'\" t

.\" Copyright \(co 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1994, 1996 X Consortium

.\"

.\" Permission is hereby granted, free of charge, to any person obtaining

.\" a copy of this software and associated documentation files (the

.\" "Software"), to deal in the Software without restriction, including

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.\" distribute, sublicense, and/or sell copies of the Software, and to

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.\" The above copyright notice and this permission notice shall be included

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.\" OTHER DEALINGS IN THE SOFTWARE.

.\"

.\" Except as contained in this notice, the name of the X Consortium shall

.\" not be used in advertising or otherwise to promote the sale, use or

.\" other dealings in this Software without prior written authorization

.\" from the X Consortium.

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.\" Copyright \(co 1985, 1986, 1987, 1988, 1989, 1990, 1991 by

.\" Digital Equipment Corporation

.\"

.\" Portions Copyright \(co 1990, 1991 by

.\" Tektronix, Inc.

.\"

.\" Permission to use, copy, modify and distribute this documentation for

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.\" copyright notice appears in all copies and that both that copyright notice

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.\" to this documentation without specific, written prior permission.

.\" Digital and Tektronix makes no representations about the suitability

.\" of this documentation for any purpose.

.\" It is provided ``as is'' without express or implied warranty.

.\" 

.\"

.ds xT X Toolkit Intrinsics \- C Language Interface

.ds xW Athena X Widgets \- C Language X Toolkit Interface

.ds xL Xlib \- C Language X Interface

.ds xC Inter-Client Communication Conventions Manual

.na

.de Ds

.nf

.\\$1D \\$2 \\$1

.ft CW

.\".ps \\n(PS

.\".if \\n(VS>=40 .vs \\n(VSu

.\".if \\n(VS<=39 .vs \\n(VSp

..

.de De

.ce 0

.if \\n(BD .DF

.nr BD 0

.in \\n(OIu

.if \\n(TM .ls 2

.sp \\n(DDu

.fi

..

.de IN		\" send an index entry to the stderr

..

.de Pn

.ie t \\$1\fB\^\\$2\^\fR\\$3

.el \\$1\fI\^\\$2\^\fP\\$3

..

.de ZN

.ie t \fB\^\\$1\^\fR\\$2

.el \fI\^\\$1\^\fP\\$2

..

.de hN

.ie t <\fB\\$1\fR>\\$2

.el <\fI\\$1\fP>\\$2

..

.ny0

'\" t

.TH XCreateGC __libmansuffix__ __xorgversion__ "XLIB FUNCTIONS"

.SH NAME

XCreateGC, XCopyGC, XChangeGC, XGetGCValues, XFreeGC, XGContextFromGC, XGCValues \- create or free graphics contexts and graphics context structure

.SH SYNTAX

.HP

GC XCreateGC\^(\^Display *\fIdisplay\fP\^, Drawable \fId\fP\^, unsigned long

\fIvaluemask\fP\^, XGCValues *\^\fIvalues\fP\^); 

.HP

int XCopyGC\^(\^Display *\fIdisplay\fP\^, GC \fIsrc\fP\^,

unsigned long \fIvaluemask\fP\^, GC \fIdest\fP\^); 

.HP

int XChangeGC\^(\^Display *\fIdisplay\fP\^, GC \fIgc\fP\^, unsigned long

\fIvaluemask\fP\^, XGCValues *\^\fIvalues\fP\^); 

.HP

Status XGetGCValues\^(\^Display *\fIdisplay\fP\^, GC \fIgc\fP\^, unsigned long

\fIvaluemask\fP\^, XGCValues *\fIvalues_return\fP\^); 

.HP

int XFreeGC\^(\^Display *\fIdisplay\fP\^, GC \fIgc\fP\^); 

.HP

GContext XGContextFromGC\^(\^GC \fIgc\fP\^); 

.SH ARGUMENTS

.IP \fId\fP 1i

Specifies the drawable. 

.IP \fIdest\fP 1i

Specifies the destination GC.

.IP \fIdisplay\fP 1i

Specifies the connection to the X server.

.IP \fIgc\fP 1i

Specifies the GC.

.IP \fIsrc\fP 1i

Specifies the components of the source GC.

.ds Vm set, copied, changed, or returned 

.IP \fIvaluemask\fP 1i

Specifies which components in the GC are to be \*(Vm. 

This argument is the bitwise inclusive OR of zero or more of the valid

GC component mask bits.

.IP \fIvalues\fP 1i

Specifies any values as specified by the valuemask.

.IP \fIvalues_return\fP 1i

Returns the GC values in the specified

.ZN XGCValues 

structure.

.SH DESCRIPTION

The

.ZN XCreateGC

function creates a graphics context and returns a GC.

The GC can be used with any destination drawable having the same root

and depth as the specified drawable.

Use with other drawables results in a

.ZN BadMatch

error.

.LP

.ZN XCreateGC

can generate

.ZN BadAlloc ,

.ZN BadDrawable ,

.ZN BadFont ,

.ZN BadMatch ,

.ZN BadPixmap ,

and

.ZN BadValue 

errors.

.LP

The

.ZN XCopyGC

function copies the specified components from the source GC

to the destination GC.

The source and destination GCs must have the same root and depth,

or a

.ZN BadMatch

error results.

The valuemask specifies which component to copy, as for

.ZN XCreateGC .

.LP

.ZN XCopyGC

can generate

.ZN BadAlloc ,

.ZN BadGC ,

and

.ZN BadMatch

errors.

.LP

The

.ZN XChangeGC

function changes the components specified by valuemask for

the specified GC.

The values argument contains the values to be set.

The values and restrictions are the same as for 

.ZN XCreateGC .

Changing the clip-mask overrides any previous 

.ZN XSetClipRectangles

request on the context. 

Changing the dash-offset or dash-list

overrides any previous 

.ZN XSetDashes

request on the context.

The order in which components are verified and altered is server dependent.

If an error is generated, a subset of the components may have been altered.

.LP

.ZN XChangeGC

can generate

.ZN BadAlloc ,

.ZN BadFont ,

.ZN BadGC ,

.ZN BadMatch ,

.ZN BadPixmap ,

and

.ZN BadValue 

errors.

.LP

The

.ZN XGetGCValues

function returns the components specified by valuemask for the specified GC.

If the valuemask contains a valid set of GC mask bits

.Pn ( GCFunction ,

.ZN GCPlaneMask ,

.ZN GCForeground ,

.ZN GCBackground ,

.ZN GCLineWidth ,

.ZN GCLineStyle ,

.ZN GCCapStyle ,

.ZN GCJoinStyle ,

.ZN GCFillStyle ,

.ZN GCFillRule ,

.ZN GCTile ,

.ZN GCStipple ,

.ZN GCTileStipXOrigin ,

.ZN GCTileStipYOrigin ,

.ZN GCFont ,

.ZN GCSubwindowMode ,

.ZN GCGraphicsExposures ,

.ZN GCClipXOrigin ,

.ZN GCCLipYOrigin ,

.ZN GCDashOffset ,

or

.ZN GCArcMode )

and no error occurs,

.ZN 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

.ZN GCClipMask

and 

.ZN 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 bits set to 1) will be returned for

.ZN GCFont ,

.ZN GCTile ,

and

.ZN GCStipple

if the component has never been explicitly set by the client.

.LP

The

.ZN XFreeGC

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

.LP

.ZN XFreeGC

can generate a

.ZN BadGC 

error.

.SH STRUCTURES

The

.ZN XGCValues

structure contains:

.LP

/\&* GC attribute value mask bits */

.TS

lw(.5i) lw(2.5i) lw(.75i).

\&#define	T{

.ZN GCFunction

T}	T{

(1L<<0)

T}

\&#define	T{

.ZN GCPlaneMask

T}	T{

(1L<<1)

T}

\&#define	T{

.ZN GCForeground

T}	T{

(1L<<2)

T}

\&#define	T{

.ZN GCBackground

T}	T{

(1L<<3)

T}

\&#define	T{

.ZN GCLineWidth

T}	T{

(1L<<4)

T}

\&#define	T{

.ZN GCLineStyle

T}	T{

(1L<<5)

T}

\&#define	T{

.ZN GCCapStyle

T}	T{

(1L<<6)

T}

\&#define	T{

.ZN GCJoinStyle

T}	T{

(1L<<7)

T}

\&#define	T{

.ZN GCFillStyle

T}	T{

(1L<<8)

T}

\&#define	T{

.ZN GCFillRule

T}	T{

(1L<<9)

T}

\&#define	T{

.ZN GCTile

T}	T{

(1L<<10)

T}

\&#define	T{

.ZN GCStipple

T}	T{

(1L<<11)

T}

\&#define	T{

.ZN GCTileStipXOrigin

T}	T{

(1L<<12)

T}

\&#define	T{

.ZN GCTileStipYOrigin

T}	T{

(1L<<13)

T}

\&#define	T{

.ZN GCFont

T}	T{

(1L<<14)

T}

\&#define	T{

.ZN GCSubwindowMode

T}	T{

(1L<<15)

T}

\&#define	T{

.ZN GCGraphicsExposures

T}	T{

(1L<<16)

T}

\&#define	T{

.ZN GCClipXOrigin

T}	T{

(1L<<17)

T}

\&#define	T{

.ZN GCClipYOrigin

T}	T{

(1L<<18)

T}

\&#define	T{

.ZN GCClipMask

T}	T{

(1L<<19)

T}

\&#define	T{

.ZN GCDashOffset

T}	T{

(1L<<20)

T}

\&#define	T{

.ZN GCDashList

T}	T{

(1L<<21)

T}

\&#define	T{

.ZN GCArcMode

T}	T{

(1L<<22)

T}

.TE

.IN "XGCValues" "" "@DEF@"

.LP

.Ds 0

/\&* 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 */

        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;

.De

.LP

The function attributes of a GC are used when you update a section of

a drawable (the destination) with bits from somewhere 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.

.ZN 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 

.hN X11/X.h ,

are:

.\" are listed in Table 5-1 along with the 

.\"the associated hexadecimal code

.\" and operation.

.\".CP T 1

.\"Display Functions

.TS

lw(1.5i) cw(.5i) lw(2i).

_

.sp 6p

.B

Function Name	Value	Operation

.sp 6p

_

.sp 6p

T{

.ZN GXclear

T}	T{

0x0

T}	T{

0

T}

T{

.ZN GXand

T}	T{

0x1

T}	T{

src AND dst

T}

T{

.ZN GXandReverse

T}	T{

0x2

T}	T{

src AND NOT dst

T}

T{

.ZN GXcopy

T}	T{

0x3

T}	T{

src

T}

T{

.ZN GXandInverted

T}	T{

0x4

T}	T{

(NOT src) AND dst

T}

T{

.ZN GXnoop

T}	T{

0x5

T}	T{

dst

T}

T{

.ZN GXxor

T}	T{

0x6

T}	T{

src XOR dst

T}

T{

.ZN GXor

T}	T{

0x7

T}	T{

src OR dst

T}

T{

.ZN GXnor

T}	T{

0x8

T}	T{

(NOT src) AND (NOT dst)

T}

T{

.ZN GXequiv

T}	T{

0x9

T}	T{

(NOT src) XOR dst

T}

T{

.ZN GXinvert

T}	T{

0xa

T}	T{

NOT dst

T}

T{

.ZN GXorReverse

T}	T{

0xb

T}	T{

src OR (NOT dst)

T}

T{

.ZN GXcopyInverted

T}	T{

0xc

T}	T{

NOT src

T}

T{

.ZN GXorInverted

T}	T{

0xd

T}	T{

(NOT src) OR dst

T}

T{

.ZN GXnand

T}	T{

0xe

T}	T{

(NOT src) OR (NOT dst)

T}

T{

.ZN GXset

T}	T{

0xf

T}	T{

1

T}

.sp 6p

_

.TE

.LP

Many graphics operations depend on either pixel values or planes in a GC.

.IN "Pixel value"

The planes attribute is of type long, and it specifies which planes of the

destination are to be modified, one bit per plane.

.IN "Plane" "mask"

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.

.LP

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

.ZN AllPlanes

can be used to refer to all planes of the screen simultaneously.

The result is computed by the following:

.LP

.Ds 

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

.De

.LP

Range checking is not performed on the values for foreground,

background, or plane_mask.

They are simply truncated 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).

.LP

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:

.LP

.Ds

[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)]

.De

.LP

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 infinitely 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 direction).

Pixels with centers on a horizontal edge are a special case and are part of

the line if and only if the interior or the boundary is immediately below 

(y increasing direction) and the interior or the boundary is immediately

to the right (x increasing direction).

.LP

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. 

.IP 1. 5

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.

.IP 2. 5

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.

.LP

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.

.LP

In general, 

drawing a thin line will be faster than drawing a wide line of width one.

However, because of their different 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.

.LP

The line-style defines which sections of a line are drawn:

.TS

lw(1.3i) lw(4.5i).

T{

.ZN LineSolid

T}	T{

The full path of the line is drawn.

T}

.sp 6p

T{

.ZN LineDoubleDash

T}	T{

The full path of the line is drawn, 

but the even dashes are filled differently 

from the odd dashes (see fill-style) with

.ZN CapButt 

style used where even and odd dashes meet.

T}

.sp 6p

T{

.ZN LineOnOffDash

T}	T{

Only the even dashes are drawn,

and cap-style applies to 

all internal ends of the individual dashes,

except 

.ZN CapNotLast

is treated as 

.ZN CapButt . 

T}

.TE

.LP

The cap-style defines how the endpoints of a path are drawn:

.IN "Graphics context" "path"

.TS

lw(1.3i) lw(4.5i).

T{

.ZN CapNotLast

T}	T{

This is equivalent to 

.ZN CapButt  

except that for a line-width of zero the final endpoint is not drawn.

T}

.sp 6p

T{

.ZN CapButt

T}	T{

The line is square at the endpoint (perpendicular to the slope of the line)

with no projection beyond.

T}

.sp 6p

T{

.ZN CapRound

T}	T{

The line has a circular arc with the diameter equal to the line-width,

centered on the endpoint.

(This is equivalent to 

.ZN CapButt 

for line-width of zero).

T}

.sp 6p

T{

.ZN CapProjecting

T}	T{

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 

.ZN CapButt 

for line-width of zero).

T}

.TE

.LP

The join-style defines how corners are drawn for wide lines:

.TS

lw(1.3i) lw(4.5i).

T{

.ZN JoinMiter

T}	T{

The outer edges of two lines extend to meet at an angle.

However, if the angle is less than 11 degrees,

then a

.ZN JoinBevel

join-style is used instead.

T}

.sp 6p

T{

.ZN JoinRound

T}	T{

The corner is a circular arc with the diameter equal to the line-width, 

centered on the joinpoint.

T}

.sp 6p

T{

.ZN JoinBevel

T}	T{

The corner has

.ZN CapButt 

endpoint styles with the triangular notch filled.

T}

.TE

.LP

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:

.TS

lw(1.3i) lw(.5i) lw(4i).

T{

.ZN CapNotLast

T}	T{

thin

T}	T{

The results are device dependent, 

but the desired effect is that nothing is drawn.

T}

.sp 6p

T{

.ZN CapButt

T}	T{

thin

T}	T{

The results are device dependent, 

but the desired effect is that a single pixel is drawn.

T}

.sp 6p

T{

.ZN CapRound

T}	T{

thin

T}	T{

The results are the same as for

.ZN CapButt /thin.

T}

.sp 6p

T{

.ZN CapProjecting

T}	T{

thin

T}	T{

The results are the same as for

.ZN CapButt /thin.

T}

.sp 6p

T{

.ZN CapButt

T}	T{

wide

T}	T{

Nothing is drawn.

T}

.sp 6p

T{

.ZN CapRound

T}	T{

wide

T}	T{

The closed path is a circle, centered at the endpoint, and

with the diameter equal to the line-width.

T}

.sp 6p

T{

.ZN CapProjecting

T}	T{

wide

T}	T{

The closed path is a square, aligned with the coordinate axes, centered at the

endpoint, and with the sides equal to the line-width.

T}

.TE

.LP

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.

.LP

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 drawable 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

.ZN BadMatch 

error results.

The stipple pixmap must have depth one and must have the same root as the

GC, or a 

.ZN BadMatch 

error results.  

For stipple operations where the fill-style is

.ZN FillStippled

but not 

.ZN 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.

.LP

The fill-style defines the contents of the source for line, text, and

fill requests.  

For all text and fill requests (for example,

.ZN XDrawText , 

.ZN XDrawText16 ,

.ZN XFillRectangle , 

.ZN XFillPolygon , 

and

.ZN XFillArc );

for line requests 

with line-style 

.ZN LineSolid 

(for example,

.ZN XDrawLine ,

.ZN XDrawSegments , 

.ZN XDrawRectangle ,

.ZN XDrawArc );

and for the even dashes for line requests with line-style 

.ZN LineOnOffDash 

or 

.ZN LineDoubleDash ,

the following apply:

.TS

lw(1.8i) lw(4i).

T{

.ZN FillSolid

T}	T{

Foreground

T}

.sp 6p

T{

.ZN FillTiled

T}	T{

Tile

T}

.sp 6p

T{

.ZN FillOpaqueStippled

T}	T{

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

T}

.sp 6p

T{

.ZN FillStippled

T}	T{

Foreground masked by stipple

T}

.TE

.LP

When drawing lines with line-style