3.2.3 Gravity Attributes
The bit gravity of a window defines which region of the window should be
retained when an
InputOutput
window is resized.
The default value for the bit-gravity attribute is
ForgetGravity.
The window gravity of a window allows you to define how the
InputOutput
or
InputOnly
window should be repositioned if its parent is resized.
The default value for the
win-gravity attribute is
NorthWestGravity .
If the inside height of a window is not changed
and if the window is moved or its border is changed,
then the contents of the window are not lost but move with the window.
Changing the inside width or
height of the window causes its contents to be
moved or lost (depending on the bit-gravity of the window) and causes
children to be reconfigured (depending on their win-gravity).
For a
change of width and height, the (x, y) pairs are defined:
|
| Gravity Direction | Coordinates
|
|---|
|
| NorthWestGravity | (0, 0)
|
| NorthGravity | (Width/2, 0)
|
| NorthEastGravity | (Width, 0)
|
| WestGravity | (0, Height/2)
|
| CenterGravity | (Width/2, Height/2)
|
| EastGravity | (Width, Height/2)
|
| SouthWestGravity | (0, Height)
|
| SouthGravity | (Width/2, Height)
|
| SouthEastGravity | (Width, Height)
|
When a window with one of these bit-gravity values is resized,
the corresponding pair
defines the change in position of each pixel in the window.
When a window with one of these win-gravities has its parent window resized,
the corresponding pair defines the change in position of the window
within the parent.
When a window is so repositioned, a
GravityNotify
event is generated.
A bit-gravity of
StaticGravity
indicates that the contents or origin should not move relative to the
origin of the root window.
If the change in size of the window is coupled with a change in position (x, y),
then for bit-gravity the change in position of each pixel is (-x, -y), and for
win-gravity the change in position of a child when its parent is so resized is
(-x, -y).
Note that
StaticGravity
still only takes effect when the width or height of the window is changed,
not when the window is moved.
A bit-gravity of
ForgetGravity
indicates that the window's contents are always discarded after a size change,
even if a backing store or save under has been requested.
The window is tiled with its background
and zero or more
Expose
events are generated.
If no background is defined, the existing screen contents are not
altered.
Some X servers may also ignore the specified bit-gravity and
always generate
Expose
events.
The contents and borders of inferiors are not affected by their parent's
bit-gravity.
A server is permitted to ignore the specified bit-gravity and use
Forget
instead.
A win-gravity of
UnmapGravity
is like
NorthWestGravity
(the window is not moved),
except the child is also
unmapped when the parent is resized,
and an
UnmapNotify
event is
generated.
Christophe Tronche, [email protected]
