Tk_GetVisual(3) Tk Library Procedures Tk_GetVisual(3)

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NAME

Tk_GetVisual - translate from string to visual

SYNOPSIS

#include <tk.h>

Visual *
Tk_GetVisual(interp, tkwin, string, depthPtr, colormapPtr)

ARGUMENTS

Tcl_Interp *interp (in) Interpreter to use for error
reporting.

Tk_Window tkwin (in) Token for window in which the
visual will be used.

const char *string (in) String that identifies the
desired visual. See below for
valid formats.

int *depthPtr (out) Depth of returned visual gets
stored here.

Colormap *colormapPtr (out) If non-NULL then a suitable
colormap for visual is found
and its identifier is stored
here.
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DESCRIPTION

Tk_GetVisual takes a string description of a visual and finds a
suitable X Visual for use in tkwin, if there is one. It returns a
pointer to the X Visual structure for the visual and stores the
number of bits per pixel for it at *depthPtr. If string is
unrecognizable or if no suitable visual could be found, then NULL is
returned and Tk_GetVisual leaves an error message in interpreter
interp's result. If colormap is non-NULL then Tk_GetVisual also
locates an appropriate colormap for use with the result visual and
stores its X identifier at *colormapPtr.

The string argument specifies the desired visual in one of the
following ways:

class depth The string consists of a class name followed by an
integer depth, with any amount of white space
(including none) in between. class selects what sort
of visual is desired and must be one of directcolor,
grayscale, greyscale, pseudocolor, staticcolor,
staticgray, staticgrey, or truecolor, or a unique
abbreviation. depth specifies how many bits per pixel
are needed for the visual. If possible, Tk_GetVisual
will return a visual with this depth; if there is no
visual of the desired depth then Tk_GetVisual looks
first for a visual with greater depth, then one with
less depth.

default Use the default visual for tkwin's screen.

pathName Use the visual for the window given by pathName.
pathName must be the name of a window on the same
screen as tkwin.

number Use the visual whose X identifier is number.

best ?depth? Choose the "best possible" visual, using the following
rules, in decreasing order of priority:

(a) a visual that has exactly the desired depth is
best, followed by a visual with greater depth
than requested (but as little extra as
possible), followed by a visual with less depth
than requested (but as great a depth as
possible);

(b) if no depth is specified, then the deepest
available visual is chosen;

(c) pseudocolor is better than truecolor or
directcolor, which are better than staticcolor,
which is better than staticgray or grayscale;

(d) the default visual for the screen is better
than any other visual.

CREDITS

The idea for Tk_GetVisual, and the first implementation, came from
Paul Mackerras.

KEYWORDS

colormap, screen, visual

Tk 4.0 Tk_GetVisual(3)