The gdk-pixbuf Library | |||
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"pixbuf" |
This canvas item displays
In addition to the normal affine transformations supported by canvas items, the GnomeCanvasPixbuf item supports independent object arguments for scaling and translation. This is useful for explicitly setting a size to which the pixbuf's image will be scaled, and for specifying translation offsets that take place in the item's local coordinate system.
By default, the pixbuf canvas item will attain the size in units
of the
To set custom width and height values, you must set the width_set or height_set
arguments to TRUE, and then set the width or height arguments to
the desired values. The former two arguments control whether
the latter two are used when computing the final image's size;
they are both FALSE by default so that the pixbuf item will
attain a size in units equal to the size in pixels of the
The custom translation offsets are controlled by the x and y arguments. The logical upper-left vertex of the image will be translated by the specified distance, aligned with the item's local coordinate system.
The Scalable Vector Graphics specification (SVG) of the World Wide Web Consortium also allows images to be translated and scaled by absolute pixel values that are independent of an item's normal affine transformation.
Normally, the pixbuf item's translation and scaling arguments are interpreted in units, so they will be modified by the item's affine transformation. The width_in_pixels, height_in_pixels, x_in_pixels, and y_in_pixels object arguments can be used to modify this behavior. If one of these arguments is TRUE, then the corresponding scaling or translation value will not be affected lengthwise by the pixbuf item's affine transformation.
For example, consider a pixbuf item whose size is (300, 200). If the item is modified with a scaling transformation of (0.5, 2.0) but the width_in_pixels is set to TRUE, then the item will appear to be (300, 400) pixels in size. This means that in this case the item's affine transformation only applies to the height value, while the width value is kept in absolute pixels.
Likewise, consider a pixbuf item whose (x, y) arguments are set to (30, 40). If the item is then modified by the same scaling transformation of (0.5, 2.0) but the y_in_pixels argument is set to TRUE, then the image's upper-left corner will appear to be at position (15, 40). In this case, the affine transformation is applied only to the x offset, while the y offset is kept in absolute pixels.
In short, these arguments control whether a particular dimension of a pixbuf item is scaled or not in the normal way by the item's affine transformation.
When you set the
This means that if an application just needs to load a pixbuf image and set it into a pixbuf canvas item, it can do the following to ‘forget’ about the pixbuf structure:
GdkPixbuf *pixbuf; GnomeCanvasItem *item; pixbuf = gdk_pixbuf_new_from_file ("foo.png"); g_assert (pixbuf != NULL); item = gnome_canvas_item_new (gnome_canvas_root (my_canvas), |
After this happens, the reference count of the pixbuf structure will be 1: the gdk_pixbuf_new_from_file() function creates it with a reference count of 1, then setting the pixbuf argument of the GnomeCanvasPixbuf item increases it to 2, and then it is decremented to 1 by the call to gdk_pixbuf_unref(). When the canvas item is destroyed, it will automatically unreference the pixbuf structure again, causing its reference count to drop to zero and thus be freed.
#define GNOME_CANVAS_PIXBUF(obj) |
Casts a
obj : | A GTK+ object. |
Contains a pointer to a
Indicates the width the pixbuf will be scaled to. This argument will only be used if the width_set argument is TRUE. If the width_in_pixels argument is FALSE, the width will be taken to be in canvas units, and thus will be scaled along with the canvas item's affine transformation. If width_in_pixels is TRUE, the width will be taken to be in pixels, and will visually remain a constant size even if the item's affine transformation changes.
Determines whether the width argument is taken into account when scaling the pixbuf item. If this argument is FALSE, then the width value of the pixbuf will be used instead. This argument is FALSE by default.
If this argument is TRUE, then the width of the pixbuf will be considered to be in pixels, that is, it will not be visually scaled even if the item's affine transformation changes. If this is FALSE, then the width of the pixbuf will be considered to be in canvas units, and so will be scaled normally by affine transformations. The default is FALSE.
Indicates the height the pixbuf will be scaled to. This argument will only be used if the height_set argument is TRUE. Works in the same way as the width argument.
Determines whether the height argument is taken into account when scaling the pixbuf item. Works in the same way as the width_set argument. The default is FALSE.
Works in the same way as the width_in_pixels argument. The default is FALSE.
Indicates the horizontal translation offset of the pixbuf item's image. This offset may not actually appear horizontal, since it will be affected by the item's affine transformation. The default is 0.0.
If this argument is TRUE, the pixbuf's translation with respect to its logical origin in item-relative coordinates will be in pixels, that is, the visible offset will not change even if the item's affine transformation changes. If it is FALSE, the pixbuf's translation will be taken to be in canvas units, and thus will change along with the item's affine transformation. The default is FALSE.
Indicates the vertical translation offset of the pixbuf item's image. Works in the same way as the x argument. The default is 0.0.
Works in the same way as the x_in_pixels argument, but controls whether the y translation offset is scaled or not. The default is FALSE.