~ubuntu-branches/ubuntu/vivid/inform/vivid

<TR><TD Valign="top"><A HREF="contents.html">Contents</A> <A HREF="section31.html">Back</A> <A HREF="section33.html">Forward</A><TD bgcolor="#F5DEB3"><BLOCKQUOTE><H3>32. Boxes, menus and drawings</H3></BLOCKQUOTE><TR><TD><TD>

Yes, all right, I won't do the menu... I don't think you realise

how long it takes to do the menu, but no, it doesn't matter, I'll

hang the picture now. If the menus are late for lunch it doesn't

matter, the guests can all come and look at the picture till they

are ready, right?

...John Cleese and Connie Booth, Fawlty Towers</BLOCKQUOTE>

One harmless effect, though not very special, is to ask the player

a yes/no question. To do this, print up the question and then

call the library routine <TT>YesOrNo</TT>, which returns true/false

accordingly.

The status line is perhaps the most distinctive feature of Infocom games in

play. This is the (usually highlighted) bar across the top of the screen.

Usually, the game automatically prints the current game location, and either

the time or the score and number of turns taken. It has the score/turns

format unless the directive

<PRE>

Statusline time;

</PRE>

has been written in the program, in which case the game's 24-hour clock is

displayed.

<TR><TD Valign="top"><IMG SRC="icons/dbend.gif" ALT="/\"><TD bgcolor="#EEEEEE"> If you want to change this, just <TT>Replace</TT> the parser's

private <TT>DrawStatusLine</TT> routine. This requires a little assembly

language: see the next section for numerous examples.

About character graphic drawings: on some machines, text will by default

be displayed in a proportional font (i.e., one in which the width of a letter

depends on what it is, so that for example an 'i' will be narrower than an

'm'). If you want to display a diagram made up of letters, such as a map,

the spacing may then be wrong. The statement <TT>font off</TT> ensures that any

fancy font is switched off and that a fixed-pitch one is being used: after

this, <TT>font on</TT> restores the usual state.

<TR><TD Valign="top"><IMG SRC="icons/warning.gif" ALT="!!"><TD>WARNING: Don't turn the <TT>font</TT> on and off in the middle of a line; this

doesn't look right on some machines.

<TR><TD Valign="top"><IMG SRC="icons/dbend.gif" ALT="/\"><TD bgcolor="#EEEEEE"> When trying to produce a character-graphics drawing, you sometimes

want to produce the <TT>\</TT> character, one of the four "escape characters''

which can't normally be included in text. A double <TT>@</TT> sign followed by

a number includes the character with that ASCII code; thus:

<TT>@@64</TT> produces the literal character <TT>@</TT>

<TT>@@92</TT> produces <TT>\</TT><SAMP> </SAMP> <TT>@@94</TT> produces <TT>^</TT>

<SAMP> </SAMP> <TT>@@126</TT> produces <TT>~</TT>

</BLOCKQUOTE>

<TR><TD Valign="top"><IMG SRC="icons/ddbend.gif" ALT="/\/\"><TD bgcolor="#EEEEEE"> Some interpreters are capable of much better character graphics

(those equipped to run the Infocom game 'Beyond Zork', for instance).

There is a way to find out if this feature is provided and to make

use of it: see the Z-Machine Standards Document.

<TR><TD Valign="top"><IMG SRC="icons/ddbend.gif" ALT="/\/\"><TD bgcolor="#EEEEEE"> A single <TT>@</TT> sign is also an escape character. It must be

followed by a 2-digit decimal number between 0 and 31 (for instance,

<TT>@05</TT>). What this prints is the n-th 'variable string'. This feature

is not as useful as it looks, since the only legal values for such

a variable string are strings declared in advance by a <TT>LowString</TT>

directive. The <TT>String</TT> statement then sets the n-th variable

string. For details and an example, see the answer to the east-west

reversal exercise in <A HREF="section10.html">Section 10</A>.

A distinctive feature of later Infocom games was their use of epigrams.

The assembly language required to produce this effect is easy but a

nuisance, so there is an Inform statement to do it, <TT>box</TT>. For example,

<PRE>

box "I might repeat to myself, slowly and soothingly,"

"a list of quotations beautiful from minds profound;"

"if I can remember any of the damn things."

"-- Dorothy Parker";

</PRE>

100

Note that a list of one or more lines is given (without intervening commas)

101

and that a blank line is given by a null string. Remember that the text

102

cannot be too wide or it will look awful on a small screen. Inform

103

will automatically insert the boxed text into the game transcript,

104

if one is being made.

105

The author takes the view that this device is amusing for irrelevant

106

quotations but irritating when it conveys vital information (such as

107

"Beware of the Dog"). Also, some people might be running

108

your game on a laptop with a vertically challenged screen, so it is

109

polite to provide a "quotes off'' verb.

110

111

112

A snag with printing boxes is that if you do it in the middle of a turn

113

then it will probably scroll half-off the screen by the time the game

114

finishes printing for the turn. The right time to do so is just after

115

the prompt (usually <TT>></TT>) is printed, when the screen will definitely

116

scroll no more. You could use the <TT>Prompt:</TT> slot in <TT>LibraryMessages</TT>

117

to achieve this, but a more convenient way is to put your box-printing

118

into the entry point <TT>AfterPrompt</TT> (called at this time each

119

turn).

120

121

122

<TR><TD Valign="top"><IMG SRC="icons/exercise.gif" ALT="??"><TD bgcolor="#FBB9AC"><A NAME="ex88">EXERCISE 88: (link to <A HREF="answers2/answer88.html">the answer</A>)<TR><TD><TD> Implement a routine <TT>Quote(n)</TT> which will arrange for the

123

n-th quotation (where

124

0 <= n <= 49

125

) to be displayed at the end

126

of this turn, provided it hasn't been quoted

127

before.

128

129

130

131

132

Sometimes one would like to provide a menu of text options (for instance,

133

when producing instructions which have several topics, or when giving

134

clues). This can be done with the <TT>DoMenu</TT> routine, which imitates

135

the traditional "Invisiclues'' style. By setting <TT>pretty_flag=0</TT> you

136

can make a simple text version instead; a good idea for machines

137

with very small screens.

138

Here is a typical call to <TT>DoMenu</TT>:

139

<PRE>

140

DoMenu("There is information provided on the following:^

141

^ Instructions for playing

142

^ The history of this game

143

^ Credits^",

144

HelpMenu, HelpInfo);

145

</PRE>

146

147

Note the layout, and especially the carriage returns. The second and

148

third arguments are themselves routines. (Actually the first argument

149

can also be a routine to print a string instead of the string itself,

150

which might be useful for adaptive hints.) The <TT>HelpMenu</TT> routine

151

is supposed to look at the variable <TT>menu_item</TT>. In the case when this

152

is zero, it should return the number of entries in the menu (3 in the

153

example). In any case it should set <TT>item_name</TT> to the title for the

154

page of information for that item; and <TT>item_width</TT> to half its length

155

in characters (this is used to centre titles on the screen).

156

In the case of item 0, the title should be that for the whole

157

menu.

158

159

160

The second routine, <TT>HelpInfo</TT> above, should simply look at <TT>menu_item</TT>

161

(1 to 3 above) and print the text for that selection. After this returns,

162

normally the game prints "Press [Space] to return to menu'' but if

163

the value 2 is returned it doesn't wait, and if the value 3 is returned

164

it automatically quits the menu as if Q had been pressed. This is useful

165

for juggling submenus about.

166

167

168

Menu items can safely launch whole new menus, and it is easy to make

169

a tree of these (which will be needed when it comes to providing hints

170

across any size of game).

171

172

173

<TR><TD Valign="top"><IMG SRC="icons/exercise.gif" ALT="??"><TD bgcolor="#FBB9AC"><A NAME="ex89">EXERCISE 89: (link to <A HREF="answers2/answer89.html">the answer</A>)<TR><TD><TD> Code an "Invisiclues''-style sequence of hints for a puzzle,

174

revealed one at a time, as a menu item.

175

176

177

178

Finally, you can change the text style. The statement for this is

179

<TT>style</TT> and its effects are loosely modelled on the VT100 (design of

180

terminal). The style can be <TT>style roman</TT>, <TT>style bold</TT>, <TT>style reverse</TT> or

181

<TT>style underline</TT>. Again, poor terminals may not be able to display these,

182

so you shouldn't hide crucial information in them.

183

184

185

<TR><TD Valign="top"><IMG SRC="icons/refs.gif" ALT="*"><TD bgcolor="#EEEEEE">REFERENCES: 'Advent' contains a menu much like that above.

186

187

The "Infoclues'' utility program translates UHS format hints

188

(a standard, easy to read and write layout) into an Inform file of calls to

189

<TT>DoMenu</TT> which can simply be included into a game; this saves a good deal of

190

trouble.

191

</TABLE>

192

<HR><A HREF="contents.html">Contents</A> / <A HREF="section31.html">Back</A> / <A HREF="section33.html">Forward</A>

193

<A HREF="chapter1.html">Chapter I</A> / <A HREF="chapter2.html">Chapter II</A> / <A HREF="chapter3.html">Chapter III</A> / <A HREF="chapter4.html">Chapter IV</A> / <A HREF="chapter5.html">Chapter V</A> / <A HREF="chapter6.html">Chapter VI</A> / <A HREF="chapterA.html">Appendix</A><HR>Mechanically translated to HTML from third edition as revised 16 May 1997. Copyright © Graham Nelson 1993, 1994, 1995, 1996, 1997: all rights reserved.</BODY></HTML>

Older »