1Tk_GetVisual(3) Tk Library Procedures Tk_GetVisual(3)
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8 Tk_GetVisual - translate from string to visual
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11 #include <tk.h>
12 Visual *
14 Tk_GetVisual(interp, tkwin, string, depthPtr, colormapPtr)
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17 Tcl_Interp *interp (in) Interpreter to use for error re‐
18 porting.
19 Tk_Window tkwin (in) Token for window in which the
21 visual will be used.
22 const char *string (in) String that identifies the de‐
24 sired visual. See below for
25 valid formats.
26 int *depthPtr (out) Depth of returned visual gets
28 stored here.
29 Colormap *colormapPtr (out) If non-NULL then a suitable col‐
31 ormap for visual is found and its
32 identifier is stored here.
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36 Tk_GetVisual takes a string description of a visual and finds a suit‐
37 able X Visual for use in tkwin, if there is one. It returns a pointer
38 to the X Visual structure for the visual and stores the number of bits
39 per pixel for it at *depthPtr. If string is unrecognizable or if no
40 suitable visual could be found, then NULL is returned and Tk_GetVisual
41 leaves an error message in interpreter interp's result. If colormap is
42 non-NULL then Tk_GetVisual also locates an appropriate colormap for use
43 with the result visual and stores its X identifier at *colormapPtr.
44 The string argument specifies the desired visual in one of the follow‐
46 ing ways:
47 class depth The string consists of a class name followed by an inte‐
49 ger depth, with any amount of white space (including
50 none) in between. class selects what sort of visual is
51 desired and must be one of directcolor, grayscale,
52 greyscale, pseudocolor, staticcolor, staticgray, static‐
53 grey, or truecolor, or a unique abbreviation. depth
54 specifies how many bits per pixel are needed for the
55 visual. If possible, Tk_GetVisual will return a visual
56 with this depth; if there is no visual of the desired
57 depth then Tk_GetVisual looks first for a visual with
58 greater depth, then one with less depth.
59 default Use the default visual for tkwin's screen.
61 pathName Use the visual for the window given by pathName. path‐
63 Name must be the name of a window on the same screen as
64 tkwin.
65 number Use the visual whose X identifier is number.
67 best ?depth? Choose the “best possible” visual, using the following
69 rules, in decreasing order of priority:
70 (a) a visual that has exactly the desired depth is
72 best, followed by a visual with greater depth
73 than requested (but as little extra as possible),
74 followed by a visual with less depth than re‐
75 quested (but as great a depth as possible);
76 (b) if no depth is specified, then the deepest avail‐
78 able visual is chosen;
79 (c) pseudocolor is better than truecolor or direct‐
81 color, which are better than staticcolor, which
82 is better than staticgray or grayscale;
83 (d) the default visual for the screen is better than
85 any other visual.
86
88 The idea for Tk_GetVisual, and the first implementation, came from Paul
89 Mackerras.
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92 colormap, screen, visual
93Tk 4.0 Tk_GetVisual(3)