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 re‐
67       quest on the context.  Changing the dash-offset or dash-list  overrides
68       any  previous  XSetDashes  request  on the context.  The order in which
69       components are verified and altered is server dependent.  If  an  error
70       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  GC‐
84       ClipMask and GCDashList bits, respectively, in the valuemask) cannot be
85       requested.  Also note that an invalid resource ID (with one or more  of
86       the  three most significant bits set to 1) will be returned for GCFont,
87       GCTile, and GCStipple if the component has never been explicitly set by
88       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, de‐
159       fined 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 re‐
192       sult is computed bitwise on corresponding bits of the pixels.  That is,
193       a Boolean operation is performed in each bit plane.  The plane_mask re‐
194       stricts 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 re‐
207       quest.   Unless otherwise specified by the join-style or cap-style, the
208       bounding box of a wide line with endpoints [x1, y1], [x2, y2] and width
209       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 be‐
222       low  (y increasing direction) and the interior or the boundary is imme‐
223       diately 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  an‐
230            other line is drawn unclipped from [x1+dx,y1+dy] to [x2+dx,y2+dy],
231            a point [x,y] is touched by drawing the first line if and only  if
232            the point [x+dx,y+dy] is touched by drawing the second line.
233
234       2.   The  effective  set of points comprising a line cannot be affected
235            by clipping.  That is, a point is touched in a clipped line if and
236            only  if  the  point lies inside the clipping region and the point
237            would be touched by the line when drawn unclipped.
238
239       A wide line drawn from [x1,y1] to [x2,y2] always draws the same  pixels
240       as  a  wide  line drawn from [x2,y2] to [x1,y1], not counting cap-style
241       and join-style.  It is recommended that this property be true for  thin
242       lines,  but this is not required.  A line-width of zero may differ from
243       a line-width of one in which pixels are drawn.  This permits the use of
244       many  manufacturers'  line  drawing  hardware, which may run many times
245       faster than the more precisely specified wide lines.
246
247       In general, drawing a thin line will be faster than drawing a wide line
248       of  width one.  However, because of their different drawing algorithms,
249       thin lines may not mix well aesthetically with wide lines.   If  it  is
250       desirable  to obtain precise and uniform results across all displays, a
251       client should always use a line-width of one rather than  a  line-width
252       of zero.
253
254       The line-style defines which sections of a line are drawn:
255
256       LineSolid    The full path of the line is drawn.
257       LineDou‐     The full path of the line is drawn,  but  the
258       bleDash      even  dashes  are filled differently from the
259                    odd  dashes  (see  fill-style)  with  CapButt
260                    style used where even and odd dashes meet.
261
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 op‐
339       erations where the fill-style is FillStippled but  not  FillOpaqueStip‐
340       pled, the stipple pattern is tiled in a single plane and acts as an ad‐
341       ditional clip mask to be ANDed with the clip-mask.  Although some sizes
342       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  re‐
348       quests  with  line-style  LineSolid  (for example, XDrawLine, XDrawSeg‐
349       ments, XDrawRectangle, XDrawArc); and for the even dashes for line  re‐
350       quests  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 in‐
428       creasing direction).  Pixels with centers on a horizontal  edge  are  a
429       special  case and are inside if and only if the polygon interior is im‐
430       mediately 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  de‐
449                 fined 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 1.7.0                     XCreateGC(3)
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