From b8590180d8152844e8709063d3fe048dec305c1c Mon Sep 17 00:00:00 2001
From: bubnikv <bubnikv@gmail.com>
Date: Tue, 8 Nov 2016 15:33:13 +0100
Subject: [PATCH] Fix of https://github.com/prusa3d/Slic3r/issues/20 Slicing
 preview incorrect in terms of visible solid layers

---
 lib/Slic3r/GUI/3DScene.pm          | 22 ++++++++++------------
 lib/Slic3r/GUI/Plater/3DPreview.pm | 13 +++++++------
 2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/lib/Slic3r/GUI/3DScene.pm b/lib/Slic3r/GUI/3DScene.pm
index 889dc0741..8c737bcab 100644
--- a/lib/Slic3r/GUI/3DScene.pm
+++ b/lib/Slic3r/GUI/3DScene.pm
@@ -978,32 +978,30 @@ sub draw_volumes {
         }
 
         my $qverts_begin = 0;
-        my $qverts_end = defined($volume->qverts) ? $volume->qverts->size() : 0;
+        my $qverts_end   = defined($volume->qverts) ? $volume->qverts->size() : 0;
         my $tverts_begin = 0;
-        my $tverts_end = defined($volume->tverts) ? $volume->tverts->size() : 0;
-        if ($volume->range && $volume->offsets && @{$volume->offsets}) {
+        my $tverts_end   = defined($volume->tverts) ? $volume->tverts->size() : 0;
+        my $n_offsets    = ($volume->range && $volume->offsets) ? scalar(@{$volume->offsets}) : 0;
+        if ($n_offsets) {
             # The Z layer range is specified.
             # First test whether the Z span of this object is not out of ($min_z, $max_z) completely.
             my ($min_z, $max_z) = @{$volume->range};
             next if ($volume->offsets->[0] > $max_z || $volume->offsets->[-3] < $min_z);
             # Then find the lowest layer to be displayed.
             my $i = 0;
-            while ($i < @{$volume->offsets} && $volume->offsets->[$i] < $min_z) {
+            while ($i < $n_offsets && $volume->offsets->[$i] < $min_z) {
                 $i += 3;
             }
             # This shall not happen.
-            next if ($i == @{$volume->offsets});
+            next if ($i == $n_offsets);
             # Remember start of the layer.
-            if ($i >= 3) {
-                # Get end of the preceding layer, which is the start of the current layer.
-                $qverts_begin = $volume->offsets->[$i-2];
-                $tverts_begin = $volume->offsets->[$i-1];
-            }
+            $qverts_begin = $volume->offsets->[$i+1];
+            $tverts_begin = $volume->offsets->[$i+2];
             # Some layers are above $min_z. Which?
-            while ($i < @{$volume->offsets} && $volume->offsets->[$i] <= $max_z) {
+            while ($i < $n_offsets && $volume->offsets->[$i] <= $max_z) {
                 $i += 3;
             }
-            if ($i < @{$volume->offsets}) {
+            if ($i < $n_offsets) {
                 $qverts_end = $volume->offsets->[$i+1];
                 $tverts_end = $volume->offsets->[$i+2];
             }
diff --git a/lib/Slic3r/GUI/Plater/3DPreview.pm b/lib/Slic3r/GUI/Plater/3DPreview.pm
index fde9ef131..d452f60cf 100644
--- a/lib/Slic3r/GUI/Plater/3DPreview.pm
+++ b/lib/Slic3r/GUI/Plater/3DPreview.pm
@@ -145,14 +145,15 @@ sub load_print {
         }
         $self->enabled(1);
         $self->{layers_z} = [ sort { $a <=> $b } keys %z ];
-        $self->slider_low->SetRange(0, scalar(@{$self->{layers_z}})-1);
-        $self->slider_high->SetRange(0, scalar(@{$self->{layers_z}})-1);
+        my $num_layers = scalar(@{$self->{layers_z}});
+        $self->slider_low->SetRange(0, $num_layers-1);
+        $self->slider_high->SetRange(0, $num_layers-1);
         $self->slider_low->SetValue(0);
-        if (($z_idx = $self->slider_high->GetValue) <= $#{$self->{layers_z}} && $self->slider_high->GetValue != 0) {
+        if (($z_idx = $self->slider_high->GetValue) < $num_layers && $self->slider_high->GetValue != 0) {
             # use $z_idx
         } else {
-            $self->slider_high->SetValue(scalar(@{$self->{layers_z}})-1);
-            $z_idx = @{$self->{layers_z}} ? -1 : undef;
+            $self->slider_high->SetValue($num_layers-1);
+            $z_idx = $num_layers ? ($num_layers-1) : undef;
         }
         $self->slider_low->Show;
         $self->slider_high->Show;
@@ -184,7 +185,7 @@ sub set_z_range
     return if !$self->enabled;
     $self->{z_label_low}->SetLabel(sprintf '%.2f', $z_low);
     $self->{z_label_high}->SetLabel(sprintf '%.2f', $z_high);
-    $self->canvas->set_toolpaths_range($z_low, $z_high);
+    $self->canvas->set_toolpaths_range($z_low-1e-5, $z_high+1e-5);
     $self->canvas->Refresh if $self->IsShown;
 }