<h2>Additions to NewGRF Specifications in JGR's Patchpack</h2>
<p>This document describes non-standard additions to the <ahref="https://newgrf-specs.tt-wiki.net/wiki/Main_Page">Official OpenTTD NewGRF Specifications</a> which are present in this patchpack.
<p>A subset of the features listed below are also supported in a fork of NML, see the associated <ahref="newgrf-additions-nml.html">NML document</a> for more details.</p>
<p>NewGRFs which use any of these features SHOULD use the <ahref="#feature-test">feature testing</a> mechanism described below to check whether individual added features are supported.</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>
<p>Within an FTST chunk, the SETP binary (type B) field contains the bit number to set/clear in
<ahref="https://newgrf-specs.tt-wiki.net/wiki/GlobalVariables">global variable</a> 0x9D (TTD Platform) to store the result of the test. This is 1 byte.<br/>
If the test 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 feature test mechanism.<br/>
Global variable 0x9D 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, and the test is not observable.
<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>
<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>
<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>
<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>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.
Note that each use of the mapped property ID is followed by Num-info iterations of the size and data pair above. See: <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action0">Action 0 Specification</a>.
<p>This property allows building bridges over stations.<br/>
The bridge height property defines minimum clearances required for a bridge for each of the 8 station layouts (or 0 to not allow any bridge). Values are given in height level units (1 level == 8px).<br/>
Each height value is 1 byte, the total property length is 8 bytes.
<h4id="railtype_enable_programmable_signals">Enable custom signal sprites for programmable pre-signals (mappable property: railtype_enable_programmable_signals)</h4>
<h4id="railtype_enable_restricted_signals">Enable restricted signal flag for custom signal sprites (mappable property: railtype_enable_restricted_signals)</h4>
<p>This applies to <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action3/Railtypes#Signal_sprites_.280B.29">Action 2/3 - Railtype custom signal sprites</a>.<br/>
When enabled, bit 24 of variable 18 (extra callback info) is set if the signal is restricted (has a routing restriction program attached).<br/>
<h4id="railtype_disable_realistic_braking">Disable use of realistic braking with this rail type (mappable property: railtype_disable_realistic_braking)</h4>
<p>This applies to <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action3/Railtypes#Signal_sprites_.280B.29">Action 2/3 - Railtype custom signal sprites</a>.<br/>
When this property is set realistic braking is disabled for trains of this railtype even when realistic braking is otherwise in effect.<br/>
The property length is 1 byte. 0 is realistic braking is not disabled for this railtype. 1 is disable realistic braking for this railtype.
</p>
<p>This is indicated by the feature name: <fontface="monospace">action0_railtype_disable_realistic_braking</font>, version 1</p>
<p>See <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action14">Action 14 Specification</a> and <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action5">Action 5 Specification</a> for background information.</p>
<p>The action 5 type ID mapping mechanism has the feature name: <fontface="monospace">action5_type_id_mapping</font>, this document describes version 1.</p>
<p>Users of this mechanism SHOULD at minimum test for the presence of the feature above or test variable 8D, below.</p>
<p>Each A5TM chunk (type C) describes an individual action 5 type ID mapping.<br/>
Sub-chunks within each A5TM chunk may appear in any order, however except where otherwise noted each sub-chunk SHOULD only appear ONCE within an individual A5TM chunk.</p>
<p>Action 5 type ID mapping can be safely used on implementations which do not implement the type ID mapping mechanism if Action 5 sprites which use mapped type IDs are skipped if one or more of:
<ul>
<li>The global variable 0x8D is checked to determine whether the type ID mapping operation was successful.</li>
<li>The feature name <fontface="monospace">action5_type_id_mapping</font> is checked for.</li>
</ul>
Unknown Action 14 blocks are ignored, and do not need to be skipped.</p>
<p>Within an A5TM chunk, the TYPE binary (type B) field contains the type ID to allocate to the named type, this value can used in Action 5 sprites. This is 1 byte. The value MUST be < 128 (i.e bit 7 must be clear).<br/>
It is possible to override existing type IDs, however this use is not recommended.</p>
<p>Signal graphics come in groups of 16. These groups contain sprites in the same order as sprites 1275-1290 in trg1[r].grf and <ahref="https://newgrf-specs.tt-wiki.net/wiki/Action5#04_Signal_graphics.">Action 5 type 4 (signals)</a>;
red, then green, for each of: SW-facing, NE-facing, NW-facing, SE-facing, E-facing, W-facing, S-facing, N-facing.
