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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
       request on the context.  Changing the dash-offset  or  dash-list  over-
       rides  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  Fil-
       lOpaqueStippled*/
               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 opera-
       tions */
               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 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
       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 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
       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:

       [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 con-
       straints on this algorithm.

       1.   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.   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
       operations where the fill-style is FillStippled but not FillOpaqueStip-
       pled, 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,  XDrawSeg-
       ments,  XDrawRectangle,  XDrawArc);  and  for  the even dashes for line
       requests 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
       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

       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
                 defined 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 1.7.1                     XCreateGC(3)

xorg-libX11 1.7.1 - Generated Sat May 22 10:40:08 CDT 2021
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