<p>See <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action14">Action 14 Specification</a> for background information.</p>
<h4>Feature Test: C "FTST"</h4>
<p>Each FTST chunk (type C) describes an individual feature test.<br/>
Sub-chunks with each FTST chunk may appear in any order, however each sub-chunk SHOULD only appear ONCE within an individual FTST chunk.</p>
Sub-chunks within each FTST chunk may appear in any order, however each sub-chunk SHOULD only appear ONCE within an individual FTST chunk.</p>
<p>Feature tests can be safely used on implementations which do not implement the described feature test mechanism because unknown Action 14 blocks are ignored,
and the observable result (in global variable 0x9D) is equivalent to the case where all feature tests have failed, indicating that the feature is not present.</p>
<h4>Feature Name: C "FTST" -> T "NAME"</h4>
@ -58,7 +58,6 @@
"B" "MINV" \w2 \w4
"B" "SETP" \w1 04
00
00
"C" "FTST"
"T" "NAME" 00 "sample_feature_2" 00
"B" "MINV" \w2 \w5
@ -70,6 +69,75 @@
// Skip 1 sprite if bit 4 of global variable 0x9D is not set (indicating that sample_feature_1 with a version of at least 4 is NOT present)
-1 * -1 07 9D 01 \70 04 01
</pre>
<br/>
<h3id="feature-test">Action 14 - Property Mapping for Action 0</h3>
<p>See <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action14">Action 14 Specification</a> and <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action0">Action 0 Specification</a> for background information.</p>
<p>The property mapping mechanism has the feature name: <fontface="monospace">property_mapping</font>, this document describes version 1.</p>
<p>Users of this mechanism SHOULD at minimum use test for the presence of the feature above or test variable 8D, below.</p>
<h4>Property Mapping: C "A0PM"</h4>
<p>Each A0PM chunk (type C) describes an individual property mapping.<br/>
Sub-chunks within each A0PM chunk may appear in any order, however except where otherwise noted each sub-chunk SHOULD only appear ONCE within an individual A0PM chunk.</p>
<p>Property mapping can be safely used on implementations which do not implement the property mapping mechanism if Action 0 sprites which use mapped property IDs are skipped if one or more of:
<ul>
<li>The global variable 0x8D is checked to determine whether the property mapping operation was successful.</li>
<li>The feature name <fontface="monospace">property_mapping</font> is checked for.</li>
</ul>
Unknown Action 14 blocks are ignored, and do not need to be skipped.</p>
<h4>Property Name: C "A0PM" -> T "NAME"</h4>
<p>Within an A0PM chunk, the NAME text (type T) field contains the name of the property to map. The value of the language ID byte is ignored.</p>
<h4>Action 0 Feature ID: C "A0PM" -> B "FEAT"</h4>
<p>Within an A0PM chunk, the FEAT binary (type B) field contains the <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action0#Feature">Action 0 feature ID</a>. This is 1 byte.</p>
<h4>Property ID: C "A0PM" -> B "PROP"</h4>
<p>Within an A0PM chunk, the PROP binary (type B) field contains the property ID to allocate to the named property, this value can used in Action 0 sprites. This is 1 byte.<br/>
It is possible to override existing properties, however this use is not recommended.</p>
<h4>Success Indicator Global Variable 0x8D Bit: C "A0PM" -> B "SETT"</h4>
<p>Within an A0PM chunk, the SETT binary (type B) field contains the bit number to set/clear in
<ahref="https://newgrf-specs.tt-wiki.net/wiki/GlobalVariables">global variable</a> 0x8D (TTD version) to store whether the mapping operation was successful. This is 1 byte.<br/>
If the operation is successful, the bit is set (to 1), otherwise the bit is cleared (to 0).<br/>
The bit number MUST be in the range: 4 ≤ bit number ≤ 31. These bits can be assumed to be 0 on implementations which do not support this property mapping mechanism.<br/>
Global variable 0x8D can then be tested by using a standard <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action7">Action 7 or 9</a>, or a standard <ahref="https://newgrf-specs.tt-wiki.net/wiki/VariationalAction2">Variational Action 2</a>.<br/>
If this field is omitted, no bit is set or cleared.
</p>
<h4>Fallback Mode: C "A0PM" -> B "FLBK"</h4>
<p>Within an A0PM chunk, the FLBK binary (type B) field contains the fallback mode. This is 1 byte.<br/>
The fallback mode may take the following values:
<table>
<tr><th>Value</th><th>Behaviour</th></tr>
<tr><td>0</td><td>Attempts to map an unknown property name are ignored. Use of the mapped property in an Action 0 is ignored. This is the default.</td></tr>
<tr><td>1</td><td>Attempts to map an unknown property name are ignored. Use of the mapped property in an Action 0 is an error.</td></tr>
<tr><td>2</td><td>Attempting to map an unknown property name is an error.</td></tr>
</table>
Attempts to set a fallback mode other than those listed above are silently ignored. More fallback modes MAY be added in future versions of this mechanism.<br/>
This chunk MAY be specified more than once, in which case the last specified valid value is used.<br/>
Note that even when using fallback mode 0, above, if the property mapping feature is not present, then use of the mapped property ID in an Action 0 is an error.
</p>
<h4>Format of remapped properties</h4>
All properties which are mapped by the mechanism have the format:
/** Callback function for 'FTST'->'SETP' to set the maximum version of the feature being tested. */
/** Callback function for 'FTST'->'SETP' to set the bit number of global variable 9D (platform version) to set/unset with the result of the feature test. */
/** Callback function for 'A0PM'->'SETT' to set the bit number of global variable 8D (TTD version) to set/unset with whether the remapping was successful. */
Jonathan G Rennison
6 years ago