Share the Estimated First-Layer Outline of the Wipe Tower

The preview brim, the placement margin and the pre-generation validation
warning each decided on their own whether the tower has a Type2 cone
base, reading the wall type and cone angle three different ways. The
preview's read cast the preset's enum to ConfigOptionEnum<T>, which a
preset-shaped config never holds, so the cone base was never previewed.

estimate_wipe_tower_first_layer_outline now answers that question once,
beside the footprint estimate, from the config and the resolved planner;
all three sites take the outline from it. The libslic3r case reads the
outline off a preset-shaped config, where the old cast came back empty.

src/libslic3r/GCode/WipeTowerEstimate.cpp

@@ -37,6 +37,17 @@ WipeTowerType resolve_wipe_tower_type(const ConfigBase &config)
     return type != nullptr ? WipeTowerType(type->getInt()) : WipeTowerType::Type2;
 }
 
+Polygon estimate_wipe_tower_first_layer_outline(const ConfigBase &config, WipeTowerType tower_type, double width, double depth, double height)
+{
+    // Type1 ignores the cone option. The wall type is read by value: a preset-shaped config
+    // holds it as ConfigOptionEnumGeneric, which a cast to ConfigOptionEnum<T> cannot see.
+    const ConfigOption *wall_type  = option_of(config, "wipe_tower_wall_type");
+    const ConfigOption *cone_angle = option_of(config, "wipe_tower_cone_angle");
+    const bool          cone       = tower_type == WipeTowerType::Type2 && wall_type != nullptr &&
+                         wall_type->getInt() == int(WipeTowerWallType::wtwCone) && cone_angle != nullptr;
+    return WipeTower2::cone_base_polygon(width, depth, height, cone ? cone_angle->getFloat() : 0.);
+}
+
 WipeTowerFootprint estimate_wipe_tower_footprint(const ConfigBase &config, WipeTowerType tower_type, const std::vector<unsigned int> &filament_ids, double layer_height, double max_object_height)
 {
     WipeTowerFootprint footprint;

src/libslic3r/GCode/WipeTowerEstimate.hpp

@@ -2,6 +2,8 @@
 
 #include <vector>
 
+#include "../Polygon.hpp"
+
 namespace Slic3r {
 
 class ConfigBase;
@@ -23,6 +25,12 @@ struct WipeTowerFootprint
 // the GUI and CLI placement can resolve it without a Print.
 WipeTowerType resolve_wipe_tower_type(const ConfigBase &config);
 
+// First-layer outline of an estimated tower in tower-local scaled coordinates, brim excluded:
+// the body box, or for a Type2 cone wall the box unioned with the cone's base. The preview,
+// the placement margin and validation all take the outline from here so they cannot disagree
+// about whether a cone exists.
+Polygon estimate_wipe_tower_first_layer_outline(const ConfigBase &config, WipeTowerType tower_type, double width, double depth, double height);
+
 // filament_ids:  0-based filaments purged on the plate. The config cannot see custom G-code tool
 //                changes, so ids derived from the model must include them
 //                (Print::extruders(true)) or a real tower is sized as if it were never built.

src/libslic3r/Print.cpp

@@ -1078,15 +1078,12 @@ static StringObjectException layered_print_cleareance_valid(const Print &print,
                                          convex_hulls_temp;
     Polygons tower_polys_estimated;
     if (!exact_footprint && !convex_hulls_temp.empty()) {
-        Polygon base = convex_hulls_temp.front();
-        if (config.wipe_tower_wall_type.value == WipeTowerWallType::wtwCone && print.wipe_tower_type() == WipeTowerType::Type2) {
-            double max_height = 0.;
-            for (const PrintObject *object : print.objects())
-                max_height = std::max(max_height, unscale_(object->size().z()));
-            base = WipeTower2::cone_base_polygon(width, depth, max_height, config.wipe_tower_cone_angle.value);
-            base.rotate(Geometry::deg2rad(a));
-            base.translate(Point(scale_(x), scale_(y)));
-        }
+        double max_height = 0.;
+        for (const PrintObject *object : print.objects())
+            max_height = std::max(max_height, unscale_(object->size().z()));
+        Polygon base = estimate_wipe_tower_first_layer_outline(config, print.wipe_tower_type(), width, depth, max_height);
+        base.rotate(Geometry::deg2rad(a));
+        base.translate(Point(scale_(x), scale_(y)));
         tower_polys_estimated = offset(base, float(scale_(brim_width)));
     }
     // Object proximity stays a body-only warning: brim near-misses would newly warn on