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XCreateGC(3X11)          XLIB FUNCTIONS           XCreateGC(3X11)



NAME
     XCreateGC, XCopyGC, XChangeGC, XGetGCValues, XFreeGC, XGCon-
     textFromGC, XGCValues - create or free graphics contexts and
     graphics context structure

SYNTAX
     GC XCreateGC(display, d, valuemask, values)
           Display *display;
           Drawable d;
           unsigned long valuemask;
           XGCValues *values;

     XCopyGC(display, src, valuemask, dest)
           Display *display;
           GC src, dest;
           unsigned long valuemask;

     XChangeGC(display, gc, valuemask, values)
           Display *display;
           GC gc;
           unsigned long valuemask;
           XGCValues *values;

     Status XGetGCValues(display, gc, valuemask, values_return)
           Display *display;
           GC gc;
           unsigned long valuemask;
           XGCValues *values_return;

     XFreeGC(display, gc)
           Display *display;
           GC gc;

     GContext XGContextFromGC(gc)
           GC gc;

ARGUMENTS
     d         Specifies the drawable.

     dest      Specifies the destination GC.

     display   Specifies the connection to the X server.

     gc        Specifies the GC.

     src       Specifies the components of the source GC.

     valuemask Specifies which components in the GC are to be
               set, copied, changed, or returned . This argument
               is the bitwise inclusive OR of zero or more of the
               valid GC component mask bits.




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XCreateGC(3X11)          XLIB FUNCTIONS           XCreateGC(3X11)



     values    Specifies any values as specified by the
               valuemask.

     values_return
               Returns the GC values in the specified XGCValues
               structure.

DESCRIPTION
     The XCreateGC function creates a graphics context and
     returns a GC.  The GC can be used with any destination draw-
     able having the same root and depth as the specified draw-
     able.  Use with other drawables results in a BadMatch error.

     XCreateGC can generate BadAlloc, BadDrawable, BadFont, Bad-
     Match, BadPixmap, and BadValue errors.

     The XCopyGC function copies the specified components from
     the source GC to the destination GC.  The source and desti-
     nation GCs must have the same root and depth, or a BadMatch
     error results.  The valuemask specifies which component to
     copy, as for XCreateGC.

     XCopyGC can generate BadAlloc, BadGC, and BadMatch errors.

     The XChangeGC function changes the components specified by
     valuemask for the specified GC.  The values argument con-
     tains the values to be set.  The values and restrictions are
     the same as for XCreateGC.  Changing the clip-mask overrides
     any previous XSetClipRectangles request on the context.
     Changing the dash-offset or dash-list overrides any previous
     XSetDashes request on the context.  The order in which com-
     ponents are verified and altered is server dependent.  If an
     error is generated, a subset of the components may have been
     altered.

     XChangeGC can generate BadAlloc, BadFont, BadGC, BadMatch,
     BadPixmap, and BadValue errors.

     The XGetGCValues function returns the components specified
     by valuemask for the specified GC.  If the valuemask con-
     tains a valid set of GC mask bits (GCFunction, GCPlaneMask,
     GCForeground, GCBackground, GCLineWidth, GCLineStyle,
     GCCapStyle, GCJoinStyle, GCFillStyle, GCFillRule, GCTile,
     GCStipple, GCTileStipXOrigin, GCTileStipYOrigin, GCFont,
     GCSubwindowMode, GCGraphicsExposures, GCClipXOrigin, GCCLi-
     pYOrigin, GCDashOffset, or GCArcMode) and no error occurs,
     XGetGCValues sets the requested components in values_return
     and returns a nonzero status.  Otherwise, it returns a zero
     status.  Note that the clip-mask and dash-list (represented
     by the GCClipMask and GCDashList bits, respectively, in the
     valuemask) cannot be requested.  Also note that an invalid
     resource ID (with one or more of the three most significant



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XCreateGC(3X11)          XLIB FUNCTIONS           XCreateGC(3X11)



     bits set to 1) will be returned for GCFont, GCTile, and
     GCStipple if the component has never been explicitly set by
     the client.

     The XFreeGC function destroys the specified GC as well as
     all the associated storage.

     XFreeGC can generate a BadGC error.

STRUCTURES
     The XGCValues structure contains:

     /* GC attribute value mask bits */
     #define   GCFunction                  (1L<<0)
     #define   GCPlaneMask                 (1L<<1)
     #define   GCForeground                (1L<<2)
     #define   GCBackground                (1L<<3)
     #define   GCLineWidth                 (1L<<4)
     #define   GCLineStyle                 (1L<<5)
     #define   GCCapStyle                  (1L<<6)
     #define   GCJoinStyle                 (1L<<7)
     #define   GCFillStyle                 (1L<<8)
     #define   GCFillRule                  (1L<<9)
     #define   GCTile                      (1L<<10)
     #define   GCStipple                   (1L<<11)
     #define   GCTileStipXOrigin           (1L<<12)
     #define   GCTileStipYOrigin           (1L<<13)
     #define   GCFont                      (1L<<14)
     #define   GCSubwindowMode             (1L<<15)
     #define   GCGraphicsExposures         (1L<<16)
     #define   GCClipXOrigin               (1L<<17)
     #define   GCClipYOrigin               (1L<<18)
     #define   GCClipMask                  (1L<<19)
     #define   GCDashOffset                (1L<<20)
     #define   GCDashList                  (1L<<21)
     #define   GCArcMode                   (1L<<22)
     /* Values */

     typedef struct {
          int function;            /* logical operation */
          unsigned long plane_mask;/* plane mask */
          unsigned long foreground;/* foreground pixel */
          unsigned long background;/* background pixel */
          int line_width;          /* line width (in pixels) */
          int line_style;          /* LineSolid, LineOnOffDash, LineDoubleDash */
          int cap_style;           /* CapNotLast, CapButt, CapRound, CapProjecting */
          int join_style;          /* JoinMiter, JoinRound, JoinBevel */
          int fill_style;          /* FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
          int fill_rule;           /* EvenOddRule, WindingRule */
          int arc_mode;            /* ArcChord, ArcPieSlice */
          Pixmap tile;             /* tile pixmap for tiling operations */
          Pixmap stipple;          /* stipple 1 plane pixmap for stippling */



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XCreateGC(3X11)          XLIB FUNCTIONS           XCreateGC(3X11)



          int ts_x_origin;         /* offset for tile or stipple operations */
          int ts_y_origin;
          Font font;               /* default text font for text operations */
          int subwindow_mode;      /* ClipByChildren, IncludeInferiors */
          Bool graphics_exposures; /* boolean, should exposures be generated */
          int clip_x_origin;       /* origin for clipping */
          int clip_y_origin;
          Pixmap clip_mask;        /* bitmap clipping; other calls for rects */
          int dash_offset;         /* patterned/dashed line information */
          char dashes;
     } XGCValues;

     The function attributes of a GC are used when you update a
     section of a drawable (the destination) with bits from some-
     where else (the source). The function in a GC defines how
     the new destination bits are to be computed from the source
     bits and the old destination bits.  GXcopy is typically the
     most useful because it will work on a color display, but
     special applications may use other functions, particularly
     in concert with particular planes of a color display.  The
     16 GC functions, defined in &lt;X11/X.h&gt;, are:
     ______________________________________________
     Function Name     Value   Operation
     ______________________________________________































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     GXclear            0x0    0
     GXand              0x1    src AND dst
     GXandReverse       0x2    src AND NOT dst
     GXcopy             0x3    src
     GXandInverted      0x4    (NOT src) AND dst
     GXnoop             0x5    dst
     GXxor              0x6    src XOR dst
     GXor               0x7    src OR dst
     GXnor              0x8    (NOT src) AND (NOT
                               dst)
     GXequiv            0x9    (NOT src) XOR dst
     GXinvert           0xa    NOT dst
     GXorReverse        0xb    src OR (NOT dst)
     GXcopyInverted     0xc    NOT src
     GXorInverted       0xd    (NOT src) OR dst
     GXnand             0xe    (NOT src) OR (NOT
                               dst)
     GXset              0xf    1
     ______________________________________________

     Many graphics operations depend on either pixel values or
     planes in a GC.  The planes attribute is of type long, and
     it specifies which planes of the destination are to be modi-
     fied, one bit per plane.  A monochrome display has only one
     plane and will be the least significant bit of the word.  As
     planes are added to the display hardware, they will occupy
     more significant bits in the plane mask.

     In graphics operations, given a source and destination
     pixel, the result is computed bitwise on corresponding bits
     of the pixels.  That is, a Boolean operation is performed in
     each bit plane. The plane_mask restricts the operation to a
     subset of planes.  A macro constant AllPlanes can be used to
     refer to all planes of the screen simultaneously.  The
     result is computed by the following:

     ((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))

     Range checking is not performed on the values for fore-
     ground, background, or plane_mask.  They are simply trun-
     cated to the appropriate number of bits.  The line-width is
     measured in pixels and either can be greater than or equal
     to one (wide line) or can be the special value zero (thin
     line).

     Wide lines are drawn centered on the path described by the
     graphics request.  Unless otherwise specified by the join-
     style or cap-style, the bounding box of a wide line with
     endpoints [x1, y1], [x2, y2] and width w is a rectangle with
     vertices at the following real coordinates:





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     [x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
     [x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]

     Here sn is the sine of the angle of the line, and cs is the
     cosine of the angle of the line.  A pixel is part of the
     line and so is drawn if the center of the pixel is fully
     inside the bounding box (which is viewed as having infin-
     itely thin edges).  If the center of the pixel is exactly on
     the bounding box, it is part of the line if and only if the
     interior is immediately to its right (x increasing direc-
     tion).  Pixels with centers on a horizontal edge are a spe-
     cial case and are part of the line if and only if the inte-
     rior or the boundary is immediately below (y increasing
     direction) and the interior or the boundary is immediately
     to the right (x increasing direction).

     Thin lines (zero line-width) are one-pixel-wide lines drawn
     using an unspecified, device-dependent algorithm.  There are
     only two constraints on this algorithm.

     1.   If a line is drawn unclipped from [x1,y1] to [x2,y2]
          and if another line is drawn unclipped from
          [x1+dx,y1+dy] to [x2+dx,y2+dy], a point [x,y] is
          touched by drawing the first line if and only if the
          point [x+dx,y+dy] is touched by drawing the second
          line.

     2.   The effective set of points comprising a line cannot be
          affected by clipping.  That is, a point is touched in a
          clipped line if and only if the point lies inside the
          clipping region and the point would be touched by the
          line when drawn unclipped.

     A wide line drawn from [x1,y1] to [x2,y2] always draws the
     same pixels as a wide line drawn from [x2,y2] to [x1,y1],
     not counting cap-style and join-style.  It is recommended
     that this property be true for thin lines, but this is not
     required.  A line-width of zero may differ from a line-width
     of one in which pixels are drawn.  This permits the use of
     many manufacturers' line drawing hardware, which may run
     many times faster than the more precisely specified wide
     lines.

     In general, drawing a thin line will be faster than drawing
     a wide line of width one.  However, because of their dif-
     ferent drawing algorithms, thin lines may not mix well
     aesthetically with wide lines.  If it is desirable to obtain
     precise and uniform results across all displays, a client
     should always use a line-width of one rather than a line-
     width of zero.





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     The line-style defines which sections of a line are drawn:
     LineSolid       The full path of the line is drawn.

     LineDoub-       The full path of the line is drawn, but the
     leDash          even dashes are filled differently from the
                     odd dashes (see fill-style) with CapButt
                     style used where even and odd dashes meet.
     LineOnOffDash   Only the even dashes are drawn, and cap-style
                     applies to all internal ends of the indivi-
                     dual dashes, except CapNotLast is treated as
                     CapButt.

     The cap-style defines how the endpoints of a path are drawn:
     CapNotLast      This is equivalent to CapButt except that for
                     a line-width of zero the final endpoint is
                     not drawn.

     CapButt         The line is square at the endpoint (perpen-
                     dicular to the slope of the line) with no
                     projection beyond.
     CapRound        The line has a circular arc with the diameter
                     equal to the line-width, centered on the end-
                     point.  (This is equivalent to CapButt for
                     line-width of zero).

     CapProjecting   The line is square at the end, but the path
                     continues beyond the endpoint for a distance
                     equal to half the line-width.  (This is
                     equivalent to CapButt for line-width of
                     zero).

     The join-style defines how corners are drawn for wide lines:
     JoinMiter       The outer edges of two lines extend to meet
                     at an angle.  However, if the angle is less
                     than 11 degrees, then a JoinBevel join-style
                     is used instead.
     JoinRound       The corner is a circular arc with the diame-
                     ter equal to the line-width, centered on the
                     joinpoint.

     JoinBevel       The corner has CapButt endpoint styles with
                     the triangular notch filled.

     For a line with coincident endpoints (x1=x2, y1=y2), when
     the cap-style is applied to both endpoints, the semantics
     depends on the line-width and the cap-style:
     CapNotLast      thin    The results are device dependent, but
                             the desired effect is that nothing is
                             drawn.






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     CapButt         thin    The results are device dependent, but
                             the desired effect is that a single
                             pixel is drawn.

     CapRound        thin    The results are the same as for
                             CapButt/thin.
     CapProjecting   thin    The results are the same as for
                             CapButt/thin.

     CapButt         wide    Nothing is drawn.
     CapRound        wide    The closed path is a circle, centered at
                             the endpoint, and with the diameter
                             equal to the line-width.

     CapProjecting   wide    The closed path is a square, aligned
                             with the coordinate axes, centered at
                             the endpoint, and with the sides equal
                             to the line-width.

     For a line with coincident endpoints (x1=x2, y1=y2), when
     the join-style is applied at one or both endpoints, the
     effect is as if the line was removed from the overall path.
     However, if the total path consists of or is reduced to a
     single point joined with itself, the effect is the same as
     when the cap-style is applied at both endpoints.

     The tile/stipple represents an infinite two-dimensional
     plane, with the tile/stipple replicated in all dimensions.
     When that plane is superimposed on the drawable for use in a
     graphics operation, the upper-left corner of some instance
     of the tile/stipple is at the coordinates within the draw-
     able specified by the tile/stipple origin.  The tile/stipple
     and clip origins are interpreted relative to the origin of
     whatever destination drawable is specified in a graphics
     request.  The tile pixmap must have the same root and depth
     as the GC, or a BadMatch error results.  The stipple pixmap
     must have depth one and must have the same root as the GC,
     or a BadMatch error results. For stipple operations where
     the fill-style is FillStippled but not FillOpaqueStippled,
     the stipple pattern is tiled in a single plane and acts as
     an additional clip mask to be ANDed with the clip-mask.
     Although some sizes may be faster to use than others, any
     size pixmap can be used for tiling or stippling.

     The fill-style defines the contents of the source for line,
     text, and fill requests. For all text and fill requests (for
     example, XDrawText, XDrawText16, XFillRectangle, XFillPo-
     lygon, and XFillArc); for line requests with line-style
     LineSolid (for example, XDrawLine, XDrawSegments, XDrawRec-
     tangle, XDrawArc); and for the even dashes for line requests
     with line-style LineOnOffDash or LineDoubleDash, the follow-
     ing apply:



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     FillSolid            Foreground

     FillTiled            Tile
     FillOpaqueStippled   A tile with the same width and height as
                          stipple, but with background everywhere
                          stipple has a zero and with foreground
                          everywhere stipple has a one

     FillStippled         Foreground masked by stipple

     When drawing lines with line-style LineDoubleDash, the odd
     dashes are controlled by the fill-style in the following
     manner:
     FillSolid            Background
     FillTiled            Same as for even dashes

     FillOpaqueStippled   Same as for even dashes
     FillStippled         Background masked by stipple

     Storing a pixmap in a GC might or might not result in a copy
     being made.  If the pixmap is later used as the destination
     for a graphics request, the change might or might not be
     reflected in the GC.  If the pixmap is used simultaneously
     in a graphics request both as a destination and as a tile or
     stipple, the results are undefined.

     For optimum performance, you should draw as much as possible
     with the same GC (without changing its components).  The
     costs of changing GC components relative to using different
     GCs depend on the display hardware and the server implemen-
     tation.  It is quite likely that some amount of GC informa-
     tion will be cached in display hardware and that such
     hardware can only cache a small number of GCs.

     The dashes value is actually a simplified form of the more
     general patterns that can be set with XSetDashes.  Specify-
     ing a value of N is equivalent to specifying the two-element
     list [N, N] in XSetDashes.  The value must be nonzero, or a
     BadValue error results.

     The clip-mask restricts writes to the destination drawable.
     If the clip-mask is set to a pixmap, it must have depth one
     and have the same root as the GC, or a BadMatch error
     results.  If clip-mask is set to None, the pixels are always
     drawn regardless of the clip origin.  The clip-mask also can
     be set by calling the XSetClipRectangles or XSetRegion func-
     tions.  Only pixels where the clip-mask has a bit set to 1
     are drawn. Pixels are not drawn outside the area covered by
     the clip-mask or where the clip-mask has a bit set to 0.
     The clip-mask affects all graphics requests.  The clip-mask
     does not clip sources.  The clip-mask origin is interpreted
     relative to the origin of whatever destination drawable is



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     specified in a graphics request.

     You can set the subwindow-mode to ClipByChildren or Inclu-
     deInferiors.  For ClipByChildren, both source and destina-
     tion windows are additionally clipped by all viewable Inpu-
     tOutput children. For IncludeInferiors, neither source nor
     destination window is clipped by inferiors. This will result
     in including subwindow contents in the source and drawing
     through subwindow boundaries of the destination.  The use of
     IncludeInferiors on a window of one depth with mapped infe-
     riors of differing depth is not illegal, but the semantics
     are undefined by the core protocol.

     The fill-rule defines what pixels are inside (drawn) for
     paths given in XFillPolygon requests and can be set to
     EvenOddRule or WindingRule.  For EvenOddRule, a point is
     inside if an infinite ray with the point as origin crosses
     the path an odd number of times. For WindingRule, a point is
     inside if an infinite ray with the point as origin crosses
     an unequal number of clockwise and counterclockwise directed
     path segments.  A clockwise directed path segment is one
     that crosses the ray from left to right as observed from the
     point.  A counterclockwise segment is one that crosses the
     ray from right to left as observed from the point.  The case
     where a directed line segment is coincident with the ray is
     uninteresting because you can simply choose a different ray
     that is not coincident with a segment.

     For both EvenOddRule and WindingRule, a point is infinitely
     small, and the path is an infinitely thin line. A pixel is
     inside if the center point of the pixel is inside and the
     center point is not on the boundary. If the center point is
     on the boundary, the pixel is inside if and only if the
     polygon interior is immediately to its right (x increasing
     direction). Pixels with centers on a horizontal edge are a
     special case and are inside if and only if the polygon inte-
     rior is immediately below (y increasing direction).

     The arc-mode controls filling in the XFillArcs function and
     can be set to ArcPieSlice or ArcChord.  For ArcPieSlice, the
     arcs are pie-slice filled.  For ArcChord, the arcs are chord
     filled.

     The graphics-exposure flag controls GraphicsExpose event
     generation for XCopyArea and XCopyPlane requests (and any
     similar requests defined by extensions).

DIAGNOSTICS
     BadAlloc  The server failed to allocate the requested
               resource or server memory.

     BadDrawable



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               A value for a Drawable argument does not name a
               defined Window or Pixmap.

     BadFont   A value for a Font or GContext argument does not
               name a defined Font.

     BadGC     A value for a GContext argument does not name a
               defined GContext.

     BadMatch  An InputOnly window is used as a Drawable.

     BadMatch  Some argument or pair of arguments has the correct
               type and range but fails to match in some other
               way required by the request.

     BadPixmap A value for a Pixmap argument does not name a
               defined Pixmap.

     BadValue  Some numeric value falls outside the range of
               values accepted by the request.  Unless a specific
               range is specified for an argument, the full range
               defined by the argument's type is accepted.  Any
               argument defined as a set of alternatives can gen-
               erate this error.

SEE ALSO
     AllPlanes(3X11), XCopyArea(3X11), XCreateRegion(3X11),
     XDrawArc(3X11), XDrawLine(3X11), XDrawRectangle(3X11),
     XDrawText(3X11), XFillRectangle(3X11), XQueryBestSize(3X11),
     XSetArcMode(3X11), XSetClipOrigin(3X11),
     XSetFillStyle(3X11), XSetFont(3X11),
     XSetLineAttributes(3X11), XSetState(3X11), XSetTile(3X11)
     Xlib - C Language X Interface






















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