libtk/doc/GetVisual.3

#include <tk.h>
Visual *
Tk_GetVisual(interp, tkwin, string, depthPtr, colormapPtr)
 ARGUMENTS
.AS "Tcl_Interp" *colormapPtr
.AP Tcl_Interp *interp in
Interpreter to use for error reporting.
.AP Tk_Window tkwin in
Token for window in which the visual will be used.
.AP char *string in
String that identifies the desired visual. See below for
valid formats.
.AP int *depthPtr out
Depth of returned visual gets stored here.
.AP Colormap *colormapPtr out
If non-NULL then a suitable colormap for visual is found and its
identifier is stored here.
E
 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 interp->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:
 15
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.
 15
default
Use the default visual for tkwin's screen.
 15
pathName
Use the visual for the window given by pathName.
pathName must be the name of a window on the same screen
as tkwin.
 15
number
Use the visual whose X identifier is number.
 15
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