XAllocColor(3) XLIB FUNCTIONS XAllocColor(3)NAME
XAllocColor, XAllocNamedColor, XAllocColorCells, XAllocColorPlanes,
XFreeColors - allocate and free colors
SYNTAX
Status XAllocColor(Display *display, Colormap colormap, XColor
*screen_in_out);
Status XAllocNamedColor(Display *display, Colormap colormap, char
*color_name, XColor *screen_def_return, XColor
*exact_def_return);
Status XAllocColorCells(Display *display, Colormap colormap, Bool con‐
tig, unsigned long plane_masks_return[], unsigned int nplanes,
unsigned long pixels_return[], unsigned int npixels);
Status XAllocColorPlanes(Display *display, Colormap colormap, Bool con‐
tig, unsigned long pixels_return[], int ncolors, int nreds, int
ngreens, int nblues, unsigned long *rmask_return, unsigned long
*gmask_return, unsigned long *bmask_return);
int XFreeColors(Display *display, Colormap colormap, unsigned long pix‐
els[], int npixels, unsigned long planes);
color_name
Specifies the color name string (for example, red) whose
color definition structure you want returned.
colormap Specifies the colormap.
contig Specifies a Boolean value that indicates whether the planes
must be contiguous.
display Specifies the connection to the X server.
exact_def_return
Returns the exact RGB values.
ncolors Specifies the number of pixel values that are to be returned
in the pixels_return array.
npixels Specifies the number of pixels.
nplanes Specifies the number of plane masks that are to be returned
in the plane masks array.
nreds
ngreens
nblues
Specify the number of red, green, and blue planes. The value
you pass must be nonnegative.
pixels Specifies an array of pixel values.
pixels_return
Returns an array of pixel values.
plane_mask_return
Returns an array of plane masks.
planes Specifies the planes you want to free.
rmask_return
gmask_return
bmask_return
Return bit masks for the red, green, and blue planes.
screen_def_return
Returns the closest RGB values provided by the hardware.
screen_in_out
Specifies and returns the values actually used in the col‐
ormap.
DESCRIPTION
The XAllocColor function allocates a read-only colormap entry corre‐
sponding to the closest RGB value supported by the hardware. XAlloc‐
Color returns the pixel value of the color closest to the specified RGB
elements supported by the hardware and returns the RGB value actually
used. The corresponding colormap cell is read-only. In addition, XAl‐
locColor returns nonzero if it succeeded or zero if it failed. Multi‐
ple clients that request the same effective RGB value can be assigned
the same read-only entry, thus allowing entries to be shared. When the
last client deallocates a shared cell, it is deallocated. XAllocColor
does not use or affect the flags in the XColor structure.
XAllocColor can generate a BadColor error.
The XAllocNamedColor function looks up the named color with respect to
the screen that is associated with the specified colormap. It returns
both the exact database definition and the closest color supported by
the screen. The allocated color cell is read-only. The pixel value is
returned in screen_def_return. If the color name is not in the Host
Portable Character Encoding, the result is implementation-dependent.
Use of uppercase or lowercase does not matter. If screen_def_return
and exact_def_return point to the same structure, the pixel field will
be set correctly, but the color values are undefined. XAllocNamedColor
returns nonzero if a cell is allocated; otherwise, it returns zero.
XAllocNamedColor can generate a BadColor error.
The XAllocColorCells function allocates read/write color cells. The
number of colors must be positive and the number of planes nonnegative,
or a BadValue error results. If ncolors and nplanes are requested,
then ncolors pixels and nplane plane masks are returned. No mask will
have any bits set to 1 in common with any other mask or with any of the
pixels. By ORing together each pixel with zero or more masks, ncolors
* 2nplanes distinct pixels can be produced. All of these are allocated
writable by the request. For GrayScale or PseudoColor, each mask has
exactly one bit set to 1. For DirectColor, each has exactly three bits
set to 1. If contig is True and if all masks are ORed together, a sin‐
gle contiguous set of bits set to 1 will be formed for GrayScale or
PseudoColor and three contiguous sets of bits set to 1 (one within each
pixel subfield) for DirectColor. The RGB values of the allocated
entries are undefined. XAllocColorCells returns nonzero if it suc‐
ceeded or zero if it failed.
XAllocColorCells can generate BadColor and BadValue errors.
The specified ncolors must be positive; and nreds, ngreens, and nblues
must be nonnegative, or a BadValue error results. If ncolors colors,
nreds reds, ngreens greens, and nblues blues are requested, ncolors
pixels are returned; and the masks have nreds, ngreens, and nblues bits
set to 1, respectively. If contig is True, each mask will have a con‐
tiguous set of bits set to 1. No mask will have any bits set to 1 in
common with any other mask or with any of the pixels. For DirectColor,
each mask will lie within the corresponding pixel subfield. By ORing
together subsets of masks with each pixel value, ncolors *
2(nreds+ngreens+nblues) distinct pixel values can be produced. All of
these are allocated by the request. However, in the colormap, there
are only ncolors * 2nreds independent red entries, ncolors * 2ngreens
independent green entries, and ncolors * 2nblues independent blue
entries. This is true even for PseudoColor. When the colormap entry
of a pixel value is changed (using XStoreColors, XStoreColor, or
XStoreNamedColor), the pixel is decomposed according to the masks, and
the corresponding independent entries are updated. XAllocColorPlanes
returns nonzero if it succeeded or zero if it failed.
XAllocColorPlanes can generate BadColor and BadValue errors.
The XFreeColors function frees the cells represented by pixels whose
values are in the pixels array. The planes argument should not have
any bits set to 1 in common with any of the pixels. The set of all
pixels is produced by ORing together subsets of the planes argument
with the pixels. The request frees all of these pixels that were allo‐
cated by the client (using XAllocColor, XAllocNamedColor, XAllocColor‐
Cells, and XAllocColorPlanes). Note that freeing an individual pixel
obtained from XAllocColorPlanes may not actually allow it to be reused
until all of its related pixels are also freed. Similarly, a read-only
entry is not actually freed until it has been freed by all clients, and
if a client allocates the same read-only entry multiple times, it must
free the entry that many times before the entry is actually freed.
All specified pixels that are allocated by the client in the colormap
are freed, even if one or more pixels produce an error. If a specified
pixel is not a valid index into the colormap, a BadValue error results.
If a specified pixel is not allocated by the client (that is, is unal‐
located or is only allocated by another client) or if the colormap was
created with all entries writable (by passing AllocAll to XCreateCol‐
ormap), a BadAccess error results. If more than one pixel is in error,
the one that gets reported is arbitrary.
XFreeColors can generate BadAccess, BadColor, and BadValue errors.
DIAGNOSTICS
BadAccess A client attempted to free a color map entry that it did not
already allocate.
BadAccess A client attempted to store into a read-only color map entry.
BadColor A value for a Colormap argument does not name a defined Col‐
ormap.
BadValue Some numeric value falls outside the range of values accepted
by the request. Unless a specific range is specified for an
argument, the full range defined by the argument's type is
accepted. Any argument defined as a set of alternatives can
generate this error.
SEE ALSOXCreateColormap(3), XQueryColor(3), XStoreColors(3)
Xlib - C Language X Interface
X Version 11 libX11 1.6.2 XAllocColor(3)
