1XCreateGC(3X11) XLIB FUNCTIONS XCreateGC(3X11)
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, GC dest, unsigned long value‐
15 mask);
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 inclu‐
40 sive 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
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 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 */
124 typedef struct {
126 int function; /∗ logical operation */
127 unsigned long plane_mask;/∗ plane mask */
128 unsigned long foreground;/∗ foreground pixel */
129 unsigned long background;/∗ background pixel */
130 int line_width; /∗ line width (in pixels) */
131 int line_style; /∗ LineSolid, LineOnOffDash, LineDoubleDash */
132 int cap_style; /∗ CapNotLast, CapButt, CapRound, CapProjecting */
133 int join_style; /∗ JoinMiter, JoinRound, JoinBevel */
134 int fill_style; /∗ FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
135 int fill_rule; /∗ EvenOddRule, WindingRule */
136 int arc_mode; /∗ ArcChord, ArcPieSlice */
137 Pixmap tile; /∗ tile pixmap for tiling operations */
138 Pixmap stipple; /∗ stipple 1 plane pixmap for stippling */
139 int ts_x_origin; /∗ offset for tile or stipple operations */
140 int ts_y_origin;
141 Font font; /∗ default text font for text operations */
142 int subwindow_mode; /∗ ClipByChildren, IncludeInferiors */
143 Bool graphics_exposures; /∗ boolean, should exposures be generated */
144 int clip_x_origin; /∗ origin for clipping */
145 int clip_y_origin;
146 Pixmap clip_mask; /∗ bitmap clipping; other calls for rects */
147 int dash_offset; /∗ patterned/dashed line information */
148 char dashes;
149 } XGCValues;
150 The function attributes of a GC are used when you update a section of a
152 drawable (the destination) with bits from somewhere else (the source).
153 The function in a GC defines how the new destination bits are to be
154 computed from the source bits and the old destination bits. GXcopy is
155 typically the most useful because it will work on a color display, but
156 special applications may use other functions, particularly in concert
157 with particular planes of a color display. The 16 GC functions,
158 defined in <X11/X.h>, are:
159 ───────────────────────────────────────────────
161 Function Name Value Operation
162 ───────────────────────────────────────────────
163 () ()
167 GXclear 0x0 0
171 GXand 0x1 src AND dst
172 GXandReverse 0x2 src AND NOT dst
173 GXcopy 0x3 src
174 GXandInverted 0x4 (NOT src) AND dst
175 GXnoop 0x5 dst
176 GXxor 0x6 src XOR dst
177 GXor 0x7 src OR dst
178 GXnor 0x8 (NOT src) AND (NOT
179 dst)
180 GXequiv 0x9 (NOT src) XOR dst
181 GXinvert 0xa NOT dst
182 GXorReverse 0xb src OR (NOT dst)
183 GXcopyInverted 0xc NOT src
184 GXorInverted 0xd (NOT src) OR dst
185 GXnand 0xe (NOT src) OR (NOT
186 dst)
187 GXset 0xf 1
188 ───────────────────────────────────────────────
189 Many graphics operations depend on either pixel values or planes in a
191 GC. The planes attribute is of type long, and it specifies which
192 planes of the destination are to be modified, one bit per plane. A
193 monochrome display has only one plane and will be the least significant
194 bit of the word. As planes are added to the display hardware, they
195 will occupy more significant bits in the plane mask.
196 In graphics operations, given a source and destination pixel, the
198 result is computed bitwise on corresponding bits of the pixels. That
199 is, a Boolean operation is performed in each bit plane. The plane_mask
200 restricts the operation to a subset of planes. A macro constant
201 AllPlanes can be used to refer to all planes of the screen simultane‐
202 ously. The result is computed by the following:
203 ((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))
205 Range checking is not performed on the values for foreground, back‐
207 ground, or plane_mask. They are simply truncated to the appropriate
208 number of bits. The line-width is measured in pixels and either can be
209 greater than or equal to one (wide line) or can be the special value
210 zero (thin line).
211 Wide lines are drawn centered on the path described by the graphics
213 request. Unless otherwise specified by the join-style or cap-style,
214 the bounding box of a wide line with endpoints [x1, y1], [x2, y2] and
215 width w is a rectangle with vertices at the following real coordinates:
216 [x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
218 [x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]
219 Here sn is the sine of the angle of the line, and cs is the cosine of
221 the angle of the line. A pixel is part of the line and so is drawn if
222 the center of the pixel is fully inside the bounding box (which is
223 viewed as having infinitely thin edges). If the center of the pixel is
224 exactly on the bounding box, it is part of the line if and only if the
225 interior is immediately to its right (x increasing direction). Pixels
226 with centers on a horizontal edge are a special case and are part of
227 the line if and only if the interior or the boundary is immediately
228 below (y increasing direction) and the interior or the boundary is
229 immediately to the right (x increasing direction).
230 Thin lines (zero line-width) are one-pixel-wide lines drawn using an
232 unspecified, device-dependent algorithm. There are only two con‐
233 straints on this algorithm.
234 1. If a line is drawn unclipped from [x1,y1] to [x2,y2] and if
236 another line is drawn unclipped from [x1+dx,y1+dy] to
237 [x2+dx,y2+dy], a point [x,y] is touched by drawing the first line
238 if and only if the point [x+dx,y+dy] is touched by drawing the
239 second line.
240 2. The effective set of points comprising a line cannot be affected
242 by clipping. That is, a point is touched in a clipped line if and
243 only if the point lies inside the clipping region and the point
244 would be touched by the line when drawn unclipped.
245 A wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels
247 as a wide line drawn from [x2,y2] to [x1,y1], not counting cap-style
248 and join-style. It is recommended that this property be true for thin
249 lines, but this is not required. A line-width of zero may differ from
250 a line-width of one in which pixels are drawn. This permits the use of
251 many manufacturers' line drawing hardware, which may run many times
252 faster than the more precisely specified wide lines.
253 In general, drawing a thin line will be faster than drawing a wide line
255 of width one. However, because of their different drawing algorithms,
256 thin lines may not mix well aesthetically with wide lines. If it is
257 desirable to obtain precise and uniform results across all displays, a
258 client should always use a line-width of one rather than a line-width
259 of zero.
260 The line-style defines which sections of a line are drawn:
262 LineSolid The full path of the line is drawn.
264 LineDou‐ The full path of the line is drawn, but the
266 bleDash even dashes are filled differently from the
267 odd dashes (see fill-style) with CapButt
268 style used where even and odd dashes meet.
269 LineOnOffDash Only the even dashes are drawn, and cap-style
270 applies to all internal ends of the individ‐
271 ual dashes, except CapNotLast is treated as
272 CapButt.
273 The cap-style defines how the endpoints of a path are drawn:
275 CapNotLast This is equivalent to CapButt except that for
277 a line-width of zero the final endpoint is
278 not drawn.
279 CapButt The line is square at the endpoint (perpen‐
280 dicular to the slope of the line) with no
281 projection beyond.
282 CapRound The line has a circular arc with the diameter
283 equal to the line-width, centered on the end‐
284 point. (This is equivalent to CapButt for
285 line-width of zero).
286 CapProjecting The line is square at the end, but the path
287 continues beyond the endpoint for a distance
288 equal to half the line-width. (This is
289 equivalent to CapButt for line-width of
290 zero).
291 The join-style defines how corners are drawn for wide lines:
293 JoinMiter The outer edges of two lines extend to meet
295 at an angle. However, if the angle is less
296 than 11 degrees, then a JoinBevel join-style
297 is used instead.
298 JoinRound The corner is a circular arc with the diame‐
299 ter equal to the line-width, centered on the
300 joinpoint.
301 JoinBevel The corner has CapButt endpoint styles with
302 the triangular notch filled.
303 For a line with coincident endpoints (x1=x2, y1=y2), when the cap-style
305 is applied to both endpoints, the semantics depends on the line-width
306 and the cap-style:
307 CapNotLast thin The results are device dependent, but
309 the desired effect is that nothing is
310 drawn.
311 CapButt thin The results are device dependent, but
312 the desired effect is that a single
313 pixel is drawn.
314 CapRound thin The results are the same as for Cap‐
315 Butt/thin.
316 CapProjecting thin The results are the same as for Cap‐
317 Butt/thin.
318 CapButt wide Nothing is drawn.
319 CapRound wide The closed path is a circle, centered at
320 the endpoint, and with the diameter
321 equal to the line-width.
322 CapProjecting wide The closed path is a square, aligned
323 with the coordinate axes, centered at
324 the endpoint, and with the sides equal
325 to the line-width.
326 For a line with coincident endpoints (x1=x2, y1=y2), when the join-
328 style is applied at one or both endpoints, the effect is as if the line
329 was removed from the overall path. However, if the total path consists
330 of or is reduced to a single point joined with itself, the effect is
331 the same as when the cap-style is applied at both endpoints.
332 The tile/stipple represents an infinite two-dimensional plane, with the
334 tile/stipple replicated in all dimensions. When that plane is superim‐
335 posed on the drawable for use in a graphics operation, the upper-left
336 corner of some instance of the tile/stipple is at the coordinates
337 within the drawable specified by the tile/stipple origin. The
338 tile/stipple and clip origins are interpreted relative to the origin of
339 whatever destination drawable is specified in a graphics request. The
340 tile pixmap must have the same root and depth as the GC, or a BadMatch
341 error results. The stipple pixmap must have depth one and must have
342 the same root as the GC, or a BadMatch error results. For stipple
343 operations where the fill-style is FillStippled but not FillOpaqueStip‐
344 pled, the stipple pattern is tiled in a single plane and acts as an
345 additional clip mask to be ANDed with the clip-mask. Although some
346 sizes may be faster to use than others, any size pixmap can be used for
347 tiling or stippling.
348 The fill-style defines the contents of the source for line, text, and
350 fill requests. For all text and fill requests (for example, XDrawText,
351 XDrawText16, XFillRectangle, XFillPolygon, and XFillArc); for line
352 requests with line-style LineSolid (for example, XDrawLine, XDrawSeg‐
353 ments, XDrawRectangle, XDrawArc); and for the even dashes for line
354 requests with line-style LineOnOffDash or LineDoubleDash, the following
355 apply:
356 FillSolid Foreground
358 FillTiled Tile
359 FillOpaqueStippled A tile with the same width and height as
360 stipple, but with background everywhere
361 stipple has a zero and with foreground
362 everywhere stipple has a one
363 FillStippled Foreground masked by stipple
364 When drawing lines with line-style LineDoubleDash, the odd dashes are
366 controlled by the fill-style in the following manner:
367 FillSolid Background
369 FillTiled Same as for even dashes
370 FillOpaqueStippled Same as for even dashes
371 FillStippled Background masked by stipple
372 Storing a pixmap in a GC might or might not result in a copy being
374 made. If the pixmap is later used as the destination for a graphics
375 request, the change might or might not be reflected in the GC. If the
376 pixmap is used simultaneously in a graphics request both as a destina‐
377 tion and as a tile or stipple, the results are undefined.
378 For optimum performance, you should draw as much as possible with the
380 same GC (without changing its components). The costs of changing GC
381 components relative to using different GCs depend on the display hard‐
382 ware and the server implementation. It is quite likely that some
383 amount of GC information will be cached in display hardware and that
384 such hardware can only cache a small number of GCs.
385 The dashes value is actually a simplified form of the more general pat‐
387 terns that can be set with XSetDashes. Specifying a value of N is
388 equivalent to specifying the two-element list [N, N] in XSetDashes.
389 The value must be nonzero, or a BadValue error results.
390 The clip-mask restricts writes to the destination drawable. If the
392 clip-mask is set to a pixmap, it must have depth one and have the same
393 root as the GC, or a BadMatch error results. If clip-mask is set to
394 None, the pixels are always drawn regardless of the clip origin. The
395 clip-mask also can be set by calling the XSetClipRectangles or XSetRe‐
396 gion functions. Only pixels where the clip-mask has a bit set to 1 are
397 drawn. Pixels are not drawn outside the area covered by the clip-mask
398 or where the clip-mask has a bit set to 0. The clip-mask affects all
399 graphics requests. The clip-mask does not clip sources. The clip-mask
400 origin is interpreted relative to the origin of whatever destination
401 drawable is specified in a graphics request.
402 You can set the subwindow-mode to ClipByChildren or IncludeInferiors.
404 For ClipByChildren, both source and destination windows are addition‐
405 ally clipped by all viewable InputOutput children. For IncludeInferi‐
406 ors, neither source nor destination window is clipped by inferiors.
407 This will result in including subwindow contents in the source and
408 drawing through subwindow boundaries of the destination. The use of
409 IncludeInferiors on a window of one depth with mapped inferiors of dif‐
410 fering depth is not illegal, but the semantics are undefined by the
411 core protocol.
412 The fill-rule defines what pixels are inside (drawn) for paths given in
414 XFillPolygon requests and can be set to EvenOddRule or WindingRule.
415 For EvenOddRule, a point is inside if an infinite ray with the point as
416 origin crosses the path an odd number of times. For WindingRule, a
417 point is inside if an infinite ray with the point as origin crosses an
418 unequal number of clockwise and counterclockwise directed path seg‐
419 ments. A clockwise directed path segment is one that crosses the ray
420 from left to right as observed from the point. A counterclockwise seg‐
421 ment is one that crosses the ray from right to left as observed from
422 the point. The case where a directed line segment is coincident with
423 the ray is uninteresting because you can simply choose a different ray
424 that is not coincident with a segment.
425 For both EvenOddRule and WindingRule, a point is infinitely small, and
427 the path is an infinitely thin line. A pixel is inside if the center
428 point of the pixel is inside and the center point is not on the bound‐
429 ary. If the center point is on the boundary, the pixel is inside if
430 and only if the polygon interior is immediately to its right (x
431 increasing direction). Pixels with centers on a horizontal edge are a
432 special case and are inside if and only if the polygon interior is
433 immediately below (y increasing direction).
434 The arc-mode controls filling in the XFillArcs function and can be set
436 to ArcPieSlice or ArcChord. For ArcPieSlice, the arcs are pie-slice
437 filled. For ArcChord, the arcs are chord filled.
438 The graphics-exposure flag controls GraphicsExpose event generation for
440 XCopyArea and XCopyPlane requests (and any similar requests defined by
441 extensions).
442
444 BadAlloc The server failed to allocate the requested resource or
445 server memory.
446 BadDrawable
448 A value for a Drawable argument does not name a defined Win‐
449 dow or Pixmap.
450 BadFont A value for a Font or GContext argument does not name a
452 defined Font.
453 BadGC A value for a GContext argument does not name a defined GCon‐
455 text.
456 BadMatch An InputOnly window is used as a Drawable.
458 BadMatch Some argument or pair of arguments has the correct type and
460 range but fails to match in some other way required by the
461 request.
462 BadPixmap A value for a Pixmap argument does not name a defined Pixmap.
464 BadValue Some numeric value falls outside the range of values accepted
466 by the request. Unless a specific range is specified for an
467 argument, the full range defined by the argument's type is
468 accepted. Any argument defined as a set of alternatives can
469 generate this error.
470
472 AllPlanes(3X11), XCopyArea(3X11), XCreateRegion(3X11), XDrawArc(3X11),
473 XDrawLine(3X11), XDrawRectangle(3X11), XDrawText(3X11), XFillRectan‐
474 gle(3X11), XQueryBestSize(3X11), XSetArcMode(3X11), XSetClipOri‐
475 gin(3X11), XSetFillStyle(3X11), XSetFont(3X11), XSetLineAt‐
476 tributes(3X11), XSetState(3X11), XSetTile(3X11)
477 Xlib - C Language X Interface
478 ()