FDM painting gizmos (support/seam) now render object in neutral color

The goal is to ensure enough contrast independent on current filament color

src/slic3r/GUI/3DScene.cpp

@@ -306,6 +306,7 @@ const float GLVolume::MODEL_COLOR[4][4] = {
 };
 const float GLVolume::SLA_SUPPORT_COLOR[4] = { 0.75f, 0.75f, 0.75f, 1.0f };
 const float GLVolume::SLA_PAD_COLOR[4] = { 0.0f, 0.2f, 0.0f, 1.0f };
+const float GLVolume::NEUTRAL_COLOR[4] = { 0.9f, 0.9f, 0.9f, 1.0f };
 
 GLVolume::GLVolume(float r, float g, float b, float a)
     : m_transformed_bounding_box_dirty(true)
@@ -327,6 +328,7 @@ GLVolume::GLVolume(float r, float g, float b, float a)
     , is_extrusion_path(false)
     , force_transparent(false)
     , force_native_color(false)
+    , force_neutral_color(false)
     , tverts_range(0, size_t(-1))
     , qverts_range(0, size_t(-1))
 {
@@ -352,12 +354,16 @@ void GLVolume::set_render_color(const float* rgba, unsigned int size)
 
 void GLVolume::set_render_color()
 {
-    if (force_native_color)
+    if (force_native_color || force_neutral_color)
     {
         if (is_outside && shader_outside_printer_detection_enabled)
             set_render_color(OUTSIDE_COLOR, 4);
-        else
+        else {
+            if (force_native_color)
                 set_render_color(color, 4);
+            else
+                set_render_color(NEUTRAL_COLOR, 4);
+        }
     }
     else {
         if (hover == HS_Select)

src/slic3r/GUI/3DScene.hpp

@@ -251,6 +251,7 @@ public:
     static const float MODEL_COLOR[4][4];
     static const float SLA_SUPPORT_COLOR[4];
     static const float SLA_PAD_COLOR[4];
+    static const float NEUTRAL_COLOR[4];
 
     enum EHoverState : unsigned char
     {
@@ -336,6 +337,8 @@ public:
 	    bool                force_transparent : 1;
 	    // Whether or not always use the volume's own color (not using SELECTED/HOVER/DISABLED/OUTSIDE)
 	    bool                force_native_color : 1;
+        // Whether or not render this volume in neutral
+        bool                force_neutral_color : 1;
 	};
 
     // Is mouse or rectangle selection over this object to select/deselect it ?

src/slic3r/GUI/GLCanvas3D.cpp

@@ -1725,7 +1725,19 @@ void GLCanvas3D::toggle_model_objects_visibility(bool visible, const ModelObject
             if ((mo == nullptr || m_model->objects[vol->composite_id.object_id] == mo)
             && (instance_idx == -1 || vol->composite_id.instance_id == instance_idx)) {
                 vol->is_active = visible;
-                vol->force_native_color = (instance_idx != -1);
+
+                if (instance_idx == -1) {
+                    vol->force_native_color = false;
+                    vol->force_neutral_color = false;
+                } else {
+                    const GLGizmosManager& gm = get_gizmos_manager();
+                    auto gizmo_type = gm.get_current_type();
+                    if (gizmo_type == GLGizmosManager::FdmSupports
+                     || gizmo_type == GLGizmosManager::Seam)
+                        vol->force_neutral_color = true;
+                    else
+                        vol->force_native_color = true;
+                }
             }
         }
     }

src/slic3r/GUI/Gizmos/GLGizmoPainterBase.cpp

@@ -504,13 +504,13 @@ void TriangleSelectorGUI::render(ImGuiWrapper* imgui)
     m_iva_blockers.finalize_geometry(true);
 
     if (m_iva_enforcers.has_VBOs()) {
-        ::glColor4f(0.f, 0.f, 1.f, 0.2f);
+        ::glColor4f(0.f, 0.f, 1.f, 0.3f);
         m_iva_enforcers.render();
     }
 
 
     if (m_iva_blockers.has_VBOs()) {
-        ::glColor4f(1.f, 0.f, 0.f, 0.2f);
+        ::glColor4f(1.f, 0.f, 0.f, 0.3f);
         m_iva_blockers.render();
     }