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GNOME Canvas Library Reference Manual | |
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| Top | Description | Object Hierarchy | Properties | Signals | ||||
#include <libgnomecanvas/libgnomecanvas.h>
GnomeCanvasItem;
GnomeCanvasItemClass;
GnomeCanvasItem * gnome_canvas_item_new (GnomeCanvasGroup *parent,
GType type,
const gchar *first_arg_name,
...);
void gnome_canvas_item_construct (GnomeCanvasItem *item,
GnomeCanvasGroup *parent,
const gchar *first_arg_name,
va_list args);
void gnome_canvas_item_set (GnomeCanvasItem *item,
const gchar *first_arg_name,
...);
void gnome_canvas_item_set_valist (GnomeCanvasItem *item,
const gchar *first_arg_name,
va_list args);
void gnome_canvas_item_move (GnomeCanvasItem *item,
double dx,
double dy);
void gnome_canvas_item_affine_relative (GnomeCanvasItem *item,
const double affine[6]);
void gnome_canvas_item_affine_absolute (GnomeCanvasItem *item,
const double affine[6]);
void gnome_canvas_item_raise (GnomeCanvasItem *item,
int positions);
void gnome_canvas_item_lower (GnomeCanvasItem *item,
int positions);
void gnome_canvas_item_raise_to_top (GnomeCanvasItem *item);
void gnome_canvas_item_lower_to_bottom (GnomeCanvasItem *item);
void gnome_canvas_item_show (GnomeCanvasItem *item);
void gnome_canvas_item_hide (GnomeCanvasItem *item);
int gnome_canvas_item_grab (GnomeCanvasItem *item,
unsigned int event_mask,
GdkCursor *cursor,
guint32 etime);
void gnome_canvas_item_ungrab (GnomeCanvasItem *item,
guint32 etime);
void gnome_canvas_item_w2i (GnomeCanvasItem *item,
double *x,
double *y);
void gnome_canvas_item_i2w (GnomeCanvasItem *item,
double *x,
double *y);
void gnome_canvas_item_i2w_affine (GnomeCanvasItem *item,
double affine[6]);
void gnome_canvas_item_i2c_affine (GnomeCanvasItem *item,
double affine[6]);
void gnome_canvas_item_reparent (GnomeCanvasItem *item,
GnomeCanvasGroup *new_group);
void gnome_canvas_item_grab_focus (GnomeCanvasItem *item);
void gnome_canvas_item_get_bounds (GnomeCanvasItem *item,
double *x1,
double *y1,
double *x2,
double *y2);
void gnome_canvas_item_request_update (GnomeCanvasItem *item);
GObject
+----GInitiallyUnowned
+----GtkObject
+----GnomeCanvasItem
+----GnomeCanvasShape
+----GnomeCanvasGroup
+----GnomeCanvasLine
+----GnomeCanvasPixbuf
+----GnomeCanvasRichText
+----GnomeCanvasText
+----GnomeCanvasWidget
This is the base class for all canvas items. Canvas items are the drawing elements of a GnomeCanvas. Example items include lines, ellipses, polygons, images, text, curves and even arbitrary GTK+ widgets.
Canvas items use the GObject property system to query and set parameters. Properties are inherited so, for example, a GnomeCanvasPolygon has a "fill-color" property that is inherited from its parent class object GnomeCanvasShape. So be sure to check the parent classes of GnomeCanvasItem objects when looking for item properties. More information on GObject properties can be found in the glib library GObject API reference documentation.
To create a new canvas item call gnome_canvas_item_new() which takes a
parent GnomeCanvasGroup, GType of the item to create, and a NULL terminated
list of name/value GObject properties to set for the new item.
To change an existing canvas item's properties call gnome_canvas_item_set(),
or g_object_set() can also be used.
There are several functions to change the drawing stacking order of an item.
Call gnome_canvas_item_raise() to raise an item a specified number of
positions or gnome_canvas_item_lower() to lower it. To raise an item to the
top call gnome_canvas_item_raise_to_top(). The
gnome_canvas_item_lower_to_bottom() function will put it at the bottom.
To show an item call gnome_canvas_item_show(). Note that canvas item's are
shown by default and so do not need to be explicitly shown after creation
(contrary to GTK+ widget behavior). Call gnome_canvas_item_hide() to hide an
item.
To move an item relative to its current position (item coordinates) call
gnome_canvas_item_move() or gnome_canvas_item_affine_relative() for more
complex transforms. gnome_canvas_item_affine_absolute() can be used to
set an item's transform to specific values (not offsets).
To convert between world and item coordinate systems call
gnome_canvas_item_w2i(), and to convert in the other direction call
gnome_canvas_item_i2w(). To get the transform for converting from item
to world coordinates use gnome_canvas_item_i2w_affine() or for converting
item to canvas coordinates, gnome_canvas_item_i2c_affine().
Handling user input for interactive items is accomplished through a
few functions and the "event" signal. To grab the mouse cursor call
gnome_canvas_item_grab(), it can be ungrabbed with
gnome_canvas_item_ungrab() (see gdk_pointer_grab() of the GTK+ library
for details). To grab keyboard focus call
gnome_canvas_item_grab_focus(). Received events will be signaled via
the "event" signal.
Some other useful functions include a reparenting routine,
gnome_canvas_item_reparent(), and a function to query the bounding
box of an item (a minumum rectangular area containing all parts of the item),
gnome_canvas_item_get_bounds().
typedef struct _GnomeCanvasItem GnomeCanvasItem;
This structure should not be accessed directly. Use the object's properties and functions for querying or changing its parameters.
typedef struct {
GtkObjectClass parent_class;
/* Tell the item to update itself. The flags are from the update flags
* defined above. The item should update its internal state from its
* queued state, and recompute and request its repaint area. The
* affine, if used, is a pointer to a 6-element array of doubles. The
* update method also recomputes the bounding box of the item.
*/
void (* update) (GnomeCanvasItem *item, double *affine, ArtSVP *clip_path, int flags);
/* Realize an item -- create GCs, etc. */
void (* realize) (GnomeCanvasItem *item);
/* Unrealize an item */
void (* unrealize) (GnomeCanvasItem *item);
/* Map an item - normally only need by items with their own GdkWindows */
void (* map) (GnomeCanvasItem *item);
/* Unmap an item */
void (* unmap) (GnomeCanvasItem *item);
/* Return the microtile coverage of the item */
ArtUta *(* coverage) (GnomeCanvasItem *item);
/* Draw an item of this type. (x, y) are the upper-left canvas pixel
* coordinates of the drawable, a temporary pixmap, where things get
* drawn. (width, height) are the dimensions of the drawable.
*/
void (* draw) (GnomeCanvasItem *item, GdkDrawable *drawable,
int x, int y, int width, int height);
/* Render the item over the buffer given. The buf data structure
* contains both a pointer to a packed 24-bit RGB array, and the
* coordinates. This method is only used for antialiased canvases.
*
* TODO: figure out where clip paths fit into the rendering framework.
*/
void (* render) (GnomeCanvasItem *item, GnomeCanvasBuf *buf);
/* Calculate the distance from an item to the specified point. It also
* returns a canvas item which is the item itself in the case of the
* object being an actual leaf item, or a child in case of the object
* being a canvas group. (cx, cy) are the canvas pixel coordinates that
* correspond to the item-relative coordinates (x, y).
*/
double (* point) (GnomeCanvasItem *item, double x, double y, int cx, int cy,
GnomeCanvasItem **actual_item);
/* Fetch the item's bounding box (need not be exactly tight). This
* should be in item-relative coordinates.
*/
void (* bounds) (GnomeCanvasItem *item, double *x1, double *y1, double *x2, double *y2);
/* Signal: an event occurred for an item of this type. The (x, y)
* coordinates are in the canvas world coordinate system.
*/
gboolean (* event) (GnomeCanvasItem *item, GdkEvent *event);
/* Reserved for future expansion */
gpointer spare_vmethods [4];
} GnomeCanvasItemClass;
The internals of this class structure are of interest to those creating objects derived from GnomeCanvasItem.
| Parent derived class. | |
| Update method called to tell the item to update itself. | |
| Realize an item (create graphics contexts, etc). | |
| Unrealize an item. | |
| Map an item - normally only needed by items with their own GdkWindows. | |
| Unmap an item. | |
| Return the microtile coverage of the item. | |
| Draw an item of this type. | |
| Render the item for anti-aliased canvases. | |
| Calculate the distance from an item to a point. | |
| Fetch the item's bounding box (rectangular area it occupies). | |
| The class signal method for the "event" signal. | |
| Reserved. |
GnomeCanvasItem * gnome_canvas_item_new (GnomeCanvasGroup *parent, GType type, const gchar *first_arg_name, ...);
Creates a new canvas item with parent as its parent group. The item is
created at the top of its parent's stack, and starts up as visible. The item
is of the specified type, for example, it can be
gnome_canvas_rect_get_type(). The list of object arguments/value pairs is
used to configure the item. If you need to pass construct time parameters, you
should use g_object_new() to pass the parameters and
gnome_canvas_item_construct() to set up the canvas item.
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The parent group for the new item. |
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The object type of the item. |
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A list of object argument name/value pairs, NULL-terminated, used to configure the item. For example, "fill_color", "black", "width_units", 5.0, NULL. |
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Returns : |
The newly-created item. |
void gnome_canvas_item_construct (GnomeCanvasItem *item, GnomeCanvasGroup *parent, const gchar *first_arg_name, va_list args);
Constructs a canvas item; meant for use only by item implementations.
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An unconstructed canvas item. |
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The parent group for the item. |
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The name of the first argument for configuring the item. |
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The list of arguments used to configure the item. |
void gnome_canvas_item_set (GnomeCanvasItem *item, const gchar *first_arg_name, ...);
Configures a canvas item. The arguments in the item are set to the specified values, and the item is repainted as appropriate.
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A canvas item. |
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The list of object argument name/value pairs used to configure the item. |
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void gnome_canvas_item_set_valist (GnomeCanvasItem *item, const gchar *first_arg_name, va_list args);
Configures a canvas item. The arguments in the item are set to the specified values, and the item is repainted as appropriate.
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A canvas item. |
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The name of the first argument used to configure the item. |
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The list of object argument name/value pairs used to configure the item. |
void gnome_canvas_item_move (GnomeCanvasItem *item, double dx, double dy);
Moves a canvas item by creating an affine transformation matrix for translation by using the specified values. This happens in item local coordinate system, so if you have nontrivial transform, it most probably does not do, what you want.
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A canvas item. |
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Horizontal offset. |
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Vertical offset. |
void gnome_canvas_item_affine_relative (GnomeCanvasItem *item, const double affine[6]);
Combines the specified affine transformation matrix with the item's current transformation. NULL affine is not allowed.
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A canvas item. |
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An affine transformation matrix. |
void gnome_canvas_item_affine_absolute (GnomeCanvasItem *item, const double affine[6]);
Makes the item's affine transformation matrix be equal to the specified matrix. NULL affine is treated as identity.
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A canvas item. |
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An affine transformation matrix. |
void gnome_canvas_item_raise (GnomeCanvasItem *item, int positions);
Raises the item in its parent's stack by the specified number of positions. If the number of positions is greater than the distance to the top of the stack, then the item is put at the top.
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A canvas item. |
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Number of steps to raise the item. |
void gnome_canvas_item_lower (GnomeCanvasItem *item, int positions);
Lowers the item in its parent's stack by the specified number of positions. If the number of positions is greater than the distance to the bottom of the stack, then the item is put at the bottom.
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A canvas item. |
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Number of steps to lower the item. |
void gnome_canvas_item_raise_to_top (GnomeCanvasItem *item);
Raises an item to the top of its parent's stack.
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A canvas item. |
void gnome_canvas_item_lower_to_bottom (GnomeCanvasItem *item);
Lowers an item to the bottom of its parent's stack.
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A canvas item. |
void gnome_canvas_item_show (GnomeCanvasItem *item);
Shows a canvas item. If the item was already shown, then no action is taken.
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A canvas item. |
void gnome_canvas_item_hide (GnomeCanvasItem *item);
Hides a canvas item. If the item was already hidden, then no action is taken.
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A canvas item. |
int gnome_canvas_item_grab (GnomeCanvasItem *item, unsigned int event_mask, GdkCursor *cursor, guint32 etime);
Specifies that all events that match the specified event mask should be sent
to the specified item, and also grabs the mouse by calling
gdk_pointer_grab(). The event mask is also used when grabbing the pointer.
If cursor is not NULL, then that cursor is used while the grab is active.
The etime parameter is the timestamp required for grabbing the mouse.
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A canvas item. |
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Mask of events that will be sent to this item. |
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If non-NULL, the cursor that will be used while the grab is active. |
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The timestamp required for grabbing the mouse, or GDK_CURRENT_TIME. |
Returns : |
If an item was already grabbed, it returns GDK_GRAB_ALREADY_GRABBED. If
the specified item was hidden by calling gnome_canvas_item_hide(), then it
returns GDK_GRAB_NOT_VIEWABLE. Else, it returns the result of calling
gdk_pointer_grab().
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void gnome_canvas_item_ungrab (GnomeCanvasItem *item, guint32 etime);
Ungrabs the item, which must have been grabbed in the canvas, and ungrabs the mouse.
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A canvas item that holds a grab. |
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The timestamp for ungrabbing the mouse. |
void gnome_canvas_item_w2i (GnomeCanvasItem *item, double *x, double *y);
Converts a coordinate pair from world coordinates to item-relative coordinates.
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A canvas item. |
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X coordinate to convert (input/output value). |
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Y coordinate to convert (input/output value). |
void gnome_canvas_item_i2w (GnomeCanvasItem *item, double *x, double *y);
Converts a coordinate pair from item-relative coordinates to world coordinates.
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A canvas item. |
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X coordinate to convert (input/output value). |
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Y coordinate to convert (input/output value). |
void gnome_canvas_item_i2w_affine (GnomeCanvasItem *item, double affine[6]);
Gets the affine transform that converts from the item's coordinate system to world coordinates.
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A canvas item |
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An affine transformation matrix (return value). |
void gnome_canvas_item_i2c_affine (GnomeCanvasItem *item, double affine[6]);
Gets the affine transform that converts from item-relative coordinates to canvas pixel coordinates.
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A canvas item. |
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An affine transformation matrix (return value). |
void gnome_canvas_item_reparent (GnomeCanvasItem *item, GnomeCanvasGroup *new_group);
Changes the parent of the specified item to be the new group. The item keeps its group-relative coordinates as for its old parent, so the item may change its absolute position within the canvas.
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A canvas item. |
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A canvas group. |
void gnome_canvas_item_grab_focus (GnomeCanvasItem *item);
Makes the specified item take the keyboard focus, so all keyboard events will be sent to it. If the canvas widget itself did not have the focus, it grabs it as well.
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A canvas item. |
void gnome_canvas_item_get_bounds (GnomeCanvasItem *item, double *x1, double *y1, double *x2, double *y2);
Queries the bounding box of a canvas item. The bounds are returned in the coordinate system of the item's parent.
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A canvas item. |
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Leftmost edge of the bounding box (return value). |
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Upper edge of the bounding box (return value). |
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Rightmost edge of the bounding box (return value). |
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Lower edge of the bounding box (return value). |
void gnome_canvas_item_request_update (GnomeCanvasItem *item);
To be used only by item implementations. Requests that the canvas queue an update for the specified item.
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A canvas item. |
"parent" property"parent" GnomeCanvasItem* : Read / Write
Parent GnomeCanvasGroup that contains the item.
"event" signalgboolean user_function (GnomeCanvasItem *canvasitem, GdkEvent *event, gpointer user_data) : Run Last
Signals mouse button clicks, motion, enter/leave, and key press events
on canvas items. Use this signal to create user interactive items.
The x and y
coordinates of the event structure have been converted to canvas world
coordinates.
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the object which received the signal. |
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A GdkEvent structure containing the event that occurred. |
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user data set when the signal handler was connected. |
Returns : |
Signal handlers should return TRUE to stop signal emission or FALSE
to allow other signal handlers to process this event.
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