From 8db68fc5e3db7fe105e3366e27fcd7654a4795a4 Mon Sep 17 00:00:00 2001
From: artemp <artem@mapnik.org>
Date: Thu, 21 Aug 2014 12:43:43 +0100
Subject: [PATCH] hextree - avoid quantizing images with less than 3 pixels
 (hextree implementation requirement)

---
 include/mapnik/png_io.hpp | 61 +++++++++++++++++++++------------------
 1 file changed, 33 insertions(+), 28 deletions(-)

diff --git a/include/mapnik/png_io.hpp b/include/mapnik/png_io.hpp
index 5d338dabc..3df3197a4 100644
--- a/include/mapnik/png_io.hpp
+++ b/include/mapnik/png_io.hpp
@@ -654,40 +654,45 @@ void save_as_png8_hex(T1 & file,
 {
     unsigned width = image.width();
     unsigned height = image.height();
-
-    // structure for color quantization
-    hextree<mapnik::rgba> tree(opts.colors);
-    if (opts.trans_mode >= 0)
+    if (width + height > 3) // at least 3 pixels (hextree implementation requirement)
     {
-        tree.setTransMode(opts.trans_mode);
-    }
-    if (opts.gamma > 0)
-    {
-        tree.setGamma(opts.gamma);
-    }
-
-    for (unsigned y = 0; y < height; ++y)
-    {
-        typename T2::pixel_type const * row = image.getRow(y);
-        for (unsigned x = 0; x < width; ++x)
+        // structure for color quantization
+        hextree<mapnik::rgba> tree(opts.colors);
+        if (opts.trans_mode >= 0)
         {
-            unsigned val = row[x];
-            tree.insert(mapnik::rgba(U2RED(val), U2GREEN(val), U2BLUE(val), U2ALPHA(val)));
+            tree.setTransMode(opts.trans_mode);
+        }
+        if (opts.gamma > 0)
+        {
+            tree.setGamma(opts.gamma);
         }
-    }
 
-    //transparency values per palette index
-    std::vector<mapnik::rgba> pal;
-    tree.create_palette(pal);
-    std::vector<mapnik::rgb> palette;
-    std::vector<unsigned> alphaTable;
-    for (unsigned i=0; i<pal.size(); ++i)
+        for (unsigned y = 0; y < height; ++y)
+        {
+            typename T2::pixel_type const * row = image.getRow(y);
+            for (unsigned x = 0; x < width; ++x)
+            {
+                unsigned val = row[x];
+                tree.insert(mapnik::rgba(U2RED(val), U2GREEN(val), U2BLUE(val), U2ALPHA(val)));
+            }
+        }
+
+        //transparency values per palette index
+        std::vector<mapnik::rgba> pal;
+        tree.create_palette(pal);
+        std::vector<mapnik::rgb> palette;
+        std::vector<unsigned> alphaTable;
+        for (unsigned i=0; i<pal.size(); ++i)
+        {
+            palette.push_back(rgb(pal[i].r, pal[i].g, pal[i].b));
+            alphaTable.push_back(pal[i].a);
+        }
+        save_as_png8<T1, T2, hextree<mapnik::rgba> >(file, image, tree, palette, alphaTable, opts);
+    }
+    else
     {
-        palette.push_back(rgb(pal[i].r, pal[i].g, pal[i].b));
-        alphaTable.push_back(pal[i].a);
+        throw std::runtime_error("Can't quantize images with less than 3 pixels");
     }
-
-    save_as_png8<T1, T2, hextree<mapnik::rgba> >(file, image, tree, palette, alphaTable, opts);
 }
 
 template <typename T1, typename T2>