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XCreateGC(3)			XLIB FUNCTIONS			  XCreateGC(3)

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, XGCVal-
	      ues *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	 Specifies the drawable.

       dest	 Specifies the destination GC.

       display	 Specifies the connection to the X server.

       gc	 Specifies the GC.

       src	 Specifies the components of the source	GC.

       valuemask 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	 Specifies any values as specified by the valuemask.

       values_return
		 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,  Bad-
       Pixmap, 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	speci-
       fies 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 re-
       quest 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 (GCFunction, GCPlaneMask, GCForeground, GCBackground, GCLineWidth,
       GCLineStyle,  GCCapStyle, GCJoinStyle, GCFillStyle, GCFillRule, GCTile,
       GCStipple, GCTileStipXOrigin, GCTileStipYOrigin,	 GCFont,  GCSubwindow-
       Mode,  GCGraphicsExposures, GCClipXOrigin, GCClipYOrigin, GCDashOffset,
       or GCArcMode) and no error occurs, XGetGCValues sets the	requested com-
       ponents	in  values_return and returns a	nonzero	status.	 Otherwise, it
       returns a zero status.  Note that the clip-mask and  dash-list  (repre-
       sented by the GCClipMask	and GCDashList bits, respectively, in the val-
       uemask) 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 asso-
       ciated storage.

       XFreeGC can generate a BadGC error.

STRUCTURES
       The XGCValues structure contains:

       /* GC attribute value mask bits */

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

       /* 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, de-
       fined in	X11/X.h, are:

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

       Many graphics operations	depend on either pixel values or planes	 in  a
       GC.   The  planes  attribute  is	 of  type long,	and it specifies which
       planes of the destination are to	be modified, one  bit  per  plane.   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 re-
       sult is computed	bitwise	on corresponding bits of the pixels.  That is,
       a Boolean operation is performed	in each	bit plane.  The	plane_mask re-
       stricts the  operation  to  a  subset  of  planes.   A  macro  constant
       AllPlanes  can  be used to refer	to all planes of the screen simultane-
       ously.  The result is computed by the following:

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

       Range checking is not performed on the  values  for  foreground,	 back-
       ground,	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 re-
       quest.	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:

       [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 be-
       low  (y increasing direction) and the interior or the boundary is imme-
       diately 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 con-
       straints	on this	algorithm.

       1.   If a line is drawn unclipped from [x1,y1] to [x2,y2]  and  if  an-
	    other 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.   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    The	full path of the line is drawn.
       LineDou-	    The	full path of the line is drawn,	 but  the
       bleDash	    even  dashes  are filled differently from the
		    odd	 dashes	 (see  fill-style)  with  CapButt
		    style used where even and odd dashes meet.

       LineOnOff-   Only the even dashes are drawn, and	cap-style
       Dash	    applies  to	all internal ends of the individ-
		    ual	dashes,	except CapNotLast is  treated  as
		    CapButt.

       The cap-style defines how the endpoints of a path are drawn:

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

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

       JoinMiter    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.
       JoinRound    The	corner is a circular arc with the  diame-
		    ter	 equal to the line-width, centered on the
		    joinpoint.
       JoinBevel    The	corner has CapButt endpoint  styles  with
		    the	triangular notch filled.

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

       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 superim-
       posed 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 op-
       erations	where the fill-style is	FillStippled but  not  FillOpaqueStip-
       pled, the stipple pattern is tiled in a single plane and	acts as	an ad-
       ditional	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  re-
       quests  with  line-style	 LineSolid  (for example, XDrawLine, XDrawSeg-
       ments, XDrawRectangle, XDrawArc); and for the even dashes for line  re-
       quests  with  line-style	LineOnOffDash or LineDoubleDash, the following
       apply:

       FillSolid	 Foreground
       FillTiled	 Tile
       FillOpaqueStip-	 A tile	with the same width and	height as
       pled		 stipple, but with background  everywhere
			 stipple  has  a zero and with foreground
			 everywhere stipple has	a one
       FillStippled	 Foreground masked by stipple

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

       FillSolid	 Background
       FillTiled	 Same as for even dashes
       FillOpaqueStip-	 Same as for even dashes
       pled
       FillStippled	 Background masked by stipple

       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 destina-
       tion 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	 hard-
       ware  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 pat-
       terns 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  XSetRe-
       gion 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 addition-
       ally clipped by all viewable InputOutput	children.  For	IncludeInferi-
       ors,  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 dif-
       fering  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 seg-
       ments.  A clockwise directed path segment is one	that crosses  the  ray
       from left to right as observed from the point.  A counterclockwise seg-
       ment 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	bound-
       ary.  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 in-
       creasing	direction).  Pixels with centers on a horizontal  edge	are  a
       special	case and are inside if and only	if the polygon interior	is im-
       mediately 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
       BadAlloc	 The server failed  to	allocate  the  requested  resource  or
		 server	memory.

       BadDrawable
		 A  value for a	Drawable argument does not name	a defined Win-
		 dow or	Pixmap.

       BadFont	 A value for a Font or GContext	argument does not name	a  de-
		 fined Font.

       BadGC	 A value for a GContext	argument does not name a defined GCon-
		 text.

       BadMatch	 An InputOnly window is	used as	a Drawable.

       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.

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

       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(3),  XCopyArea(3),  XCreateRegion(3),	 XDrawArc(3),	XDraw-
       Line(3),	    XDrawRectangle(3),	   XDrawText(3),    XFillRectangle(3),
       XQueryBestSize(3), XSetArcMode(3), XSetClipOrigin(3), XSetFillStyle(3),
       XSetFont(3), XSetLineAttributes(3), XSetState(3), XSetTile(3)
       Xlib - C	Language X Interface

X Version 11			 libX11	1.7.2			  XCreateGC(3)

NAME | SYNTAX | ARGUMENTS | DESCRIPTION | STRUCTURES | DIAGNOSTICS | SEE ALSO

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