GLGizmoPainterBase::ClippingPlaneDataWrapper GLGizmoPainterBase::get_clipping_plane_data() const
+{
+    ClippingPlaneDataWrapper clp_data_out{{0.f, 0.f, 1.f, FLT_MAX}, {-FLT_MAX, FLT_MAX}};
+    // Take care of the clipping plane. The normal of the clipping plane is
+    // saved with opposite sign than we need to pass to OpenGL (FIXME)
+    if (bool clipping_plane_active = m_c->object_clipper()->get_position() != 0.; clipping_plane_active) {
+        const ClippingPlane *clp = m_c->object_clipper()->get_clipping_plane();
+        for (size_t i = 0; i < 3; ++i)
+            clp_data_out.clp_dataf[i] = -1.f * float(clp->get_data()[i]);
+        clp_data_out.clp_dataf[3] = float(clp->get_data()[3]);
+    }
 
+    // z_range is calculated in the same way as in GLCanvas3D::_render_objects(GLVolumeCollection::ERenderType type)
+    if (m_c->get_canvas()->get_use_clipping_planes()) {
+        const std::array<ClippingPlane, 2> &clps = m_c->get_canvas()->get_clipping_planes();
+        clp_data_out.z_range                     = {float(-clps[0].get_data()[3]), float(clps[1].get_data()[3])};
+    }
+
+    return clp_data_out;
+}
 
 void GLGizmoPainterBase::render_triangles(const Selection& selection, const bool use_polygon_offset_fill) const
 {
-    const ModelObject* mo = m_c->selection_info()->model_object();
-
     ScopeGuard offset_fill_guard([&use_polygon_offset_fill]() {
         if (use_polygon_offset_fill)
             glsafe(::glDisable(GL_POLYGON_OFFSET_FILL));
@@ -58,27 +75,17 @@ void GLGizmoPainterBase::render_triangles(const Selection& selection, const bool
         glsafe(::glPolygonOffset(-5.0, -5.0));
     }
 
-    // Take care of the clipping plane. The normal of the clipping plane is
-    // saved with opposite sign than we need to pass to OpenGL (FIXME)
-    bool clipping_plane_active = m_c->object_clipper()->get_position() != 0.;
-    float clp_dataf[4] = {0.f, 0.f, 1.f, FLT_MAX};
-    if (clipping_plane_active) {
-        const ClippingPlane* clp = m_c->object_clipper()->get_clipping_plane();
-        for (size_t i=0; i<3; ++i)
-            clp_dataf[i] = -1.f * float(clp->get_data()[i]);
-        clp_dataf[3] = float(clp->get_data()[3]);
-    }
-
     auto *shader = wxGetApp().get_shader("gouraud");
     if (! shader)
         return;
     shader->start_using();
     shader->set_uniform("slope.actived", false);
     shader->set_uniform("print_box.actived", false);
-    shader->set_uniform("clipping_plane", clp_dataf, 4);
+    shader->set_uniform("clipping_plane", this->get_clipping_plane_data().clp_dataf);
     ScopeGuard guard([shader]() { if (shader) shader->stop_using(); });
 
-    int mesh_id = -1;
+    const ModelObject *mo      = m_c->selection_info()->model_object();
+    int                mesh_id = -1;
     for (const ModelVolume* mv : mo->volumes) {
         if (! mv->is_model_part())
             continue;

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.hpp

@@ -126,7 +126,7 @@ public:
     virtual bool gizmo_event(SLAGizmoEventType action, const Vec2d& mouse_position, bool shift_down, bool alt_down, bool control_down);
 
 protected:
-    void render_triangles(const Selection& selection, const bool use_polygon_offset_fill = true) const;
+    virtual void render_triangles(const Selection& selection, bool use_polygon_offset_fill = true) const;
     void render_cursor() const;
     void render_cursor_circle() const;
     void render_cursor_sphere(const Transform3d& trafo) const;
@@ -176,6 +176,14 @@ protected:
         Right
     };
 
+    struct ClippingPlaneDataWrapper
+    {
+        std::array<float, 4> clp_dataf;
+        std::array<float, 2> z_range;
+    };
+
+    ClippingPlaneDataWrapper get_clipping_plane_data() const;
+
 private:
     bool is_mesh_point_clipped(const Vec3d& point, const Transform3d& trafo) const;
     void update_raycast_cache(const Vec2d& mouse_position,