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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 inclu-
		 sive 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.

       LineOnOffDash   Only the	even dashes are	drawn, and cap-style
		       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).
       CapProjecting   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).

       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.
       CapProjecting   thin    The results are the same	as for Cap-
			       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.
       CapProjecting   wide    The closed path is a square, aligned
			       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
       FillOpaqueStippled   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
       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
       FillOpaqueStippled   Same as for	even dashes
       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	1.6.5			  XCreateGC(3)

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

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