Expose more png compression options

[tbonfort]

The wms shootout has shown that png compression options have a big influence on perceived performance, without necessarily causing larger image sizes.

One notable png optimization is to set png filtering to PNG_FILTER_NONE in these cases:

• quantized png
• when output is vector (i.e. no rasters) data

more testing should be done to assess the impact on raster images, but in any case png is not a good choice for this kind of data.

This ticket will track the addition of an additional FORMATOPTION allowing the user to set which png filters are applied. The default will be to not set any filter.

[tbonfort]

patch for mapimageio.c:

mapimageio.c

@@ -263 +263 @@
    if (!png_ptr)
       return (MS_FAILURE);
 
+   png_set_compression_level(png_ptr, compression);
+   png_set_filter(png_ptr,0,PNG_FILTER_NONE);
+
    info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
@@ -281 +284 @@
    else
       png_set_write_fn(png_ptr,info, png_write_data_to_buffer, png_flush_data);
    
-   png_set_compression_level(png_ptr, compression);
    
    if (rb->data.palette.num_entries <= 2)
     sample_depth = 1;
@@ -450 +452 @@
         if (!png_ptr)
             return (MS_FAILURE);
         
+        png_set_compression_level(png_ptr, compression);
+        png_set_filter(png_ptr,0,PNG_FILTER_NONE);
         info_ptr = png_create_info_struct(png_ptr);
         if (!info_ptr)
         {
@@ -473 +477 @@
         else
             color_type = PNG_COLOR_TYPE_RGB;
         
-        png_set_compression_level(png_ptr, compression);
         png_set_IHDR(png_ptr, info_ptr, rb->width, rb->height,
                      8, color_type, PNG_INTERLACE_NONE,
                      PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);

[tbonfort]

This modification should also be applied to MapCache

[tbonfort]

applied to mapcache in r12539

[tbonfort]

applied to mapserver in r12547