manipulating.html

linux图形界面x liberary手册

<B>JoinBevel</B>
join-style is used instead.

<TR><TD><B>JoinRound</B>
<TD>The corner is a circular arc with the diameter equal to the line-width, 
centered on the joinpoint.

<TR><TD><B>JoinBevel</B>
<TD>The corner has
<B>CapButt</B>
endpoint styles with the triangular notch filled.
</TABLE>

<P>

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:

<TABLE>
<TR><TD><B>CapNotLast</B>
<TD>thin
<TD>The results are device-dependent, 
but the desired effect is that nothing is drawn.

<TR><TD><B>CapButt</B>
<TD>thin
<TD>The results are device-dependent, 
but the desired effect is that a single pixel is drawn.

<TR><TD><B>CapRound</B>
<TD>thin
<TD>The results are the same as for
<B>CapButt</B>/thin.

<TR><TD><B>CapProjecting</B>
<TD>thin
<TD>The results are the same as for
<B>CapButt</B>/thin.

<TR><TD><B>CapButt</B>
<TD>wide
<TD>Nothing is drawn.

<TR><TD><B>CapRound</B>
<TD>wide
<TD>The closed path is a circle, centered at the endpoint, and
with the diameter equal to the line-width.

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

</TABLE>

<P>

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.

<A NAME="tile"></A>
<A NAME="stipple"></A>
<A NAME="tile-stipple-x-origin"></A>
<A NAME="tile-stipple-y-origin"></A>
<P>

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
<B>BadMatch</B>
error results.
The stipple pixmap must have depth one and must have the same root as the
GC, or a 
<B>BadMatch</B>
error results.  
For stipple operations where the fill-style is
<B>FillStippled</B>
but not 
<B>FillOpaqueStippled</B>,
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.

<A NAME="fill-style"></A>
<P>

The fill-style defines the contents of the source for line, text, and
fill requests.  
For all text and fill requests (for example,
<B><A HREF="../graphics/drawing-text/XDrawText.html">XDrawText()</A></B>, 
<B><A HREF="../graphics/drawing-text/XDrawText16.html">XDrawText16()</A></B>,
<B><A HREF="../graphics/filling-areas/XFillRectangle.html">XFillRectangle()</A></B>, 
<B><A HREF="../graphics/filling-areas/XFillPolygon.html">XFillPolygon()</A></B>, 
and
<B><A HREF="../graphics/filling-areas/XFillArc.html">XFillArc()</A></B>);
for line requests 
with <A HREF="manipulating.html#line-style">line-style</A> 
<B>LineSolid</B>
(for example,
<B><A HREF="../graphics/drawing/XDrawLine.html">XDrawLine()</A></B>,
<B><A HREF="../graphics/drawing/XDrawSegments.html">XDrawSegments()</A></B>, 
<B><A HREF="../graphics/drawing/XDrawRectangle.html">XDrawRectangle()</A></B>,
<B><A HREF="../graphics/drawing/XDrawArc.html">XDrawArc()</A></B>);
and for the even dashes for line requests with line-style 
<B>LineOnOffDash</B>
or 
<B>LineDoubleDash</B>,
the following apply:

<TABLE>
<TR><TD><B>FillSolid</B>
<TD>Foreground

<TR><TD><B>FillTiled</B>
<TD>Tile

<TR><TD><B>FillOpaqueStippled</B>
<TD>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

<TR><TD><B>FillStippled</B>
<TD>Foreground masked by stipple
</TABLE>

<P>

When drawing lines with line-style
<B>LineDoubleDash</B>,
the odd dashes are controlled by the fill-style in the following manner:

<TABLE>
<TR><TD><B>FillSolid</B>
<TD>Background

<TR><TD><B>FillTiled</B>
<TD>Same as for even dashes

<TR><TD><B>FillOpaqueStippled</B>
<TD>Same as for even dashes

<TR><TD><B>FillStippled</B>
<TD>Background masked by stipple
</TABLE>

<P>

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.

<P>

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 upon the display hardware and the server implementation.
It is quite likely that some amount of GC information will be
cached in display hardware and that such hardware can only cache a small number
of GCs.

<A NAME="dashes"></A>
<P>

The dashes value is actually a simplified form of the
more general patterns that can be set with 
<B><A HREF="convenience-functions/XSetDashes.html">XSetDashes()</A></B>.  
Specifying a
value of N is equivalent to specifying the two-element list [N, N] in 
<B><A HREF="convenience-functions/XSetDashes.html">XSetDashes()</A></B>. 
The value must be nonzero,
or a
<B>BadValue</B>
error results.

<A NAME="clip-mask"></A>
<P>

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
<B>BadMatch</B>
error results.
If clip-mask is set to
<B>None</B>,
the pixels are always drawn regardless of the clip origin.
The clip-mask also can be set by calling the
<B><A HREF="convenience-functions/XSetClipRectangles.html">XSetClipRectangles()</A></B>
or
<B><A HREF="../utilities/regions/XSetRegion.html">XSetRegion()</A></B>
functions.
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 specified in a graphics request.

<A NAME="subwindow-mode"></A>
<P>

You can set the subwindow-mode to
<B>ClipByChildren</B>
or
<B>IncludeInferiors</B>.
For 
<B>ClipByChildren</B>, 
both source and destination windows are
additionally clipped by all viewable 
<B><A HREF="../window/create.html#InputClass">InputOutput</A></B>
children.  
For 
<B>IncludeInferiors</B>,
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 
<B>IncludeInferiors</B>
on a window of one depth with mapped
inferiors of differing depth is not illegal, but the semantics are
undefined by the core protocol.

<A NAME="fill-rule"></A>
<P>

The fill-rule defines what pixels are inside (drawn) for
paths given in 
<B><A HREF="../graphics/filling-areas/XFillPolygon.html">XFillPolygon()</A></B>
requests and can be set to 
<B>EvenOddRule</B>
or
<B>WindingRule</B>.
For
<B>EvenOddRule</B>,
a point is inside if
an infinite ray with the point as origin crosses the path an odd number
of times.  
For 
<B>WindingRule</B>, 
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.

<P>

For both 
<B>EvenOddRule</B>
and
<B>WindingRule</B>,
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 interior is immediately below 
(y increasing direction).

<A NAME="arc-mode"></A>
<P>

The arc-mode controls filling in the 
<B><A HREF="../graphics/filling-areas/XFillArcs.html">XFillArcs()</A></B>
function and can be set to
<B>ArcPieSlice</B>
or
<B>ArcChord</B>.
For
<B>ArcPieSlice</B>,
the arcs are pie-slice filled.
For
<B>ArcChord</B>,
the arcs are chord filled.

<A NAME="graphics-exposure"></A>
<P>

The graphics-exposure flag controls 
<B><A HREF="../events/exposure/graphics-expose-and-no-expose.html">GraphicsExpose</A></B>
event generation
for 
<B><A HREF="../graphics/XCopyArea.html">XCopyArea()</A></B>
and 
<B><A HREF="../graphics/XCopyPlane.html">XCopyPlane()</A></B>
requests (and any similar requests defined by extensions).

<P>

To create a new GC that is usable on a given screen with a 
depth of drawable, use
<B><A HREF="XCreateGC.html">XCreateGC()</A></B>.

<P>

To copy components from a source GC to a destination GC, use
<B><A HREF="XCopyGC.html">XCopyGC()</A></B>.

<P>

To change the components in a given GC, use
<B><A HREF="XChangeGC.html">XChangeGC()</A></B>.

<P>

To obtain components of a given GC, use
<B><A HREF="XGetGCValues.html">XGetGCValues()</A></B>.

<P>

To free a given GC, use
<B><A HREF="XFreeGC.html">XFreeGC()</A></B>.

<P>

To obtain the 
<B><A HREF="/toto/GContext.html">GContext</A></B>
resource ID for a given GC, use 
<B><A HREF="XGContextFromGC.html">XGContextFromGC()</A></B>

<P>

Xlib usually defers sending changes to the components of a GC to the server
until a graphics function is actually called with that GC.
This permits batching of component changes into a single server request.
In some circumstances, however, it may be necessary for the client
to explicitly force sending the changes to the server.
An example might be when a protocol extension uses the GC indirectly,
in such a way that the extension interface cannot know what GC will be used.
To force sending GC component changes, use
<B><A HREF="XFlushGC.html">XFlushGC()</A></B>.

<H5 ALIGN=right><I>Next: <A HREF="convenience-functions/">Using GC Convenience Routines</A></I></H5>

<HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:[e-mail]">[e-mail]</A></ADDRESS>
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