From 2a31f5e6fc81438984bd28de707505458d817b9f Mon Sep 17 00:00:00 2001
From: tamasmeszaros <meszaros.q@gmail.com>
Date: Mon, 26 Nov 2018 15:03:57 +0100
Subject: [PATCH] Refinement of the slice index interface

---
 src/libslic3r/SLAPrint.cpp | 10 ++++++++++
 src/libslic3r/SLAPrint.hpp |  6 +++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/libslic3r/SLAPrint.cpp b/src/libslic3r/SLAPrint.cpp
index a40aebc45..605391a9d 100644
--- a/src/libslic3r/SLAPrint.cpp
+++ b/src/libslic3r/SLAPrint.cpp
@@ -564,6 +564,8 @@ void SLAPrint::process()
     // layers according to quantized height levels
     std::map<LevelID, LayerRefs> levels;
 
+    // We have the layer polygon collection but we need to unite them into
+    // an index where the key is the height level in discrete levels (clipper)
     auto index_slices = [this, ilh, ilhd, &levels](SLAPrintObject& po) {
         auto sih = LevelID(scale_(ilh));
 
@@ -606,11 +608,18 @@ void SLAPrint::process()
             }
         }
 
+        // shortcut for empty index into the slice vectors
+        static const auto EMPTY_SLICE = SLAPrintObject::SliceRecord::NONE;
+
         for(int i = 0; i < oslices.size(); ++i) {
             LevelID h = levelids[i];
             auto& lyrs = levels[h]; // this initializes a new record
             lyrs.emplace_back(oslices[i], po.m_instances);
+
+            // now for the public slice index:
             SLAPrintObject::SliceRecord& sr = po.m_slice_index[h];
+            // There should be only one slice layer for each print object
+            assert(sr.model_slices_idx == EMPTY_SLICE);
             sr.model_slices_idx = i;
         }
 
@@ -625,6 +634,7 @@ void SLAPrint::process()
                 lyrs.emplace_back(sslices[i], po.m_instances);
 
                 SLAPrintObject::SliceRecord& sr = po.m_slice_index[h];
+                assert(sr.support_slices_idx == EMPTY_SLICE);
                 sr.support_slices_idx = i;
             }
         }
diff --git a/src/libslic3r/SLAPrint.hpp b/src/libslic3r/SLAPrint.hpp
index 1f6695dbf..88b207d82 100644
--- a/src/libslic3r/SLAPrint.hpp
+++ b/src/libslic3r/SLAPrint.hpp
@@ -87,12 +87,16 @@ public:
     const std::vector<ExPolygons>& get_model_slices() const;
     const std::vector<ExPolygons>& get_support_slices() const;
 
+    // An index record referencing the slices
+    // (get_model_slices(), get_support_slices()) where the keys are the height
+    // levels of the model in scaled-clipper coordinates. The levels correspond
+    // to the z coordinate of the object coordinate system.
     struct SliceRecord {
         using Key = long long;
         inline static float scale_back(Key h) { return float(scale_(h)); }
 
         using Idx = size_t;
-        static const Idx NONE = ULONG_MAX; // std::numeric_limits<Idx>::max() // damn msvc 2013... ;
+        static const Idx NONE = Idx(-1); // this will be the max limit of size_t
 
         Idx model_slices_idx = NONE;
         Idx support_slices_idx = NONE;