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GdkPaintable is a simple interface used by GDK and GDK to represent objects that can be painted anywhere at any size without requiring any sort of layout. The interface is inspired by similar concepts elsewhere, such as ClutterContent, HTML/CSS Paint Sources, or SVG Paint Servers.
A GdkPaintable can be snapshot at any time and size using
gdk_paintable_snapshot()
. How the paintable interprets that size and if it
scales or centers itself into the given rectangle is implementation defined,
though if you are implementing a GdkPaintable and don't know what to do, it
is suggested that you scale your paintable ignoring any potential aspect ratio.
The contents that a GdkPaintable produces may depend on the GdkSnapshot passed to it. For example, paintables may decide to use more detailed images on higher resolution screens or when OpenGL is available. A GdkPaintable will however always produce the same output for the same snapshot.
A GdkPaintable may change its contents, meaning that it will now produce a
different output with the same snpashot. Once that happens, it will call
gdk_paintable_invalidate_contents()
which will emit the
“invalidate-contents” signal.
If a paintable is known to never change its contents, it will set the
GDK_PAINTABLE_STATIC_CONTENT
flag. If a consumer cannot deal with changing
contents, it may call gdk_paintable_get_static_image()
which will return a
static paintable and use that.
A paintable can report an intrinsic (or preferred) size or aspect ratio it
wishes to be rendered at, though it doesn't have to. Consumers of the interface
can use this information to layout thepaintable appropriately.
Just like the contents, the size of a paintable can change. A paintable will
indicate this by calling gdk_paintable_invalidate_size()
which will emit the
“invalidate-size” signal.
And just like for contents, if a paintable is known to never change its size,
it will set the GDK_PAINTABLE_STATIC_SIZE
flag.
Besides API for applications, there are some functions that are only
useful for implementing subclasses and should not be used by applications:
gdk_paintable_invalidate_contents()
,
gdk_paintable_invalidate_size()
,
gdk_paintable_new_empty()
.
GdkPaintable *
gdk_paintable_get_current_image (GdkPaintable *paintable
);
Gets an immutable paintable for the current contents displayed by paintable
.
This is useful when you want to retain the current state of an animation, for example to take a screenshot of a running animation.
If the paintable
is already immutable, it will return itself.
void gdk_paintable_snapshot (GdkPaintable *paintable
,GdkSnapshot *snapshot
,double width
,double height
);
Snapshots the given paintable with the given width
and height
at the
current (0,0) offset of the snapshot
. If width
and height
are not larger
than zero, this function will do nothing.
paintable |
||
snapshot |
a GdkSnapshot to snapshot to |
|
width |
width to snapshot in |
|
height |
height to snapshot in |
GdkPaintableFlags
gdk_paintable_get_flags (GdkPaintable *paintable
);
Get flags for the paintable. This is oftentimes useful for optimizations.
See GdkPaintableFlags for the flags and what they mean.
int
gdk_paintable_get_intrinsic_width (GdkPaintable *paintable
);
Gets the preferred width the paintable
would like to be displayed at.
Consumers of this interface can use this to reserve enough space to draw
the paintable.
This is a purely informational value and does not in any way limit the values
that may be passed to gdk_paintable_snapshot()
.
If the paintable
does not have a preferred width, it returns 0. Negative
values are never returned.
int
gdk_paintable_get_intrinsic_height (GdkPaintable *paintable
);
Gets the preferred height the paintable
would like to be displayed at.
Consumers of this interface can use this to reserve enough space to draw
the paintable.
This is a purely informational value and does not in any way limit the values
that may be passed to gdk_paintable_snapshot()
.
If the paintable
does not have a preferred height, it returns 0. Negative
values are never returned.
double
gdk_paintable_get_intrinsic_aspect_ratio
(GdkPaintable *paintable
);
Gets the preferred aspect ratio the paintable
would like to be displayed at.
The aspect ration is the width divided by the height, so a value of 0.5 means
that the paintable
prefers to be displayed twice as high as it is wide.
Consumers of this interface can use this to preserve aspect ratio when displaying
this paintable.
This is a purely informational value and does not in any way limit the values
that may be passed to gdk_paintable_snapshot()
.
Usually when a paintable
returns non-0 values from
gdk_paintable_get_intrinsic_width()
and gdk_paintable_get_intrinsic_height()
the aspect ratio should conform to those values, though that is not required.
If the paintable
does not have a preferred aspect ratio, it returns 0.0.
Negative values are never returned.
void gdk_paintable_compute_concrete_size (GdkPaintable *paintable
,double specified_width
,double specified_height
,double default_width
,double default_height
,double *concrete_width
,double *concrete_height
);
Applies the sizing algorithm outlined in
https://drafts.csswg.org/css-images-3/default-sizing
to the given paintable
. See that link for more details.
It is not necessary to call this function when both specified_width
and specified_height
are known, but it is useful to call this
function in GtkWidget:measure implementations to compute the
other dimension when only one dimension is given.
paintable |
||
specified_width |
the width |
|
specified_height |
the height |
|
default_width |
the width |
|
default_height |
the height |
|
concrete_width |
will be set to the concrete width computed. |
[out] |
concrete_height |
will be set to the concrete height computed. |
[out] |
void
gdk_paintable_invalidate_contents (GdkPaintable *paintable
);
Called by implementations of GdkPaintable to invalidate their contents. Unless the contents are invalidated, implementations must guarantee that multiple calls to GdkPaintable::snapshot produce the same output.
This function will emit the GdkPaintable::invalidate-contents signal.
If a paintable
reports the GDK_PAINTABLE_STATIC_CONTENTS
flag,
it must not call this function.
void
gdk_paintable_invalidate_size (GdkPaintable *paintable
);
Called by implementations of GdkPaintable to invalidate their size.
As long as the size is not invalidated, paintable
must return the same values
for its width, height and intrinsic height.
This function will emit the GdkPaintable::invalidate-size signal.
If a paintable
reports the GDK_PAINTABLE_STATIC_SIZE
flag,
it must not call this function.
GdkPaintable * gdk_paintable_new_empty (int intrinsic_width
,int intrinsic_height
);
Returns a paintable that has the given intrinsic size and draws nothing.
This is often useful for implementing the GdkPaintableClass:get_current_image()
virtual function when the paintable is in an incomplete state (like a
GtkMediaStream before receiving the first frame).
“invalidate-contents”
signalvoid user_function (GdkPaintable *paintable, gpointer user_data)
Emitted when the contents of the paintable
change.
Examples for such an event would be videos changing to the next frame or the icon theme for an icon changing.
Flags: Run Last
“invalidate-size”
signalvoid user_function (GdkPaintable *paintable, gpointer user_data)
Emitted when the intrinsic size of the paintable
changes. This means the values
reported by at least one of gdk_paintable_get_intrinsic_width()
,
gdk_paintable_get_intrinsic_height()
or gdk_paintable_get_intrinsic_aspect_ratio()
has changed.
Examples for such an event would be a paintable displaying the contents of a toplevel surface being resized.
Flags: Run Last