dwimage.txt

嵌入式浏览器Dillo源码

Jan 2001, [e-mail]
Updated May 2001

=======
DwImage
=======

A widget for displaying images and handling image maps.


Image Maps
==========

Client Side Image Maps
----------------------
You must first create a list of image maps: Allocate a DwImageMapList,
and initialize it by calling a_Dw_image_map_list_init. Adding a map is
done by a_Dw_image_map_list_add_map, a_Dw_image_map_list_add_shape
adds a shape to the last map. For the meaning of the link argument,
see Section "Signals".

Image maps are referred by a URL (not only by a name), but currently,
the image map list is stored in DilloHtmlLB, and there is no
possibility to parse documents without rendering, so images can only
use maps defined in the same document.

To use a map in an image, call a_Dw_image_set_usemap with the image,
the map list, and the URL of the map. Passing the whole list makes it
possible to use maps parsed after the image is created.


Server Side Image Maps
----------------------
To use images for server side image maps, you must call
a_Dw_image_set_ismap, and the style must contain a valid link
element. See section "Signals" for more details.


Signals
=======

There are four signals, which can be connected to process actions with
links. All have at least three arguments:

   - link is the link element of the DwStyle (server side image maps)
     or DwImageMapShape (client side image maps), respectively, an
     integer, which is currently only used for hypertext links, but
     generally, it depends on the signal callback how this value is
     used.

   - x and y are, when server side image maps are used, the relative
     coordinates of the mouse pointer, otherwise always -1.

Note that, unlike by DwPage before, no cursors are set, instead, the
signal callback function has to do this.

The signals:

   - void link_entered (DwPage *page,
                        gint link, gint x, gint y)

     Emitted when the link the mouse pointer is over has
     changed. "Changed" includes link, x and y, so this signal is also
     emitted each time the pointer is moved within a server side image
     map. If the pointer is outside of a link, all arguments have the
     value -1.


   - void link_pressed (DwPage *page,
                        gint link, gint x, gint y,
                        GdkEventButton *event)

     Emitted when the user presses a mouse button _inside_ a link,
     this signal is never emitted with link = -1. You can use the
     event to get information about the button, shift keys etc.


   - void link_released (DwPage *page,
                         gint link, gint x, gint y,
                         GdkEventButton *event)

   - void link_clicked (DwPage *page,
                        gint link, gint x, gint y,
                        GdkEventButton *event)

     Analogue to link_pressed.


Future Extentions
=================

  - Transparency could be done by clipping bitmaps, alpha (as
    provided by PNG) by dithered clipping bitmaps. This will increase
    the usage of X resources, but the current implementation (i)
    looks ugly on 8 bit displays, and (ii) will, as soon as
    background images are supported, make it necessary to rebuild the
    image at every call of Dw_image_size_allocate and so slow down
    rendering.

  - Animated GIF's are currently not supported.

  - Border for images used as link will be done with an extended
    DwStyle scheme.

  - There is little code for support of background images in
    a_dw_gtk_viewport.c (only internal code, no interfaces yet, and it
    will probably move into DwStyle), but this code needs a GdkPixmap,
    or at least an RGB buffer. The the code of the Image module should
    be used for this somehow.