Re: what is an image

[Olexiy Avramchenko <olexiy ctech cn ua>]

Shiraz Baig wrote:
> I have tried to decipher the picture rendering in GTK,
> but I am not clear.  The ref documents are too brief
> and the tutorials do not cover this subject well.
>
> I have following questions.
>
> 1) We have a GtkImage and We have a GdkImage. What is
> the difference between the two?
GtkImage is a widget - it is used to display a picture on the screen 
within GTK+ framework, like GtkLabel is used to display some text.
GdkImage is a GDK object, it is used to locally hold a picture and do 
some manipulations with its content.

> 2) What is the difference between image, pixmap,
> pixbuf?
GdkImage and GdkPixbuf are stored locally (inside the memory of your 
process), while GdkPixmap lives in the XServer's memory (this can be 
somewhere on the network). So the main difference is that you can 
directly access the pixels of GtkImage and GdkPixbuf, but if you want to 
change anything in GdkPixmap you have to talk to XServer.

The difference of the GtkImage and GdkPixbuf is that GdkPixbuf uses 
small set of predefined formats to store the pixels (like RGB 8:8:8 
triplets or ARGB 8:8:8:8), while GtkImage holds raw pixels (format 
depends on your current hw configuration/video mode), ready to be send 
to video memory.
GdkPixbuf has some advantages over the GtkImage, like scaling support 
and loading picture from file.

> 3) What are the function calls involved starting from
> a picture stored in jpg file to rendering it on the
> screen.
Function to load GtkImage (the easy way to display a picture):
http://www.gtk.org/api/2.6/gtk/GtkImage.html#gtk-image-new-from-file

Function to load GdkPixbuf:
http://www.gtk.org/api/2.6/gdk-pixbuf/gdk-pixbuf-file-loading.html#gdk-pixbuf-new-from-file
One of the functions to render GdkPixbuf to some drawable:
http://www.gtk.org/api/2.6/gdk/gdk-Pixbufs.html#gdk-pixbuf-render-to-drawable

	Olexiy