This document describes non-standard additions to the Official OpenTTD NewGRF Specifications which are present in this patchpack. +
This additions MAY also be present in other patchpacks. They MAY be removed or moved in future, if necessary.
+NewGRFs which use any of these features SHOULD use the feature testing mechanism described below to check whether individual added features are supported.
+ +See Action 14 Specification for background information.
+Each FTST chunk (type C) describes an individual feature test.
+ Sub-chunks with each FTST chunk may appear in any order, however each sub-chunk SHOULD only appear ONCE within an individual FTST chunk.
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 obserable result (in global variable 0x9D) is equivalent to the case where all feature tests have failed, indicating that the feature is not present.
+Within an FTST chunk, the NAME text (type T) field contains the name of the feature to test for. The value of the language ID byte is ignored.
+ If the named feature is not present, or if this field is omitted, the version is 0.
+ If the named feature is present, the version number will be at least 1.
The feature testing mechanism itself has the feature name: feature_test, this document describes version 1.
+Within an FTST chunk, the MINV binary (type B) field contains the minimum (inclusive) (≥) version to accept. This is a Word (2 bytes).
+ The default value is 1.
Within an FTST chunk, the MINV binary (type B) field contains the maximum (inclusive) (≤) version to accept. This is a Word (2 bytes).
+ The default value is 0xFFFF (no maximum).
Within an FTST chunk, the SETP binary (type B) field contains the bit number to set/clear in
+ global variable 0x9D (TTD Platform) to store the result of the test. This is 1 byte.
+ If the test is successful, the bit is set (to 1), otherwise the bit is cleared (to 0).
+ 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.
+ Global variable 0x9D can then be tested by using a standard Action 7 or 9, or a standard Variational Action 2.
+ If this field is omitted, no bit is set or cleared, and the test is not observable.
+
+// Set bit 4 of global variable 0x9D if sample_feature_1 is present with a version of at least 4 +// Set bit 5 of global variable 0x9D if sample_feature_2 is present with a version of at least 5 and at most 6 +-1 * -1 14 + "C" "FTST" + "T" "NAME" 00 "sample_feature_1" 00 + "B" "MINV" \w2 \w4 + "B" "SETP" \w1 04 + 00 + 00 + "C" "FTST" + "T" "NAME" 00 "sample_feature_2" 00 + "B" "MINV" \w2 \w5 + "B" "MAXV" \w2 \w6 + "B" "SETP" \w1 05 + 00 + 00 +.... +// 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 ++
This is indicated by the feature name: action0_station_prop1B, version 1
+This is indicated by the feature name: action0_bridge_prop14, version 1
+This is indicated by the feature name: more_bridge_types, version 1
+This is indicated by the feature name: varaction2_station_var42, version 1
+ +