https://invisible-island.net/xterm/xtoolkit/
XtAllocateGC - obtain a sharable GC with modifiable fields
#include <X11/Intrinsic.h>
GC XtAllocateGC(Widget w, Cardinal depth, XtGCMask value_mask, XGCVal-
ues *values, XtGCMask dynamic_mask, XtGCMask unused_mask);
values Specifies the actual values for this GC.
value_mask
Specifies which fields of the values are specified.
w Specifies the widget.
depth Specifies the depth for which the returned GC is valid, or 0.
dynamic_mask
Specifies the fields of the GC that will be modified by the
caller.
unused_mask
Specifies the fields of the GC that will not be needed by the
caller.
The XtAllocateGC function returns a sharable GC that may be modified by
the client. The screen field of the specified widget or of the nearest
widget ancestor of the specified object and the specified depth argu-
ment supply the root and drawable depths for which the GC is to be
valid. If depth is zero the depth is taken from the depth field of the
specified widget or of the nearest widget ancestor of the specified
object.
The value_mask argument specifies the fields of the GC that will be
initialized with the respective members of the values structure. The
dynamic_mask argument specifies fields that the caller intends to mod-
ify during program execution. The caller must ensure that the corre-
sponding GC field is set prior to each use of the GC. The unused_mask
argument specifies fields of the GC that are of no interest to the
caller. The caller may make no assumptions about the contents of any
fields specified in unused_mask. The caller may assume that at all
times all fields not specified in either dynamic_mask or unused_mask
have their default value if not specified in value_mask or the value
specified by values. If a field is specified in both value_mask and
dynamic_mask, the effect is as if it were specified only in
dynamic_mask and then immediately set to the value in values. If a
field is set in unused_mask and also in either value_mask or
dynamic_mask, the specification in unused_mask is ignored.
XtAllocateGC tries to minimize the number of unique GCs created by com-
paring the arguments with those of previous calls and returning an
existing GC when there are no conflicts. XtAllocateGC may modify and
return an existing GC if it was allocated with a nonzero unused_mask.
XtGetGC
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtAllocateGC(3)