Tk_GetVisual - translate from string to visual
Tk_GetVisual(interp, tkwin, string, depthPtr, colormapPtr)
- 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
- 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.
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:
- 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.
- Use the default visual for tkwin's screen.
- Use the visual for the window given by pathName. pathName
must be the name of a window on the same screen as tkwin.
- 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 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
- if no depth is specified, then the deepest available visual is
- pseudocolor is better than truecolor or directcolor,
which are better than staticcolor, which is better than
staticgray or grayscale;
- the default visual for the screen is better than any other visual.
The idea for Tk_GetVisual, and the first implementation, came from Paul
colormap, screen, visual