[libpng16] Added PNG_IMAGE_FLAG_FAST for the benefit of applications that

store intermediate files, or intermediate in-memory data, while processing
image data with the simplified API.  The option makes the files larger
but faster to write and read.  pngstest now uses this by default; this
can be disabled with the --slow option.

pngwrite.c

@@ -731,6 +731,15 @@ png_write_row(png_structrp png_ptr, png_const_bytep row)
    }
 #endif
 
+#if 0 /* To do: implement png_do_check_palette_indexes() */
+   /* Check for out-of-range palette index */
+   if (png_ptr->num_palette < (1 << png_ptr->bit_depth))
+      png_do_check_palette_indexes(&row_info, png_ptr->row_buf + 1,
+        png_ptr->num_palette_max);
+   if (png_ptr->num_palette_max > num_palette + 1)
+      png_warning(png_ptr, "Palette index exceeded num_palette");
+#endif
+
    /* Find a filter if necessary, filter the row and write it out. */
    png_write_find_filter(png_ptr, &row_info);
 
@@ -2109,6 +2118,18 @@ png_image_write_main(png_voidp argument)
       display->row_bytes = row_bytes;
    }
 
+   /* Apply 'fast' options if the flag is set. */
+   if ((image->flags & PNG_IMAGE_FLAG_FAST) != 0)
+   {
+      png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_NO_FILTERS);
+      /* NOTE: determined by experiment using pngstest, this reflects some
+       * balance between the time to write the image once and the time to read
+       * it about 50 times.  The speed-up in pngstest was about 10-20% of the
+       * total (user) time on a heavily loaded system.
+       */
+      png_set_compression_level(png_ptr, 3);
+   }
+
    /* Check for the cases that currently require a pre-transform on the row
     * before it is written.  This only applies when the input is 16-bit and
     * either there is an alpha channel or it is converted to 8-bit.