Tk_AllocColorFromObj(3) Tk Library Procedures Tk_AllocColorFromObj(3)
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NAME
Tk_AllocColorFromObj, Tk_GetColor, Tk_GetColorFromObj, Tk_GetColorByValue, Tk_NameOfColor, Tk_Free-ColorFromObj, Tk_FreeColorFromObj,
ColorFromObj, Tk_FreeColor - maintain database of colors
SYNOPSIS
#include <tk.h>
XColor * |
Tk_AllocColorFromObj(interp, tkwin, objPtr) |
XColor * |
Tk_GetColor(interp, tkwin, name) |
XColor * |
Tk_GetColorFromObj(tkwin, objPtr) |
XColor *
Tk_GetColorByValue(tkwin, prefPtr)
CONST char *
Tk_NameOfColor(colorPtr)
GC
Tk_GCForColor(colorPtr, drawable)
Tk_FreeColorFromObj(tkwin, objPtr) |
Tk_FreeColor(colorPtr)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for error reporting.
Tk_Window tkwin (in) Token for window in which color will be used.
Tcl_Obj *objPtr (in/out) ||
String value describes desired color; internal rep will be modi- |
fied to cache pointer to corresponding (XColor *). |
char *name (in) ||
Same as objPtr except description of color is passed as a string |
and resulting (XColor *) isn't cached.
XColor *prefPtr (in) Indicates red, green, and blue intensities of desired color.
XColor *colorPtr (in) Pointer to X color information. Must have been allocated by pre-vious previous
vious call to Tk_AllocColorFromObj, Tk_GetColor or Tk_GetColorBy-Value, Tk_GetColorByValue,
Value, except when passed to Tk_NameOfColor.
Drawable drawable (in) Drawable in which the result graphics context will be used. Must
have same screen and depth as the window for which the color was
allocated.
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DESCRIPTION
These procedures manage the colors being used by a Tk application. They allow colors to be shared |
whenever possible, so that colormap space is preserved, and they pick closest available colors when |
colormap space is exhausted. |
Given a textual description of a color, Tk_AllocColorFromObj locates a pixel value that may be used |
to render the color in a particular window. The desired color is specified with an object whose |
string value must have one of the following forms:
colorname Any of the valid textual names for a color defined in the server's color database
file, such as red or PeachPuff.
#RGB
#RRGGBB
#RRRGGGBBB
#RRRRGGGGBBBB A numeric specification of the red, green, and blue intensities to use to display
the color. Each R, G, or B represents a single hexadecimal digit. The four
forms permit colors to be specified with 4-bit, 8-bit, 12-bit or 16-bit values.
When fewer than 16 bits are provided for each color, they represent the most sig-nificant significant
nificant bits of the color. For example, #3a7 is the same as #3000a0007000.
Tk_AllocColorFromObj returns a pointer to an XColor structure; the structure indicates the exact |
intensities of the allocated color (which may differ slightly from those requested, depending on the |
limitations of the screen) and a pixel value that may be used to draw with the color in tkwin. If an |
error occurs in Tk_AllocColorFromObj (such as an unknown color name) then NULL is returned and an |
error message is stored in interp's result if interp isn't NULL. If the colormap for tkwin is full, |
Tk_AllocColorFromObj will use the closest existing color in the colormap. Tk_AllocColorFromObj |
caches information about the return value in objPtr, which speeds up future calls to procedures such |
as Tk_AllocColorFromObj and Tk_GetColorFromObj. |
Tk_GetColor is identical to Tk_AllocColorFromObj except that the description of the color is speci- |
fied with a string instead of an object. This prevents Tk_GetColor from caching the return value, so |
Tk_GetColor is less efficient than Tk_AllocColorFromObj. |
Tk_GetColorFromObj returns the token for an existing color, given the window and description used to |
create the color. Tk_GetColorFromObj doesn't actually create the color; the color must already have |
been created with a previous call to Tk_AllocColorFromObj or Tk_GetColor. The return value is cached |
in objPtr, which speeds up future calls to Tk_GetColorFromObj with the same objPtr and tkwin.
Tk_GetColorByValue is similar to Tk_GetColor except that the desired color is indicated with the red,
green, and blue fields of the structure pointed to by colorPtr.
This package maintains a database of all the colors currently in use. If the same color is requested
multiple times from Tk_GetColor or Tk_AllocColorFromObj (e.g. by different windows), or if the same
intensities are requested multiple times from Tk_GetColorByValue, then existing pixel values will be
re-used. Re-using an existing pixel avoids any interaction with the window server, which makes the
allocation much more efficient. These procedures also provide a portable interface that works across
all platforms. For this reason, you should generally use Tk_AllocColorFromObj, Tk_GetColor, or
Tk_GetColorByValue instead of lower level procedures like XAllocColor.
Since different calls to this package may return the same shared pixel value, callers should never
change the color of a pixel returned by the procedures. If you need to change a color value dynami-cally, dynamically,
cally, you should use XAllocColorCells to allocate the pixel value for the color.
The procedure Tk_NameOfColor is roughly the inverse of Tk_GetColor. If its colorPtr argument was
created by Tk_AllocColorFromObj or Tk_GetColor then the return value is the string that was used to
create the color. If colorPtr was created by a call to Tk_GetColorByValue, or by any other mecha-nism, mechanism,
nism, then the return value is a string that could be passed to Tk_GetColor to return the same color.
Note: the string returned by Tk_NameOfColor is only guaranteed to persist until the next call to
Tk_NameOfColor.
Tk_GCForColor returns a graphics context whose foreground field is the pixel allocated for colorPtr
and whose other fields all have default values. This provides an easy way to do basic drawing with a
color. The graphics context is cached with the color and will exist only as long as colorPtr exists;
it is freed when the last reference to colorPtr is freed by calling Tk_FreeColor.
When a color is no longer needed Tk_FreeColorFromObj or Tk_FreeColor should be called to release it. |
For Tk_FreeColorFromObj the color to release is specified with the same information used to create |
it; for Tk_FreeColor the color to release is specified with a pointer to its XColor structure. There |
should be exactly one call to Tk_FreeColorFromObj or Tk_FreeColor for each call to Tk_AllocColorFro- |
mObj, Tk_GetColor, or Tk_GetColorByValue.
KEYWORDS
color, intensity, object, pixel value
Tk 8.1 Tk_AllocColorFromObj(3)
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