on Win32, --enable-gdiplus makes pixbuf loading 6 times slower

[Adam Dingle <adam yorba org>]

We're developing a photo management application which uses GTK on Win32 
using the prebuilt GTK binaries available at 
http://ftp.gnome.org/pub/GNOME/binaries/win32/gtk+/ .  We noticed that 
pixbuf loading (via gdk_pixbuf_new_from_file) slowed down massively (by 
a factor of >6) in the transition from GTK 2.18.1 to GTK 2.18.3, and has 
remained slow ever since.  This has made the newer binary releases 
unusable for us.

It appears that starting with GTK 2.18.3, Windows binaries have been 
configured using --enable-gdiplus to enable the GDI+ pixbuf loader (see 
http://aruiz.synaptia.net/siliconisland/2009/08/dear-lazyweb-gtk-need-gdi-help.html), 
even though --enable-gdiplus is apparently still off by default in 
configure.in.  I believe that Tor Lindquist builds the Windows GTK 
binaries.  Tor, can you confirm that you turned on --enable-gdiplus 
starting with GTK 2.18.3?  I think we should probably build without GDI+ 
until/unless its pixbuf loading can be made faster.

Here's a test program in C which you can use to see how long pixbufs 
take to load.

// load.c
// to build: gcc -Wall load.c `pkg-config --cflags --libs gtk+-2.0` -o load
#include <stdio.h>
#include <gdk-pixbuf/gdk-pixbuf.h>
#include <gtk/gtk.h>

int main(int argc, char *argv[]) {
   gtk_init(&argc, &argv);
  
   int i;
   for (i = 1 ; i < argc ; ++i) {
       GError *error = NULL;
       GdkPixbuf *p = gdk_pixbuf_new_from_file(argv[i], &error);
       printf(p ? "imported %s\n" : "import error: %s\n", argv[i]);
   }
   return 0;
}
// end

-adam