Tools for GtkImageView

I have decided that I want to extend the GtkImageView widget to make it extensible. Right now, it handles showing images that you can zoom in on and drag around. It will be extended so that you can do the following things:

• Drag a selection on the widget. Very similar to how gThumbs Image->Crop dialog works.
• Various kinds of drawing operations.

I thought about implementing this as "tools":

+------------+
|            | 1     1 +-------------+
|GtkImageView| ------> |GtkIImageTool|
|            |         +-------------+
+------------+              |_____________________
                           /                      |
                 +-------------------+ +--------------------+
                 |GtkImageToolDragger| |GtkImageToolSelector|
                 +-------------------+ +--------------------+

In this diagram, GtkImageView has a reference to a GtkIImageTool which is an interface that abstracts out certain behaviour of GtkImageView. GtkImageToolDragger and GtkImageToolSelector are two concrete implementations of the GtkIImageTool interface. When GtkImageView references a GtkImageToolDragger, it behaves like normal. You have a hand cursor and can drag the image. When GtkImageView references a GtkImageToolSelector, it instead displays a selection cursor and you can make a rectangular selection on the image.

Using this arrangement, it is now possible to dynamically alter the behaviour of GtkImageView.

GtkImageView *view = GTK_IMAGE_VIEW (gtk_image_view_new ()); GtkImageToolSelector *selector = gtk_image_tool_selector_new (); gtk_image_view_set_tool (view, selector); /* The user can now make some selections on the image. We can query which area of the image that is selected. */ GdkRectangle rect; if (!gtk_image_tool_selector_get_selection (selector, &rect)) printf ("Nothing is selected!\n"); else printf ("You selected (%d, %d)-(%d, %d)\n", rect.x, rect.y, rect.width, rect.height);

It should be possible to achieve this, but the interface that GtkIImageTool will specify, might become to fat.

/* These are needed because the tool needs to be able to decide what happens when mouse events occur. */ gtk_iimage_tool_button_press () gtk_iimage_tool_button_release () gtk_iimage_tool_motion_notify () /* The tool needs to decide what the default cursor is. */ gtk_iimage_tool_get_default_cursor () /* The tool may need to do something when the pixbuf of the view is changed. */ gtk_iimage_tool_set_pixbuf () /* The tool will want to draw the image in a special way. */ gtk_iimage_tool_draw_pixbuf_data () /* The tool will want to tell GtkImageNav how the image data should be drawn as a thumbnail. */ gtk_iimage_tool_get_display_pixbuf ()