[libpng16] Fixed NO_WRITE_FILTER and -Wconversion build breaks (John Bowler).

ANNOUNCE

@@ -73,11 +73,13 @@ Version 1.6.18beta07 [June 3, 2015]
   Removed non-working progressive reader 'skip' function. This
     function has apparently never been used. It was implemented
     to support back-door modification of png_struct in libpng-1.4.x
-    but was apparently never tested (because it does nothing and cannot
-    do anything).
+    but (because it does nothing and cannot do anything) was apparently
+    never tested (John Bowler).
   Fixed cexcept.h in which GCC 5 now reports that one of the auto
     variables in the Try macro needs to be volatile to prevent value
-    being lost over the setjmp.
+    being lost over the setjmp (John Bowler).
+  Fixed NO_WRITE_FILTER and -Wconversion build breaks (John Bowler).
+
 
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CHANGES

@@ -5258,11 +5258,12 @@ Version 1.6.18beta07 [June 3, 2015]
   Removed non-working progressive reader 'skip' function. This
     function has apparently never been used. It was implemented
     to support back-door modification of png_struct in libpng-1.4.x
-    but was apparently never tested (because it does nothing and cannot
-    do anything).
+    but (because it does nothing and cannot do anything) was apparently
+    never tested (John Bowler).
   Fixed cexcept.h in which GCC 5 now reports that one of the auto
     variables in the Try macro needs to be volatile to prevent value
-    being lost over the setjmp.
+    being lost over the setjmp (John Bowler).
+  Fixed NO_WRITE_FILTER and -Wconversion build breaks (John Bowler).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

pngwrite.c

@@ -1032,6 +1032,7 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
 #endif /* WRITE_FILTER */
       }
 
+#ifdef PNG_WRITE_FILTER_SUPPORTED
       /* If we have allocated the row_buf, this means we have already started
        * with the image and we should have allocated all of the filter buffers
        * that have been selected.  If prev_row isn't already allocated, then
@@ -1101,20 +1102,14 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
          }
       }
       png_ptr->do_filter = (png_byte)filters;
+#endif
    }
    else
       png_error(png_ptr, "Unknown custom filter method");
 }
 
-/* This allows us to influence the way in which libpng chooses the "best"
- * filter for the current scanline.  While the "minimum-sum-of-absolute-
- * differences metric is relatively fast and effective, there is some
- * question as to whether it can be improved upon by trying to keep the
- * filtered data going to zlib more consistent, hopefully resulting in
- * better compression.
- */
-#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED      /* GRR 970116 */
-/* Provide floating and fixed point APIs (DEPRECATED) */
+#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* DEPRECATED */
+/* Provide floating and fixed point APIs */
 #ifdef PNG_FLOATING_POINT_SUPPORTED
 void PNGAPI
 png_set_filter_heuristics(png_structrp png_ptr, int heuristic_method,

pngwutil.c

@@ -1962,7 +1962,7 @@ png_write_start_row(png_structrp png_ptr)
    int usr_pixel_depth;
 
 #ifdef PNG_WRITE_FILTER_SUPPORTED
-   int filters;
+   png_byte filters;
 #endif
 
    png_debug(1, "in png_write_start_row");
@@ -1983,10 +1983,10 @@ png_write_start_row(png_structrp png_ptr)
    filters = png_ptr->do_filter;
 
    if (png_ptr->height == 1)
-      filters &= ~(PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH);
+      filters &= 0xff & ~(PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH);
 
    if (png_ptr->width == 1)
-      filters &= ~(PNG_FILTER_SUB|PNG_FILTER_AVG|PNG_FILTER_PAETH);
+      filters &= 0xff & ~(PNG_FILTER_SUB|PNG_FILTER_AVG|PNG_FILTER_PAETH);
 
    if (filters == 0)
       filters = PNG_FILTER_NONE;