@Section
   @Title { Textures }
   @Tag { textures }
@Begin
@PP
The @Code "@Texture" symbol works in the same kind of way as @Code "@Font"
texture.sym @Index { @Code "@Texture" symbol }
and @Code "@Colour" do.  It causes the object to its right to be printed
in a texture specified by the object to its
left:
@ID @Code "striped @Texture 50p @Font ABC"
produces
@FootNote {
If you can't see the result here, or if you can see it but without
texture, then the fault is probably in your PostScript viewer.
The PostScript viewer used by the author (a 1997 version of @I { gv })
shows a blank space here and throughout this section wherever a
texture is supposed to appear, but when printed on his printer
the textures appear correctly.
}
@CD striped @Texture 50p @Font ABC
The object to the right of @Code "@Texture" may be arbitrary as usual.
@PP
# Textures are harder to specify than colours, and only a few
# texture names are widely used.
Only a handful of textures
are offered by the @Code "@Texture" symbol; but, as some
compensation, there are options which allow any texture to
be scaled, printed at any angle,
texture.sym @RawIndex { @Code "@Texture" symbol }
texture.sym.scale @SubIndex { @Code "scale" option }
texture.sym.angle @SubIndex { @Code "angle" option }
texture.sym.hshift @SubIndex { @Code "hshift" option }
texture.sym.vshift @SubIndex { @Code "vshift" option }
and shifted:
@ID @OneRow @Code @Verbatim {
striped @Texture
    scale { 2 }
    angle { 45d }
    hshift { 1p }
    vshift { 3p }
50p @Font ABC
}
produces
@CD striped @Texture
    scale { 2 }
    angle { 45d }
    hshift { 1p }
    vshift { 3p }
50p @Font ABC
with the texture scaled by a factor of 2, printed at an angle of 45
degrees, and shifted one point horizontally and three points
vertically.  The @Code scale option causes equal scaling in the
horizontal and vertical directions; there is also {@Code hscale}
which scales horizontally only, and @Code vscale which scales
vertically only.  As you would expect, the default values of these
options are @Code 1 for the scaling options, {@Code 0d} for {@Code angle},
and {@Code 0p} for {@Code hshift} and {@Code vshift}.
# @PP
# Stripes would rarely need to be shifted in practice, but some of the other
# textures described below can benefit from shifting.
@PP
Here is the list of all textures offered by the @Code "@Texture"
symbol, with the options specific to each kind of texture, their
default values, and sample default output.  Remember, all textures
take the {@Code angle}, {@Code scale}, {@Code hscale}, {@Code vscale},
{@Code hshift}, and {@Code vshift} options as well.
@ID @OneRow @Tbl
    mv { 0.5v }
    aformat { @Cell ml { 0i } A | @Cell @Code B | @Cell mr { 0i } @I lines @Break C }
{

@Rowa
    ma { 0i }
    A { @TextureSample solid }
    B {
"solid @Texture"
solid."texture" @Index { @Code "solid" "texture" }
}

@Rowa
    A { @TextureSample striped }
    B {
"striped @Texture"
"    width { 1p }"
"    gap { 1p }"
}
    C { ""
The width of each stripe
The width of each gap between stripes
striped."texture" @Index { @Code "striped" "texture" }
}

@Rowa
    A { @TextureSample grid }
    B {
"grid @Texture"
"    width { 1p }"
"    gap { 1p }"
}
    C { ""
The width of each stripe
grid."texture" @Index { @Code "grid" "texture" }
The width of each gap between stripes
}

@Rowa
    A { @TextureSample dotted }
    B {
"dotted @Texture"
"    radius { 0.5p }"
"    gap { 2p }"
}
    C { ""
The radius of each dot (filled circle)
dotted."texture" @Index { @Code "dotted" "texture" }
The gap between the centres of adjacent dots
}

@Rowa
    A { @TextureSample chessboard }
    B {
"chessboard @Texture"
"    width { 2p }"
}
    C { ""
The width of each square
chessboard."texture" @Index { @Code "chessboard" "texture" }
}

@Rowa
    A { @TextureSample brickwork }
    B {
"brickwork @Texture"
"    width { 6p }"
"    height { 2p }"
"    linewidth { 0.5p }"
}
    C { ""
The width of each brick
The height of each brick
brickwork."texture" @Index { @Code "brickwork" "texture" }
The width of the brickwork lines
}

@Rowa
    A { @TextureSample honeycomb }
    B {
"honeycomb @Texture"
"    radius { 2p }"
"    linewidth { 0.5p }"
}
    C { ""
The radius of each hexagon
honeycomb."texture" @Index { @Code "honeycomb" "texture" }
The width of the lines
}

@Rowa
    A { @TextureSample triangular }
    B {
"triangular @Texture"
"    radius { 4p }"
"    linewidth { 0.5p }"
}
    C { ""
The side length of each triangle
triangular."texture" @Index { @Code "triangular" "texture" }
The width of the lines
}

@Rowa
    mb { 0i }
    A { @TextureSample string }
    B {
"string @Texture"
"    width { 12p }"
"    height { 12p }"
"    font { Times-Roman }"
"    size { 10p }"
"    value { \"*\" }"
}
    C { ""
The width at which the string repeats
The height at which the string repeats
The font used to display the string (see below)
The font size used to display the string
string."texture" @Index { @Code "string" "texture" }
The characters to be displayed
}

}
This last example seems like a good one for experimenting with
the {@Code hshift} and {@Code vshift} options, so here goes:
texture.sym.hshift @SubIndex { @Code "hshift" option }
texture.sym.vshift @SubIndex { @Code "vshift" option }
@ID @OneRow @Tbl
    mv { 0.5v }
    aformat { @Cell ml { 0i } A | @Cell @Code B | @Cell mr { 0i } @I lines @Break C }
{
@Rowa
    mb { 0i }
    A {
@Box margin { 0i }
string @Texture hshift { 4p } vshift { 4p }
@Box margin { 2.0f } paint { black } {}
}
    B {
"string @Texture"
"    hshift { 4p }"
"    vshift { 4p }"
}
}
You have to find the right amount of shift by experiment, especially
when combined with rotation and scaling.  We recommend sticking to the
{@Code p} (points), {@Code m} (ems), {@Code c} (centimetres), and
{@Code i} (inches) units of measurement when giving length options
to {@Code "@Texture"} symbols.
@PP
Care is needed when using the @Code font and @Code value options
of {@Code "string @Texture"}, since these options are passed straight
through to the PostScript output without checking.  The @Code "font"
option takes a PostScript name for a font, not a Lout name.  Typical
PostScript font names, virtually certain to work, are {@Code Times-Roman}
and {@Code Helvetica}.  Since Lout takes no special steps to make sure
that the font you ask for is available, you should restrict your font
choices to fonts known to be in use elsewhere on the same page, or
known to be always loaded in your viewing device.  The @Code "value"
option must be a sequence of characters from the nominated font.
Although the value does not have to be quoted as shown, we recommend
it as a reminder of how limited the choices are here.  Also, spaces in
your value will work better between quotes, and to make parentheses --
@Code "(" and @Code ")" -- come out correctly they must be enclosed in
quotes and preceded by a backslash character, which you get as usual by
writing @I two backslash characters.  For example, {@Code "\"\\\\(\""}
will produce one left parenthesis.
@PP
Notice that {@Code "solid @Texture"} produces solid colour,
or in other words no texture:
@ID @Code @Verbatim {
striped @Texture angle { 45d }
@Box linewidth { 2p } solid @Texture 50p @Font WARNING!
}
produces
@CD {
striped @Texture angle { 45d }
@Box linewidth { 2p } solid @Texture 50p @Font WARNING!
}
As shown, {@Code "solid @Texture"} is useful for switching back to
normal printing within a textured region.  In this example, without
it the letters would have been striped as well.
@PP
Expert users can also make the object to the left of @Code "@Texture"
be anything that is acceptable to the left of the expert's symbol
{@Code "@SetTexture"}, allowing people who want to do some serious
work in PostScript to get arbitrary textures.  Consult the Expert's
Guide for more about this.
@End @Section