If the desired property is not
present: Create a colormap (unless you are using the default colormap of
the screen). Determine the color characteristics of the visual. Allocate
cells in the colormap (or create it with AllocAll). Call XStoreColors
to store appropriate color values in the colormap. Fill in the descriptive
members in the XStandardColormap structure. Attach the property to the
root window. Use XSetCloseDownMode to make the resource permanent.
- 5.
- Ungrab
the server.
XSetRGBColormaps can generate BadAlloc, BadAtom, and BadWindow
errors.
The XGetRGBColormaps function returns the RGB colormap definitions
stored in the specified property on the named window. If the property exists,
is of type RGB_COLOR_MAP, is of format 32, and is long enough to contain
a colormap definition, XGetRGBColormaps allocates and fills in space
for the returned colormaps and returns a nonzero status. If the visualid
is not present, XGetRGBColormaps assumes the default visual for the
screen on which the window is located; if the killid is not present,
None is assumed, which indicates that the resources cannot be released.
Otherwise, none of the fields are set, and XGetRGBColormaps returns
a zero status. Note that it is the caller's responsibility to honor the ICCCM
restriction that only RGB_DEFAULT_MAP contain more than one definition.
XGetRGBColormaps can generate BadAtom and BadWindow errors.
The
XStandardColormap structure contains:
/* Hints */
| #define |
ReleaseByFreeingColormap
| T} T{ |
| ( (XID) 1L); |
| T} |
/* Values */
0
0>=40 .vs 0u
0<=39 .vs 0p
typedef struct {
Colormap colormap;
unsigned long red_max;
unsigned long red_mult;
unsigned long green_max;
unsigned long green_mult;
unsigned long blue_max;
unsigned long blue_mult;
unsigned long base_pixel;
VisualID visualid;
XID killid;
} XStandardColormap;
The colormap member is the colormap created by the XCreateColormap function.
The red_max, green_max, and blue_max members give the maximum red, green,
and blue values, respectively. Each color coefficient ranges from zero
to its max, inclusive. For example, a common colormap allocation is 3/3/2
(3 planes for red, 3 planes for green, and 2 planes for blue). This colormap
would have red_max = 7, green_max = 7, and blue_max = 3. An alternate
allocation that uses only 216 colors is red_max = 5, green_max = 5, and
blue_max = 5.
The red_mult, green_mult, and blue_mult members give the scale
factors used to compose a full pixel value. (See the discussion of the
base_pixel members for further information.); For a 3/3/2 allocation, red_mult
might be 32, green_mult might be 4, and blue_mult might be 1. For a 6-colors-each
allocation, red_mult might be 36, green_mult might be 6, and blue_mult
might be 1.
The base_pixel member gives the base pixel value used to compose
a full pixel value. Usually, the base_pixel is obtained from a call to
the XAllocColorPlanes function. Given integer red, green, and blue
coefficients in their appropriate ranges, one then can compute a corresponding
pixel value by using the following expression:
0
0>=40 .vs 0u
0<=39 .vs 0p
(r * red_mult + g * green_mult + b * blue_mult + base_pixel) & 0xFFFFFFFF
For GrayScale colormaps, only the colormap, red_max, red_mult, and
base_pixel members are defined. The other members are ignored. To compute
a GrayScale pixel value, use the following expression:
0
0>=40 .vs 0u
0<=39 .vs 0p
(gray * red_mult + base_pixel) & 0xFFFFFFFF
Negative multipliers can be represented by converting the 2's complement
representation of the multiplier into an unsigned long and storing the
result in the appropriate _mult field. The step of masking by 0xFFFFFFFF
effectively converts the resulting positive multiplier into a negative
one. The masking step will take place automatically on many machine architectures,
depending on the size of the integer type used to do the computation,
The
visualid member gives the ID number of the visual from which the colormap
was created. The killid member gives a resource ID that indicates whether
the cells held by this standard colormap are to be released by freeing
the colormap ID or by calling the XKillClient function on the indicated
resource. (Note that this method is necessary for allocating out of an existing
colormap.);
The properties containing the XStandardColormap information
have the type RGB_COLOR_MAP.
- BadAlloc
- The server failed to
allocate the requested resource or server memory.
- BadAtom
- A value for
an Atom argument does not name a defined Atom.
- BadWindow
- A value for a
Window argument does not name a defined Window.
XAllocColor(3X11)
,
XCreateColormap(3X11)
, XFree(3X11)
, XSetCloseDownMode(3X11)
Xlib - C Language X Interface
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