Re: Signals and callbacks

[Karl Mitchell <k l mitchell lancaster ac uk>]

I've recently begun programming in gtk and gdk-imlib, in an attempt to write
some fast stereo-imaging algorithms with a friendly GUI. For starters, I'm
working on an display program which shows two images of the same geographic
area in a paned window, the aim being to allow extraction of tie-points
between the images for input into the automatic stereo-matching routines.
However, I've been having one or two difficulties getting to grips with a
couple of fundamentals, and I was wondering whether anyone could help.

---
Firstly, images and pixels. At present I am displaying images as pixmap
widgets within event boxes. The online documentation suggests that the pixmap
widget should only be used for smaller images: is this a matter of style or is
there some advantage?

---
Secondly, signals and callbacks. I'm trying to implement a simple zoom routine
for each image, activated whenever the event box holding the image is clicked,
at present using:

    gtk_signal_connect (GTK_OBJECT (event_box_right), "button_press_event",
        GTK_SIGNAL_FUNC (magnify_image), NULL);

However, the magnify_image function needs quite a lot of information passed to
it:

    struct _imageData{
        GdkImlibImage *image;
        GtkWidget *pixmapwidget;
        gint magnification_factor;
    }

, and for the life of me I can't work out how to do it. I think it's something
to do with my lack of understanding of gpointers. Could anyone help me work
this one out?

Cheers,

-Karl

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