Fix of #7711, #7903, #8044 (wipe tower refusing to slice when layer height modifier is used):

Same settings of the layer height modifier does not guarantee to always produce profiles
exactly equal numerically. This is broken since 71ba15b.

src/libslic3r/Print.cpp

@@ -537,7 +537,19 @@ std::string Print::validate(std::string* warning) const
                 for (size_t idx_object = 0; idx_object < m_objects.size(); ++ idx_object) {
                     if (idx_object == tallest_object_idx)
                         continue;
-                    if (layer_height_profiles[idx_object] != layer_height_profiles[tallest_object_idx])
+                    // Check that the layer height profiles are equal. This will happen when one object is
+                    // a copy of another, or when a layer height modifier is used the same way on both objects.
+                    // The latter case might create a floating point inaccuracy mismatch, so compare
+                    // element-wise using an epsilon check.
+                    bool profiles_equal = layer_height_profiles[idx_object].size() == layer_height_profiles[tallest_object_idx].size();
+                    size_t i = 0;
+                    const coordf_t eps = 0.5 * EPSILON; // layers closer than EPSILON will be merged later. Let's make
+                    // this check a bit more sensitive to make sure we never consider two different layers as one.
+                    while (profiles_equal && i < layer_height_profiles[idx_object].size()) {
+                        profiles_equal = (std::abs(layer_height_profiles[idx_object][i] - layer_height_profiles[tallest_object_idx][i]) < eps);
+                        ++i;
+                    }
+                    if (! profiles_equal)
                         return L("The Wipe tower is only supported if all objects have the same variable layer height");
                 }
             }