1XCreateGC(3) XLIB FUNCTIONS XCreateGC(3)
2
6 XCreateGC, XCopyGC, XChangeGC, XGetGCValues, XFreeGC, XGContextFromGC,
7 XGCValues - create or free graphics contexts and graphics context
8 structure
9
11 GC XCreateGC(Display *display, Drawable d, unsigned long valuemask,
12 XGCValues *values);
13 int XCopyGC(Display *display, GC src, unsigned long valuemask, GC
15 dest);
16 int XChangeGC(Display *display, GC gc, unsigned long valuemask, XGCVal‐
18 ues *values);
19 Status XGetGCValues(Display *display, GC gc, unsigned long valuemask,
21 XGCValues *values_return);
22 int XFreeGC(Display *display, GC gc);
24 GContext XGContextFromGC(GC gc);
26
28 d Specifies the drawable.
29 dest Specifies the destination GC.
31 display Specifies the connection to the X server.
33 gc Specifies the GC.
35 src Specifies the components of the source GC.
37 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 values Specifies any values as specified by the valuemask.
43 values_return
45 Returns the GC values in the specified XGCValues structure.
46
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 XCreateGC can generate BadAlloc, BadDrawable, BadFont, BadMatch, Bad‐
54 Pixmap, and BadValue errors.
55 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 XCopyGC can generate BadAlloc, BadGC, and BadMatch errors.
62 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 XChangeGC can generate BadAlloc, BadFont, BadGC, BadMatch, BadPixmap,
73 and BadValue errors.
74 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 (GCFunction, GCPlaneMask, GCForeground, GCBackground, GCLineWidth,
78 GCLineStyle, GCCapStyle, GCJoinStyle, GCFillStyle, GCFillRule, GCTile,
79 GCStipple, GCTileStipXOrigin, GCTileStipYOrigin, GCFont, GCSubwindow‐
80 Mode, GCGraphicsExposures, GCClipXOrigin, GCClipYOrigin, GCDashOffset,
81 or GCArcMode) and no error occurs, XGetGCValues sets the requested com‐
82 ponents in values_return and returns a nonzero status. Otherwise, it
83 returns a zero status. Note that the clip-mask and dash-list (repre‐
84 sented by the GCClipMask and GCDashList bits, respectively, in the val‐
85 uemask) cannot be requested. Also note that an invalid resource ID
86 (with one or more of the three most significant bits set to 1) will be
87 returned for GCFont, GCTile, and GCStipple if the component has never
88 been explicitly set by the client.
89 The XFreeGC function destroys the specified GC as well as all the asso‐
91 ciated storage.
92 XFreeGC can generate a BadGC error.
94
96 The XGCValues structure contains:
97 /* GC attribute value mask bits */
99 #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 /* Values */
125 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 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 X11/X.h, are:
160 ───────────────────────────────────────────────
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 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 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 ((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))
199 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 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 [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 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 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 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 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 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 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 The line-style defines which sections of a line are drawn:
255 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 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 The cap-style defines how the endpoints of a path are drawn:
271 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 The join-style defines how corners are drawn for wide lines:
289 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 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 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 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 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 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 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 When drawing lines with line-style LineDoubleDash, the odd dashes are
362 controlled by the fill-style in the following manner:
363 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 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 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 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 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 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 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 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 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 The graphics-exposure flag controls GraphicsExpose event generation for
437 XCopyArea and XCopyPlane requests (and any similar requests defined by
438 extensions).
439
441 BadAlloc The server failed to allocate the requested resource or
442 server memory.
443 BadDrawable
445 A value for a Drawable argument does not name a defined Win‐
446 dow or Pixmap.
447 BadFont A value for a Font or GContext argument does not name a de‐
449 fined Font.
450 BadGC A value for a GContext argument does not name a defined GCon‐
452 text.
453 BadMatch An InputOnly window is used as a Drawable.
455 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 BadPixmap A value for a Pixmap argument does not name a defined Pixmap.
461 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
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
474X Version 11 libX11 1.7.3.1 XCreateGC(3)