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Tk Library Procedures Tk_AllocColorFromObj(3TK)

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NAME

Tk_AllocColorFromObj, Tk_GetColor, Tk_GetColorFromObj,

Tk_GetColorByValue, Tk_NameOfColor, Tk_FreeColorFromObj,

Tk_FreeColor - maintain database of colors

SYNOPSIS

#include

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)

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 modified 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. Tk Last change: 8.1 1

Tk Library Procedures Tk_AllocColorFromObj(3TK)

XColor *prefPtr (in) Indicates red, green, and blue intensities of desired color.

XColor *colorPtr (in) Pointer to X color infor-

mation. Must have been allocated by previous call to

Tk_AllocColorFromObj,

Tk_GetColor or

Tk_GetColorByValue,

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 appli- |

cation. 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

Tk Last change: 8.1 2

Tk Library Procedures Tk_AllocColorFromObj(3TK)

are provided for each color, they represent the most significant bits of

the color. For example, #3a7 is the

same as #3000a0007000.

Tk_AllocColorFromObj returns a pointer to an XColor struc- |

ture; 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 specified with a string |

instead of an object. This prevents Tk_GetColor from cach- |

ing 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 dif-

ferent 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 pro-

vide 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 Tk Last change: 8.1 3

Tk Library Procedures Tk_AllocColorFromObj(3TK)

a pixel returned by the procedures. If you need to change a color value dynamically, 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

mechanism, 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 per-

sist 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_AllocColorFromObj, Tk_GetColor, or Tk_GetColorByValue.

KEYWORDS color, intensity, object, pixel value

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

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| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | runtime/tk-8 |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for Tk is available on http://opensolaris.org. Tk Last change: 8.1 4