>From the IUP official docs: "But the available file formats supported are system dependent. The Windows driver supports BMP, ICO and CUR. The GTK driver supports the formats supported by the GDK-PixBuf library, such as BMP, GIF, JPEG, PCX, PNG, TIFF and many others. The Motif driver supports the X-Windows bitmap."
May be there is some problem with GDK-PixBuf library. I would use BMP format , it worked fine with buttons.
