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(Color Parameters): Document alpha parameter.

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Chong Yidong 2008-11-18 07:05:36 +00:00
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commit d9ce48d618
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doc/lispref/frames.texi
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@ -230,6 +230,8 @@ only the @code{height}, @code{width}, @code{name}, @code{title},
parameters do something special. If the terminal supports colors, the
parameters @code{foreground-color}, @code{background-color},
@code{background-mode} and @code{display-type} are also meaningful.
If the terminal supports frame transparency, the parameter
@code{alpha} is also meaningful.
You can use frame parameters to define frame-local bindings for
variables. @xref{Frame-Local Variables}.
@ -748,6 +750,27 @@ If your monitor displays colors too light, you should specify a
@code{screen-gamma} value smaller than 2.2. This requests correction
that makes colors darker. A screen gamma value of 1.5 may give good
results for LCD color displays.
@item alpha
@cindex opacity, frame
@cindex transparency, frame
@vindex frame-alpha-lower-limit
This parameter specifies the opacity of the frame, on graphical
displays that support variable opacity. It should be an integer
between 0 and 100, where 0 means completely transparent and 100 means
completely opaque. It can also have a @code{nil} value, which tells
Emacs not to set the frame opacity (leaving it to the window manager).
To prevent the frame from disappearing completely from view, the
variable @var{frame-alpha-lower-limit} defines a lower opacity limit.
If the value of the frame parameter is less than the value of this
variable, Emacs uses the latter. By default,
@var{frame-alpha-lower-limit} is 20.
The @code{alpha} frame parameter can also be a cons cell
@code{(@samp{active} . @samp{inactive})}, where @samp{active} is the
opacity of the frame when it is selected, and @samp{inactive} is the
opactity when it is not selected.
@end table
These frame parameters are semi-obsolete in that they are automatically