XCreateGC.man revision 0ba404d1 
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 t
 XCreateGC __libmansuffix__ __xorgversion__ "XLIB FUNCTIONS"
 NAME
XCreateGC, XCopyGC, XChangeGC, XGetGCValues, XFreeGC, XGContextFromGC, XGCValues - create or free graphics contexts and graphics context structure

 SYNTAX

GC XCreateGC\^(\^Display *display\^, Drawable d\^, unsigned long
valuemask\^, XGCValues *\^values\^);


int XCopyGC\^(\^Display *display\^, GC src\^,
unsigned long valuemask\^, GC dest\^);


int XChangeGC\^(\^Display *display\^, GC gc\^, unsigned long
valuemask\^, XGCValues *\^values\^);


Status XGetGCValues\^(\^Display *display\^, GC gc\^, unsigned long
valuemask\^, XGCValues *values_return\^);


int XFreeGC\^(\^Display *display\^, GC gc\^);


GContext XGContextFromGC\^(\^GC gc\^);

 ARGUMENTS
 d 1i
Specifies the drawable.

 dest 1i
Specifies the destination GC.

 display 1i
Specifies the connection to the X server.

 gc 1i
Specifies the GC.

 src 1i
Specifies the components of the source GC.

 valuemask 1i
Specifies which components in the GC are to be set, copied, changed, or returned.
This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.

 values 1i
Specifies any values as specified by the valuemask.

 values_return 1i
Returns the GC values in the specified
 XGCValues structure.

 DESCRIPTION
The
 XCreateGC function creates a graphics context and returns a GC.
The GC can be used with any destination drawable having the same root
and depth as the specified drawable.
Use with other drawables results in a
 BadMatch error.


 XCreateGC can generate
 BadAlloc ,  BadDrawable ,  BadFont ,  BadMatch ,  BadPixmap , and
 BadValue errors.


The
 XCopyGC function copies the specified components from the source GC
to the destination GC.
The source and destination GCs must have the same root and depth,
or a
 BadMatch error results.
The valuemask specifies which component to copy, as for
 XCreateGC . 

 XCopyGC can generate
 BadAlloc ,  BadGC , and
 BadMatch errors.


The
 XChangeGC function changes the components specified by valuemask for
the specified GC.
The values argument contains the values to be set.
The values and restrictions are the same as for
 XCreateGC . Changing the clip-mask overrides any previous
 XSetClipRectangles request on the context.
Changing the dash-offset or dash-list
overrides any previous
 XSetDashes request on the context.
The order in which components are verified and altered is server dependent.
If an error is generated, a subset of the components may have been altered.


 XChangeGC can generate
 BadAlloc ,  BadFont ,  BadGC ,  BadMatch ,  BadPixmap , and
 BadValue errors.


The
 XGetGCValues function returns the components specified by valuemask for the specified GC.
If the valuemask contains a valid set of GC mask bits

n ( GCFunction ,
 GCPlaneMask ,  GCForeground ,  GCBackground ,  GCLineWidth ,  GCLineStyle ,  GCCapStyle ,  GCJoinStyle ,  GCFillStyle ,  GCFillRule ,  GCTile ,  GCStipple ,  GCTileStipXOrigin ,  GCTileStipYOrigin ,  GCFont ,  GCSubwindowMode ,  GCGraphicsExposures ,  GCClipXOrigin ,  GCCLipYOrigin ,  GCDashOffset , or
 GCArcMode ) and no error occurs,
 XGetGCValues sets the requested components in values_return and returns a nonzero status.
Otherwise, it returns a zero status.
Note that the clip-mask and dash-list (represented by the
 GCClipMask and
 GCDashList bits, respectively, in the valuemask)
cannot be requested.
Also note that an invalid resource ID (with one or more of the three
most significant bits set to 1) will be returned for
 GCFont ,  GCTile , and
 GCStipple if the component has never been explicitly set by the client.


The
 XFreeGC function destroys the specified GC as well as all the associated storage.


 XFreeGC can generate a
 BadGC error.

 STRUCTURES
The
 XGCValues structure contains:


/* GC attribute value mask bits */



#define 
 GCFunction T} T{
(1L<<0)
T}
#define T{
 GCPlaneMask T} T{
(1L<<1)
T}
#define T{
 GCForeground T} T{
(1L<<2)
T}
#define T{
 GCBackground T} T{
(1L<<3)
T}
#define T{
 GCLineWidth T} T{
(1L<<4)
T}
#define T{
 GCLineStyle T} T{
(1L<<5)
T}
#define T{
 GCCapStyle T} T{
(1L<<6)
T}
#define T{
 GCJoinStyle T} T{
(1L<<7)
T}
#define T{
 GCFillStyle T} T{
(1L<<8)
T}
#define T{
 GCFillRule T} T{
(1L<<9)
T}
#define T{
 GCTile T} T{
(1L<<10)
T}
#define T{
 GCStipple T} T{
(1L<<11)
T}
#define T{
 GCTileStipXOrigin T} T{
(1L<<12)
T}
#define T{
 GCTileStipYOrigin T} T{
(1L<<13)
T}
#define T{
 GCFont T} T{
(1L<<14)
T}
#define T{
 GCSubwindowMode T} T{
(1L<<15)
T}
#define T{
 GCGraphicsExposures T} T{
(1L<<16)
T}
#define T{
 GCClipXOrigin T} T{
(1L<<17)
T}
#define T{
 GCClipYOrigin T} T{
(1L<<18)
T}
#define T{
 GCClipMask T} T{
(1L<<19)
T}
#define T{
 GCDashOffset T} T{
(1L<<20)
T}
#define T{
 GCDashList T} T{
(1L<<21)
T}
#define T{
 GCArcMode T} T{
(1L<<22)
T}
.TE
N "XGCValues" "" "@DEF@" 

.EX
/* Values */

typedef struct {
 int function; /* logical operation */
 unsigned long plane_mask; /* plane mask */
 unsigned long foreground; /* foreground pixel */
 unsigned long background; /* background pixel */
 int line_width; /* line width (in pixels) */
 int line_style; /* LineSolid, LineOnOffDash, LineDoubleDash */
 int cap_style; /* CapNotLast, CapButt, CapRound, CapProjecting */
 int join_style; /* JoinMiter, JoinRound, JoinBevel */
 int fill_style; /* FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
 int fill_rule; /* EvenOddRule, WindingRule */
 int arc_mode; /* ArcChord, ArcPieSlice */
 Pixmap tile; /* tile pixmap for tiling operations */
 Pixmap stipple; /* stipple 1 plane pixmap for stippling */
 int ts_x_origin; /* offset for tile or stipple operations */
 int ts_y_origin;
 Font font; /* default text font for text operations */
 int subwindow_mode; /* ClipByChildren, IncludeInferiors */
 Bool graphics_exposures; /* boolean, should exposures be generated */
 int clip_x_origin; /* origin for clipping */
 int clip_y_origin;
 Pixmap clip_mask; /* bitmap clipping; other calls for rects */
 int dash_offset; /* patterned/dashed line information */
 char dashes;
} XGCValues;



The function attributes of a GC are used when you update a section of
a drawable (the destination) with bits from somewhere else (the source).
The function in a GC defines how the new destination bits are to be
computed from the source bits and the old destination bits.
 GXcopy is typically the most useful because it will work on a color display,
but special applications may use other functions,
particularly in concert with particular planes of a color display.
The 16 GC functions, defined in
.hN X11/X.h ,
are:
 are listed in Table 5-1 along with the
the associated hexadecimal code
 and operation.
.CP T 1
Display Functions


 Function Name Value Operation
_
T{
 GXclear T} T{
0x0
T} T{
0
T}
T{
 GXand T} T{
0x1
T} T{
src AND dst
T}
T{
 GXandReverse T} T{
0x2
T} T{
src AND NOT dst
T}
T{
 GXcopy T} T{
0x3
T} T{
src
T}
T{
 GXandInverted T} T{
0x4
T} T{
(NOT src) AND dst
T}
T{
 GXnoop T} T{
0x5
T} T{
dst
T}
T{
 GXxor T} T{
0x6
T} T{
src XOR dst
T}
T{
 GXor T} T{
0x7
T} T{
src OR dst
T}
T{
 GXnor T} T{
0x8
T} T{
(NOT src) AND (NOT dst)
T}
T{
 GXequiv T} T{
0x9
T} T{
(NOT src) XOR dst
T}
T{
 GXinvert T} T{
0xa
T} T{
NOT dst
T}
T{
 GXorReverse T} T{
0xb
T} T{
src OR (NOT dst)
T}
T{
 GXcopyInverted T} T{
0xc
T} T{
NOT src
T}
T{
 GXorInverted T} T{
0xd
T} T{
(NOT src) OR dst
T}
T{
 GXnand T} T{
0xe
T} T{
(NOT src) OR (NOT dst)
T}
T{
 GXset T} T{
0xf
T} T{
1
T}
_
.TE


Many graphics operations depend on either pixel values or planes in a GC.
N "Pixel value" The planes attribute is of type long, and it specifies which planes of the
destination are to be modified, one bit per plane.
N "Plane" "mask" A monochrome display has only one plane and
will be the least significant bit of the word.
As planes are added to the display hardware, they will occupy more
significant bits in the plane mask.


In graphics operations, given a source and destination pixel,
the result is computed bitwise on corresponding bits of the pixels.
That is, a Boolean operation is performed in each bit plane.
The plane_mask restricts the operation to a subset of planes.
A macro constant
 AllPlanes can be used to refer to all planes of the screen simultaneously.
The result is computed by the following:


.EX
((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))



Range checking is not performed on the values for foreground,
background, or plane_mask.
They are simply truncated to the appropriate
number of bits.
The line-width is measured in pixels and either can be greater than or equal to
one (wide line) or can be the special value zero (thin line).


Wide lines are drawn centered on the path described by the graphics request.
Unless otherwise specified by the join-style or cap-style,
the bounding box of a wide line with endpoints [x1, y1], [x2, y2] and
width w is a rectangle with vertices at the following real coordinates:


.EX
[x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
[x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]



Here sn is the sine of the angle of the line,
and cs is the cosine of the angle of the line.
A pixel is part of the line and so is drawn
if the center of the pixel is fully inside the bounding box
(which is viewed as having infinitely thin edges).
If the center of the pixel is exactly on the bounding box,
it is part of the line if and only if the interior is immediately to its right
(x increasing direction).
Pixels with centers on a horizontal edge are a special case and are part of
the line if and only if the interior or the boundary is immediately below
(y increasing direction) and the interior or the boundary is immediately
to the right (x increasing direction).


Thin lines (zero line-width) are one-pixel-wide lines drawn using an
unspecified, device-dependent algorithm.
There are only two constraints on this algorithm.

 1. 5
If a line is drawn unclipped from [x1,y1] to [x2,y2] and
if another line is drawn unclipped from [x1+dx,y1+dy] to [x2+dx,y2+dy],
a point [x,y] is touched by drawing the first line
if and only if the point [x+dx,y+dy] is touched by drawing the second line.

 2. 5
The effective set of points comprising a line cannot be affected by clipping.
That is, a point is touched in a clipped line if and only if the point
lies inside the clipping region and the point would be touched
by the line when drawn unclipped.


A wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels
as a wide line drawn from [x2,y2] to [x1,y1], not counting cap-style
and join-style.
It is recommended that this property be true for thin lines,
but this is not required.
A line-width of zero may differ from a line-width of one in which pixels are
drawn.
This permits the use of many manufacturers' line drawing hardware,
which may run many times faster than the more precisely specified
wide lines.


In general,
drawing a thin line will be faster than drawing a wide line of width one.
However, because of their different drawing algorithms,
thin lines may not mix well aesthetically with wide lines.
If it is desirable to obtain precise and uniform results across all displays,
a client should always use a line-width of one rather than a line-width of zero.


The line-style defines which sections of a line are drawn:



 LineSolid T} T{
The full path of the line is drawn.
T}
T{
 LineDoubleDash T} T{
The full path of the line is drawn,
but the even dashes are filled differently
from the odd dashes (see fill-style) with
 CapButt style used where even and odd dashes meet.
T}
T{
 LineOnOffDash T} T{
Only the even dashes are drawn,
and cap-style applies to
all internal ends of the individual dashes,
except
 CapNotLast is treated as
 CapButt . T}
.TE


The cap-style defines how the endpoints of a path are drawn:
N "Graphics context" "path" 


 CapNotLast T} T{
This is equivalent to
 CapButt except that for a line-width of zero the final endpoint is not drawn.
T}
T{
 CapButt T} T{
The line is square at the endpoint (perpendicular to the slope of the line)
with no projection beyond.
T}
T{
 CapRound T} T{
The line has a circular arc with the diameter equal to the line-width,
centered on the endpoint.
(This is equivalent to
 CapButt for line-width of zero).
T}
T{
 CapProjecting T} T{
The line is square at the end, but the path continues beyond the endpoint
for a distance equal to half the line-width.
(This is equivalent to
 CapButt for line-width of zero).
T}
.TE


The join-style defines how corners are drawn for wide lines:



 JoinMiter T} T{
The outer edges of two lines extend to meet at an angle.
However, if the angle is less than 11 degrees,
then a
 JoinBevel join-style is used instead.
T}
T{
 JoinRound T} T{
The corner is a circular arc with the diameter equal to the line-width,
centered on the joinpoint.
T}
T{
 JoinBevel T} T{
The corner has
 CapButt endpoint styles with the triangular notch filled.
T}
.TE


For a line with coincident endpoints (x1=x2, y1=y2),
when the cap-style is applied to both endpoints,
the semantics depends on the line-width and the cap-style:



 CapNotLast T} T{
thin
T} T{
The results are device dependent,
but the desired effect is that nothing is drawn.
T}
T{
 CapButt T} T{
thin
T} T{
The results are device dependent,
but the desired effect is that a single pixel is drawn.
T}
T{
 CapRound T} T{
thin
T} T{
The results are the same as for
 CapButt /thin. T}
T{
 CapProjecting T} T{
thin
T} T{
The results are the same as for
 CapButt /thin. T}
T{
 CapButt T} T{
wide
T} T{
Nothing is drawn.
T}
T{
 CapRound T} T{
wide
T} T{
The closed path is a circle, centered at the endpoint, and
with the diameter equal to the line-width.
T}
T{
 CapProjecting T} T{
wide
T} T{
The closed path is a square, aligned with the coordinate axes, centered at the
endpoint, and with the sides equal to the line-width.
T}
.TE


For a line with coincident endpoints (x1=x2, y1=y2),
when the join-style is applied at one or both endpoints,
the effect is as if the line was removed from the overall path.
However, if the total path consists of or is reduced to a single point joined
with itself, the effect is the same as when the cap-style is applied at both
endpoints.


The tile/stipple represents an infinite two-dimensional plane,
with the tile/stipple replicated in all dimensions.
When that plane is superimposed on the drawable
for use in a graphics operation, the upper-left corner
of some instance of the tile/stipple is at the coordinates within
the drawable specified by the tile/stipple origin.
The tile/stipple and clip origins are interpreted relative to the
origin of whatever destination drawable is specified in a graphics
request.
The tile pixmap must have the same root and depth as the GC,
or a
 BadMatch error results.
The stipple pixmap must have depth one and must have the same root as the
GC, or a
 BadMatch error results.
For stipple operations where the fill-style is
 FillStippled but not
 FillOpaqueStippled , the stipple pattern is tiled in a
single plane and acts as an additional clip mask to be ANDed with the clip-mask.
Although some sizes may be faster to use than others,
any size pixmap can be used for tiling or stippling.


The fill-style defines the contents of the source for line, text, and
fill requests.
For all text and fill requests (for example,
 XDrawText ,  XDrawText16 ,  XFillRectangle ,  XFillPolygon , and
 XFillArc ); for line requests
with line-style
 LineSolid (for example,
 XDrawLine ,  XDrawSegments ,  XDrawRectangle ,  XDrawArc ); and for the even dashes for line requests with line-style
 LineOnOffDash or
 LineDoubleDash , the following apply:



 FillSolid T} T{
Foreground
T}
T{
 FillTiled T} T{
Tile
T}
T{
 FillOpaqueStippled T} T{
A tile with the same width and height as stipple,
but with background everywhere stipple has a zero
and with foreground everywhere stipple has a one
T}
T{
 FillStippled T} T{
Foreground masked by stipple
T}
.TE


When drawing lines with line-style
 LineDoubleDash , the odd dashes are controlled by the fill-style in the following manner:



 FillSolid T} T{
Background
T}
T{
 FillTiled T} T{
Same as for even dashes
T}
T{
 FillOpaqueStippled T} T{
Same as for even dashes
T}
T{
 FillStippled T} T{
Background masked by stipple
T}
.TE


Storing a pixmap in a GC might or might not result in a copy
being made.
If the pixmap is later used as the destination for a graphics request,
the change might or might not be reflected in the GC.
If the pixmap is used simultaneously in a graphics request both as
a destination and as a tile or stipple,
the results are undefined.


For optimum performance,
you should draw as much as possible with the same GC
(without changing its components).
The costs of changing GC components relative to using different GCs
depend on the display hardware and the server implementation.
It is quite likely that some amount of GC information will be
cached in display hardware and that such hardware can only cache a small number
of GCs.


The dashes value is actually a simplified form of the
more general patterns that can be set with
 XSetDashes . Specifying a
value of N is equivalent to specifying the two-element list [N, N] in
 XSetDashes . The value must be nonzero,
or a
 BadValue error results.


The clip-mask restricts writes to the destination drawable.
If the clip-mask is set to a pixmap,
it must have depth one and have the same root as the GC,
or a
 BadMatch error results.
If clip-mask is set to
 None , the pixels are always drawn regardless of the clip origin.
The clip-mask also can be set by calling the
 XSetClipRectangles or
 XSetRegion functions.
Only pixels where the clip-mask has a bit set to 1 are drawn.
Pixels are not drawn outside the area covered by the clip-mask
or where the clip-mask has a bit set to 0.
The clip-mask affects all graphics requests.
The clip-mask does not clip sources.
The clip-mask origin is interpreted relative to the origin of whatever
destination drawable is specified in a graphics request.


You can set the subwindow-mode to
 ClipByChildren or
 IncludeInferiors . For
 ClipByChildren , both source and destination windows are
additionally clipped by all viewable
 InputOutput children.
For
 IncludeInferiors , neither source nor destination window is clipped by inferiors.
This will result in including subwindow contents in the source
and drawing through subwindow boundaries of the destination.
The use of
 IncludeInferiors on a window of one depth with mapped
inferiors of differing depth is not illegal, but the semantics are
undefined by the core protocol.


The fill-rule defines what pixels are inside (drawn) for
paths given in
 XFillPolygon requests and can be set to
 EvenOddRule or
 WindingRule . For
 EvenOddRule , a point is inside if
an infinite ray with the point as origin crosses the path an odd number
of times.
For
 WindingRule , a point is inside if an infinite ray with the
point as origin crosses an unequal number of clockwise and
counterclockwise directed path segments.
A clockwise directed path segment is one that crosses the ray from left to
right as observed from the point.
A counterclockwise segment is one that crosses the ray from right to left
as observed from the point.
The case where a directed line segment is coincident with the ray is
uninteresting because you can simply choose a different ray that is not
coincident with a segment.


For both
 EvenOddRule and
 WindingRule , a point is infinitely small,
and the path is an infinitely thin line.
A pixel is inside if the center point of the pixel is inside
and the center point is not on the boundary.
If the center point is on the boundary,
the pixel is inside if and only if the polygon interior is immediately to
its right (x increasing direction).
Pixels with centers on a horizontal edge are a special case
and are inside if and only if the polygon interior is immediately below
(y increasing direction).


The arc-mode controls filling in the
 XFillArcs function and can be set to
 ArcPieSlice or
 ArcChord . For
 ArcPieSlice , the arcs are pie-slice filled.
For
 ArcChord , the arcs are chord filled.


The graphics-exposure flag controls
 GraphicsExpose event generation
for
 XCopyArea and
 XCopyPlane requests (and any similar requests defined by extensions).

 DIAGNOSTICS
 1i
 BadAlloc The server failed to allocate the requested resource or server memory.

 1i
 BadDrawable A value for a Drawable argument does not name a defined Window or Pixmap.

 1i
 BadFont A value for a Font or GContext argument does not name a defined Font.

 1i
 BadGC A value for a GContext argument does not name a defined GContext.

 1i
 BadMatch An
 InputOnly window is used as a Drawable.

 1i
 BadMatch Some argument or pair of arguments has the correct type and range but fails
to match in some other way required by the request.

 1i
 BadPixmap A value for a Pixmap argument does not name a defined Pixmap.

 1i
 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 ALSO"
AllPlanes(__libmansuffix__),
XCopyArea(__libmansuffix__),
XCreateRegion(__libmansuffix__),
XDrawArc(__libmansuffix__),
XDrawLine(__libmansuffix__),
XDrawRectangle(__libmansuffix__),
XDrawText(__libmansuffix__),
XFillRectangle(__libmansuffix__),
XQueryBestSize(__libmansuffix__),
XSetArcMode(__libmansuffix__),
XSetClipOrigin(__libmansuffix__),
XSetFillStyle(__libmansuffix__),
XSetFont(__libmansuffix__),
XSetLineAttributes(__libmansuffix__),
XSetState(__libmansuffix__),
XSetTile(__libmansuffix__)


\*(xL