Re: How to store Gdk::Pixbuf pixels into std::string objects

[Glus Xof <gtglus gmail com>]

2015-02-23 22:21 GMT+01:00 Markus Kolb <markus kolb+gtkmm tower-net de>:

Am 2015-02-23 21:40, schrieb Glus Xof:

Hi guys,

Before anything, I admit that probably my question is not an specifically
Gtkmm question... but nevertheless I think you may know how Gdk::Pixbuf is
done...

Having the following,

Glib::RefPtr<Gdk::Pixbuf> ref_orig = Gdk::Pixbuf::create_from_file
("./file.png");

I'm trying to temporary store (because I need so) the image data into a
std::string object. It seems that get_pixels() could solve the problem,
getting a pointer of type guint8.

Seems that gdkmm is not up-to-date here.
gdk uses a guchar*. But this shouldn't be a problem.

 

So, I wrote as follows,

std::string image_pixels (reinterpret_cast<const char
*>(ref_orig->get_pixels()), ref_orig->get_rowstride());

I think this does not what you expect.

https://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-The-GdkPixbuf-Structure.html#gdk-pixbuf-get-rowstride

See also the part below the description headline.

Maybe you should use gsize Gdk::Pixbuf::get_byte_length()
because https://developer.gnome.org/gdk-pixbuf/stable/gdk-pixbuf-The-GdkPixbuf-Structure.html#gdk-pixbuf-get-pixels-with-length is missing.

I hope it will help you.

But think about the std::string. Big ? ;-)

According to Yann & Markus' comments, I remake my code as follows,

Glib::RefPtr<Gdk::Pixbuf> ref_orig = Gdk::Pixbuf::create_from_file ("./file.png");

// Glib::ustring::c_str() or data() allows me to get an std::string object...

Glib::ustring image_pixels (
      reinterpret_cast<const char *>(ref_orig->get_pixels()),
      ref_orig->get_byte_length());

Glib::RefPtr<Gdk::Pixbuf> ref_dest =
      Gdk::Pixbuf::create_from_data (
         reinterpret_cast<const guint8*>(image_pixels.data()), Gdk::COLORSPACE_RGB,
         ref_orig->get_has_alpha(), ref_orig->get_bits_per_sample(),
         ref_orig->get_width(), ref_orig->get_height(), ref_orig->get_rowstride());

But, at runtime I get a lenght error exception,

terminate called after throwing an instance of 'std::length_error'
  what():  basic_string::_S_create

Could help ?

Glus

 

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