customization to agg 2.4 span_image_resample_rgba_affine

custom_span_vs_agg24_orig.diff

diff --git a/include/mapnik/span_image_filter.hpp b/include/mapnik/span_image_filter.hpp
index e32b5a2..a4f8159 100644
--- a/include/mapnik/span_image_filter.hpp
+++ b/include/mapnik/span_image_filter.hpp
@@ -29,7 +29,7 @@ using namespace agg;
 
 template<class Source> 
 class span_image_resample_rgba_affine : 
-        public span_image_resample_affine<Source>
+public span_image_resample_affine<Source>
 {
 public:
     typedef Source source_type;
@@ -71,7 +71,7 @@ public:
             (diameter * base_type::m_rx + image_subpixel_mask) >> 
                 image_subpixel_shift;
 
-        const boost::int16_t* weight_array = base_type::filter().weight_array();
+        const int16* weight_array = base_type::filter().weight_array();
 
         do
         {
@@ -108,8 +108,7 @@ public:
                     fg[0] += *fg_ptr++ * weight;
                     fg[1] += *fg_ptr++ * weight;
                     fg[2] += *fg_ptr++ * weight;
-                    fg[3] += *fg_ptr   * weight;
-
+                    fg[3] += *fg_ptr++ * weight;
                     total_weight += weight;
                     x_hr  += base_type::m_rx_inv;
                     if(x_hr >= filter_scale) break;
@@ -120,30 +119,20 @@ public:
                 fg_ptr = (const value_type*)base_type::source().next_y();
             }
 
-            if (total_weight)
-            {
-                fg[3] /= total_weight;
             fg[0] /= total_weight;
             fg[1] /= total_weight;
             fg[2] /= total_weight;
+            fg[3] /= total_weight;
 
             if(fg[0] < 0) fg[0] = 0;
             if(fg[1] < 0) fg[1] = 0;
             if(fg[2] < 0) fg[2] = 0;
             if(fg[3] < 0) fg[3] = 0;
-            }
-            else
-            {
-                fg[0] = 0;
-                fg[1] = 0;
-                fg[2] = 0;
-                fg[3] = 0;
-            }
 
-            if(fg[order_type::R] > base_mask)         fg[order_type::R] = base_mask;
-            if(fg[order_type::G] > base_mask)         fg[order_type::G] = base_mask;
-            if(fg[order_type::B] > base_mask)         fg[order_type::B] = base_mask;
             if(fg[order_type::A] > base_mask)         fg[order_type::A] = base_mask;
+            if(fg[order_type::R] > fg[order_type::A]) fg[order_type::R] = fg[order_type::A];
+            if(fg[order_type::G] > fg[order_type::A]) fg[order_type::G] = fg[order_type::A];
+            if(fg[order_type::B] > fg[order_type::A]) fg[order_type::B] = fg[order_type::A];
 
             span->r = (value_type)fg[order_type::R];
             span->g = (value_type)fg[order_type::G];