1XCreateGC(3)                    XLIB FUNCTIONS                    XCreateGC(3)
2
3
4

NAME

6       XCreateGC,  XCopyGC, XChangeGC, XGetGCValues, XFreeGC, XGContextFromGC,
7       XGCValues - create or  free  graphics  contexts  and  graphics  context
8       structure
9

SYNTAX

11       GC  XCreateGC(Display  *display,  Drawable  d, unsigned long valuemask,
12              XGCValues *values);
13
14       int XCopyGC(Display *display,  GC  src,  unsigned  long  valuemask,  GC
15              dest);
16
17       int XChangeGC(Display *display, GC gc, unsigned long valuemask, XGCVal‐
18              ues *values);
19
20       Status XGetGCValues(Display *display, GC gc, unsigned  long  valuemask,
21              XGCValues *values_return);
22
23       int XFreeGC(Display *display, GC gc);
24
25       GContext XGContextFromGC(GC gc);
26

ARGUMENTS

28       d         Specifies the drawable.
29
30       dest      Specifies the destination GC.
31
32       display   Specifies the connection to the X server.
33
34       gc        Specifies the GC.
35
36       src       Specifies the components of the source GC.
37
38       valuemask Specifies  which  components in the GC are to be set, copied,
39                 changed, or returned.  This argument is the bitwise inclusive
40                 OR of zero or more of the valid GC component mask bits.
41
42       values    Specifies any values as specified by the valuemask.
43
44       values_return
45                 Returns the GC values in the specified XGCValues structure.
46

DESCRIPTION

48       The  XCreateGC  function  creates  a graphics context and returns a GC.
49       The GC can be used with any destination drawable having the  same  root
50       and  depth as the specified drawable.  Use with other drawables results
51       in a BadMatch error.
52
53       XCreateGC can generate BadAlloc, BadDrawable, BadFont,  BadMatch,  Bad‐
54       Pixmap, and BadValue errors.
55
56       The XCopyGC function copies the specified components from the source GC
57       to the destination GC.  The source and destination GCs  must  have  the
58       same root and depth, or a BadMatch error results.  The valuemask speci‐
59       fies which component to copy, as for XCreateGC.
60
61       XCopyGC can generate BadAlloc, BadGC, and BadMatch errors.
62
63       The XChangeGC function changes the components  specified  by  valuemask
64       for  the  specified  GC.  The values argument contains the values to be
65       set.  The values and  restrictions  are  the  same  as  for  XCreateGC.
66       Changing   the  clip-mask  overrides  any  previous  XSetClipRectangles
67       request on the context.  Changing the dash-offset  or  dash-list  over‐
68       rides  any  previous  XSetDashes  request on the context.  The order in
69       which components are verified and altered is server dependent.   If  an
70       error is generated, a subset of the components may have been altered.
71
72       XChangeGC  can  generate BadAlloc, BadFont, BadGC, BadMatch, BadPixmap,
73       and BadValue errors.
74
75       The XGetGCValues function returns the components specified by valuemask
76       for the specified GC.  If the valuemask contains a valid set of GC mask
77       bits GCPlaneMask, GCForeground, GCBackground, GCLineWidth, GCLineStyle,
78       GCCapStyle,  GCJoinStyle,  GCFillStyle,  GCFillRule, GCTile, GCStipple,
79       GCTileStipXOrigin, GCTileStipYOrigin, GCFont, GCSubwindowMode, GCGraph‐
80       icsExposures, GCClipXOrigin, GCCLipYOrigin, GCDashOffset, or GCArcMode)
81       and no error occurs, XGetGCValues sets the requested components in val‐
82       ues_return  and returns a nonzero status.  Otherwise, it returns a zero
83       status.  Note that the clip-mask  and  dash-list  (represented  by  the
84       GCClipMask  and GCDashList bits, respectively, in the valuemask) cannot
85       be requested.  Also note that an invalid resource ID (with one or  more
86       of  the  three  most  significant  bits  set to 1) will be returned for
87       GCFont, GCTile, and GCStipple if the component has never  been  explic‐
88       itly set by the client.
89
90       The XFreeGC function destroys the specified GC as well as all the asso‐
91       ciated storage.
92
93       XFreeGC can generate a BadGC error.
94

STRUCTURES

96       The XGCValues structure contains:
97
98       /* GC attribute value mask bits */
99
100       #define   GCFunction                  (1L<<0)
101       #define   GCPlaneMask                 (1L<<1)
102       #define   GCForeground                (1L<<2)
103       #define   GCBackground                (1L<<3)
104       #define   GCLineWidth                 (1L<<4)
105       #define   GCLineStyle                 (1L<<5)
106       #define   GCCapStyle                  (1L<<6)
107       #define   GCJoinStyle                 (1L<<7)
108       #define   GCFillStyle                 (1L<<8)
109       #define   GCFillRule                  (1L<<9)
110       #define   GCTile                      (1L<<10)
111       #define   GCStipple                   (1L<<11)
112       #define   GCTileStipXOrigin           (1L<<12)
113       #define   GCTileStipYOrigin           (1L<<13)
114       #define   GCFont                      (1L<<14)
115       #define   GCSubwindowMode             (1L<<15)
116       #define   GCGraphicsExposures         (1L<<16)
117       #define   GCClipXOrigin               (1L<<17)
118       #define   GCClipYOrigin               (1L<<18)
119       #define   GCClipMask                  (1L<<19)
120       #define   GCDashOffset                (1L<<20)
121       #define   GCDashList                  (1L<<21)
122       #define   GCArcMode                   (1L<<22)
123
124       /* Values */
125
126       typedef struct {
127               int function;   /* logical operation */
128               unsigned long plane_mask;       /* plane mask */
129               unsigned long foreground;       /* foreground pixel */
130               unsigned long background;       /* background pixel */
131               int line_width; /* line width (in pixels) */
132               int line_style; /* LineSolid, LineOnOffDash, LineDoubleDash */
133               int cap_style;  /* CapNotLast, CapButt, CapRound, CapProjecting */
134               int join_style; /* JoinMiter, JoinRound, JoinBevel */
135               int fill_style; /* FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
136               int fill_rule;  /* EvenOddRule, WindingRule */
137               int arc_mode;   /* ArcChord, ArcPieSlice */
138               Pixmap tile;    /* tile pixmap for tiling operations */
139               Pixmap stipple; /* stipple 1 plane pixmap for stippling */
140               int ts_x_origin;        /* offset for tile or stipple operations */
141               int ts_y_origin;
142               Font font;      /* default text font for text operations */
143               int subwindow_mode;     /* ClipByChildren, IncludeInferiors */
144               Bool graphics_exposures;        /* boolean, should exposures be generated */
145               int clip_x_origin;      /* origin for clipping */
146               int clip_y_origin;
147               Pixmap clip_mask;       /* bitmap clipping; other calls for rects */
148               int dash_offset;        /* patterned/dashed line information */
149               char dashes;
150       } XGCValues;
151
152       The function attributes of a GC are used when you update a section of a
153       drawable (the destination) with bits from somewhere else (the  source).
154       The  function  in  a  GC defines how the new destination bits are to be
155       computed from the source bits and the old destination bits.  GXcopy  is
156       typically  the most useful because it will work on a color display, but
157       special applications may use other functions, particularly  in  concert
158       with  particular  planes  of  a  color  display.   The 16 GC functions,
159       defined in are:
160
161       ───────────────────────────────────────────────
162       Function Name     Value   Operation
163       ───────────────────────────────────────────────
164       GXclear            0x0    0
165       GXand              0x1    src AND dst
166       GXandReverse       0x2    src AND NOT dst
167       GXcopy             0x3    src
168       GXandInverted      0x4    (NOT src) AND dst
169       GXnoop             0x5    dst
170       GXxor              0x6    src XOR dst
171       GXor               0x7    src OR dst
172       GXnor              0x8    (NOT src)  AND  (NOT
173                                 dst)
174       GXequiv            0x9    (NOT src) XOR dst
175       GXinvert           0xa    NOT dst
176       GXorReverse        0xb    src OR (NOT dst)
177       GXcopyInverted     0xc    NOT src
178       GXorInverted       0xd    (NOT src) OR dst
179       GXnand             0xe    (NOT  src)  OR  (NOT
180                                 dst)
181       GXset              0xf    1
182       ───────────────────────────────────────────────
183
184       Many graphics operations depend on either pixel values or planes  in  a
185       GC.   The  planes  attribute  is  of  type long, and it specifies which
186       planes of the destination are to be modified, one  bit  per  plane.   A
187       monochrome display has only one plane and will be the least significant
188       bit of the word.  As planes are added to  the  display  hardware,  they
189       will occupy more significant bits in the plane mask.
190
191       In  graphics  operations,  given  a  source  and destination pixel, the
192       result is computed bitwise on corresponding bits of the  pixels.   That
193       is, a Boolean operation is performed in each bit plane.  The plane_mask
194       restricts the operation to  a  subset  of  planes.   A  macro  constant
195       AllPlanes  can  be used to refer to all planes of the screen simultane‐
196       ously.  The result is computed by the following:
197
198       ((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))
199
200       Range checking is not performed on the  values  for  foreground,  back‐
201       ground,  or  plane_mask.   They are simply truncated to the appropriate
202       number of bits.  The line-width is measured in pixels and either can be
203       greater  than  or  equal to one (wide line) or can be the special value
204       zero (thin line).
205
206       Wide lines are drawn centered on the path  described  by  the  graphics
207       request.   Unless  otherwise  specified by the join-style or cap-style,
208       the bounding box of a wide line with endpoints [x1, y1], [x2,  y2]  and
209       width w is a rectangle with vertices at the following real coordinates:
210
211       [x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
212       [x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]
213
214       Here  sn  is the sine of the angle of the line, and cs is the cosine of
215       the angle of the line.  A pixel is part of the line and so is drawn  if
216       the  center  of  the  pixel  is fully inside the bounding box (which is
217       viewed as having infinitely thin edges).  If the center of the pixel is
218       exactly  on the bounding box, it is part of the line if and only if the
219       interior is immediately to its right (x increasing direction).   Pixels
220       with  centers  on  a horizontal edge are a special case and are part of
221       the line if and only if the interior or  the  boundary  is  immediately
222       below  (y  increasing  direction)  and  the interior or the boundary is
223       immediately to the right (x increasing direction).
224
225       Thin lines (zero line-width) are one-pixel-wide lines  drawn  using  an
226       unspecified,  device-dependent  algorithm.   There  are  only  two con‐
227       straints on this algorithm.
228
229       1.   If a line is drawn  unclipped  from  [x1,y1]  to  [x2,y2]  and  if
230            another   line   is   drawn   unclipped   from   [x1+dx,y1+dy]  to
231            [x2+dx,y2+dy], a point [x,y] is touched by drawing the first  line
232            if  and  only  if  the point [x+dx,y+dy] is touched by drawing the
233            second line.
234
235       2.   The effective set of points comprising a line cannot  be  affected
236            by clipping.  That is, a point is touched in a clipped line if and
237            only if the point lies inside the clipping region  and  the  point
238            would be touched by the line when drawn unclipped.
239
240       A  wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels
241       as a wide line drawn from [x2,y2] to [x1,y1],  not  counting  cap-style
242       and  join-style.  It is recommended that this property be true for thin
243       lines, but this is not required.  A line-width of zero may differ  from
244       a line-width of one in which pixels are drawn.  This permits the use of
245       many manufacturers' line drawing hardware, which  may  run  many  times
246       faster than the more precisely specified wide lines.
247
248       In general, drawing a thin line will be faster than drawing a wide line
249       of width one.  However, because of their different drawing  algorithms,
250       thin  lines  may  not mix well aesthetically with wide lines.  If it is
251       desirable to obtain precise and uniform results across all displays,  a
252       client  should  always use a line-width of one rather than a line-width
253       of zero.
254
255       The line-style defines which sections of a line are drawn:
256
257       LineSolid    The full path of the line is drawn.
258       LineDou‐     The  full  path of the line is drawn, but the
259       bleDash      even dashes are filled differently  from  the
260                    odd  dashes  (see  fill-style)  with  CapButt
261                    style used where even and odd dashes meet.
262
263
264
265       LineOnOff‐   Only the even dashes are drawn, and cap-style
266       Dash         applies to all internal ends of the  individ‐
267                    ual  dashes,  except CapNotLast is treated as
268                    CapButt.
269
270       The cap-style defines how the endpoints of a path are drawn:
271
272       CapNotLast   This is equivalent to CapButt except that for
273                    a  line-width  of  zero the final endpoint is
274                    not drawn.
275       CapButt      The line is square at the  endpoint  (perpen‐
276                    dicular  to  the  slope  of the line) with no
277                    projection beyond.
278       CapRound     The line has a circular arc with the diameter
279                    equal to the line-width, centered on the end‐
280                    point.  (This is equivalent  to  CapButt  for
281                    line-width of zero).
282       CapPro‐      The line is square at the end, but  the  path
283       jecting      continues  beyond the endpoint for a distance
284                    equal  to  half  the  line-width.   (This  is
285                    equivalent   to  CapButt  for  line-width  of
286                    zero).
287
288       The join-style defines how corners are drawn for wide lines:
289
290       JoinMiter    The outer edges of two lines extend  to  meet
291                    at  an  angle.  However, if the angle is less
292                    than 11 degrees, then a JoinBevel  join-style
293                    is used instead.
294       JoinRound    The  corner is a circular arc with the diame‐
295                    ter equal to the line-width, centered on  the
296                    joinpoint.
297       JoinBevel    The  corner  has CapButt endpoint styles with
298                    the triangular notch filled.
299
300       For a line with coincident endpoints (x1=x2, y1=y2), when the cap-style
301       is  applied  to both endpoints, the semantics depends on the line-width
302       and the cap-style:
303
304       CapNotLast   thin    The results are  device  dependent,  but
305                            the  desired  effect  is that nothing is
306                            drawn.
307       CapButt      thin    The results are  device  dependent,  but
308                            the  desired  effect  is  that  a single
309                            pixel is drawn.
310       CapRound     thin    The results are the  same  as  for  Cap‐
311                            Butt/thin.
312       CapPro‐      thin    The results are the  same  as  for  Cap‐
313       jecting              Butt/thin.
314       CapButt      wide    Nothing is drawn.
315       CapRound     wide    The closed path is a circle, centered at
316                            the  endpoint,  and  with  the  diameter
317                            equal to the line-width.
318       CapPro‐      wide    The closed path  is  a  square,  aligned
319       jecting              with  the  coordinate  axes, centered at
320                            the endpoint, and with the  sides  equal
321                            to the line-width.
322
323       For  a  line  with  coincident endpoints (x1=x2, y1=y2), when the join-
324       style is applied at one or both endpoints, the effect is as if the line
325       was removed from the overall path.  However, if the total path consists
326       of or is reduced to a single point joined with itself,  the  effect  is
327       the same as when the cap-style is applied at both endpoints.
328
329       The tile/stipple represents an infinite two-dimensional plane, with the
330       tile/stipple replicated in all dimensions.  When that plane is superim‐
331       posed  on  the drawable for use in a graphics operation, the upper-left
332       corner of some instance of  the  tile/stipple  is  at  the  coordinates
333       within   the  drawable  specified  by  the  tile/stipple  origin.   The
334       tile/stipple and clip origins are interpreted relative to the origin of
335       whatever  destination drawable is specified in a graphics request.  The
336       tile pixmap must have the same root and depth as the GC, or a  BadMatch
337       error  results.   The  stipple pixmap must have depth one and must have
338       the same root as the GC, or a  BadMatch  error  results.   For  stipple
339       operations where the fill-style is FillStippled but not FillOpaqueStip‐
340       pled, the stipple pattern is tiled in a single plane  and  acts  as  an
341       additional  clip  mask  to  be ANDed with the clip-mask.  Although some
342       sizes may be faster to use than others, any size pixmap can be used for
343       tiling or stippling.
344
345       The  fill-style  defines the contents of the source for line, text, and
346       fill requests.  For all text and fill requests (for example, XDrawText,
347       XDrawText16,  XFillRectangle,  XFillPolygon,  and  XFillArc);  for line
348       requests with line-style LineSolid (for example,  XDrawLine,  XDrawSeg‐
349       ments,  XDrawRectangle,  XDrawArc);  and  for  the even dashes for line
350       requests with line-style LineOnOffDash or LineDoubleDash, the following
351       apply:
352
353       FillSolid         Foreground
354       FillTiled         Tile
355       FillOpaqueStip‐   A tile with the same width and height as
356       pled              stipple,  but with background everywhere
357                         stipple has a zero and  with  foreground
358                         everywhere stipple has a one
359       FillStippled      Foreground masked by stipple
360
361       When  drawing  lines with line-style LineDoubleDash, the odd dashes are
362       controlled by the fill-style in the following manner:
363
364       FillSolid         Background
365       FillTiled         Same as for even dashes
366       FillOpaqueStip‐   Same as for even dashes
367       pled
368       FillStippled      Background masked by stipple
369
370       Storing  a  pixmap  in  a  GC might or might not result in a copy being
371       made.  If the pixmap is later used as the destination  for  a  graphics
372       request,  the change might or might not be reflected in the GC.  If the
373       pixmap is used simultaneously in a graphics request both as a  destina‐
374       tion and as a tile or stipple, the results are undefined.
375
376       For  optimum  performance, you should draw as much as possible with the
377       same GC (without changing its components).  The costs  of  changing  GC
378       components  relative to using different GCs depend on the display hard‐
379       ware and the server implementation.   It  is  quite  likely  that  some
380       amount  of  GC  information will be cached in display hardware and that
381       such hardware can only cache a small number of GCs.
382
383       The dashes value is actually a simplified form of the more general pat‐
384       terns  that  can  be  set  with XSetDashes.  Specifying a value of N is
385       equivalent to specifying the two-element list  [N,  N]  in  XSetDashes.
386       The value must be nonzero, or a BadValue error results.
387
388       The  clip-mask  restricts  writes  to the destination drawable.  If the
389       clip-mask is set to a pixmap, it must have depth one and have the  same
390       root  as  the  GC, or a BadMatch error results.  If clip-mask is set to
391       None, the pixels are always drawn regardless of the clip  origin.   The
392       clip-mask  also can be set by calling the XSetClipRectangles or XSetRe‐
393       gion functions.  Only pixels where the clip-mask has a bit set to 1 are
394       drawn.   Pixels are not drawn outside the area covered by the clip-mask
395       or where the clip-mask has a bit set to 0.  The clip-mask  affects  all
396       graphics requests.  The clip-mask does not clip sources.  The clip-mask
397       origin is interpreted relative to the origin  of  whatever  destination
398       drawable is specified in a graphics request.
399
400       You  can  set the subwindow-mode to ClipByChildren or IncludeInferiors.
401       For ClipByChildren, both source and destination windows  are  addition‐
402       ally  clipped by all viewable InputOutput children.  For IncludeInferi‐
403       ors, neither source nor destination window  is  clipped  by  inferiors.
404       This  will  result  in  including  subwindow contents in the source and
405       drawing through subwindow boundaries of the destination.   The  use  of
406       IncludeInferiors on a window of one depth with mapped inferiors of dif‐
407       fering depth is not illegal, but the semantics  are  undefined  by  the
408       core protocol.
409
410       The fill-rule defines what pixels are inside (drawn) for paths given in
411       XFillPolygon requests and can be set  to  EvenOddRule  or  WindingRule.
412       For EvenOddRule, a point is inside if an infinite ray with the point as
413       origin crosses the path an odd number of  times.   For  WindingRule,  a
414       point  is inside if an infinite ray with the point as origin crosses an
415       unequal number of clockwise and  counterclockwise  directed  path  seg‐
416       ments.   A  clockwise directed path segment is one that crosses the ray
417       from left to right as observed from the point.  A counterclockwise seg‐
418       ment  is  one  that crosses the ray from right to left as observed from
419       the point.  The case where a directed line segment is  coincident  with
420       the  ray is uninteresting because you can simply choose a different ray
421       that is not coincident with a segment.
422
423       For both EvenOddRule and WindingRule, a point is infinitely small,  and
424       the  path  is an infinitely thin line.  A pixel is inside if the center
425       point of the pixel is inside and the center point is not on the  bound‐
426       ary.   If  the  center point is on the boundary, the pixel is inside if
427       and only if the  polygon  interior  is  immediately  to  its  right  (x
428       increasing  direction).  Pixels with centers on a horizontal edge are a
429       special case and are inside if and only  if  the  polygon  interior  is
430       immediately below (y increasing direction).
431
432       The  arc-mode controls filling in the XFillArcs function and can be set
433       to ArcPieSlice or ArcChord.  For ArcPieSlice, the  arcs  are  pie-slice
434       filled.  For ArcChord, the arcs are chord filled.
435
436       The graphics-exposure flag controls GraphicsExpose event generation for
437       XCopyArea and XCopyPlane requests (and any similar requests defined  by
438       extensions).
439

DIAGNOSTICS

441       BadAlloc  The  server  failed  to  allocate  the  requested resource or
442                 server memory.
443
444       BadDrawable
445                 A value for a Drawable argument does not name a defined  Win‐
446                 dow or Pixmap.
447
448       BadFont   A  value  for  a  Font  or  GContext argument does not name a
449                 defined Font.
450
451       BadGC     A value for a GContext argument does not name a defined GCon‐
452                 text.
453
454       BadMatch  An InputOnly window is used as a Drawable.
455
456       BadMatch  Some  argument  or pair of arguments has the correct type and
457                 range but fails to match in some other way  required  by  the
458                 request.
459
460       BadPixmap A value for a Pixmap argument does not name a defined Pixmap.
461
462       BadValue  Some numeric value falls outside the range of values accepted
463                 by the request.  Unless a specific range is specified for  an
464                 argument,  the  full  range defined by the argument's type is
465                 accepted.  Any argument defined as a set of alternatives  can
466                 generate this error.
467

SEE ALSO

469       AllPlanes(3),   XCopyArea(3),   XCreateRegion(3),  XDrawArc(3),  XDraw‐
470       Line(3),    XDrawRectangle(3),     XDrawText(3),     XFillRectangle(3),
471       XQueryBestSize(3), XSetArcMode(3), XSetClipOrigin(3), XSetFillStyle(3),
472       XSetFont(3), XSetLineAttributes(3), XSetState(3), XSetTile(3)
473       Xlib - C Language X Interface
474
475
476
477X Version 11                     libX11 1.6.9                     XCreateGC(3)
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