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40 lines
2.2 KiB
Markdown
40 lines
2.2 KiB
Markdown
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# Struck part index
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[API index](../API.md)
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`BlockMultipart.hitPartIndex(MovingObjectPosition)` returns the index of the part a multipart ray trace struck, or
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`-1` if the hit carries no part index.
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```java
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int index = BlockMultipart.hitPartIndex(hit);
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List<TMultiPart> parts = tile.jPartList();
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TMultiPart struck = index >= 0 && index < parts.size() ? parts.get(index) : null;
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```
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See the [compiling example](../../src/test/java/codechicken/multipart/examples/HitPartExample.java).
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## Where the index comes from
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`TileMultipart.rayTraceAll` asks each part in `jPartList()` order for its own hit. It then wraps each hit's data as
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`(index, partData)`, so a part that misses still uses up its index. `collisionRayTrace` returns the nearest of those
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hits. A hit from `BlockMultipart.collisionRayTrace` or `RayTracer.retraceBlock` on a multipart block goes through the
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same path.
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The index refers to the tile's part list when the trace ran. Adding or removing parts afterwards makes it stale, so
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retrace rather than keeping a hit across ticks. The method reads only the hit. It does not check coordinates, look
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up a tile or bounds-check the index. Retrieve the tile at the hit's block yourself, as the example does.
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`-1` means the hit is null, a plain `MovingObjectPosition`, or an `ExtendedMOP` whose data is not FMP's index pair.
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For example, another mod's tile can produce an `ExtendedMOP` with its own data.
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## Legacy compatibility
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`BlockMultipart.reduceMOP(MovingObjectPosition)` and its companion entry remain unchanged and are not deprecated.
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They return a `scala.Tuple2` of the boxed `Integer` index and a copy of the hit rebased onto the part's own data.
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FMP's activation, click, harvest, hardness, hit-effect, pick-block and highlight dispatch uses the rebased hit; there is no Java replacement for it
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because no consumer needs one.
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GT5U `5.09.54.205` reads `(Integer) BlockMultipart.reduceMOP(hit)._1()` to recolor ProjectRed wires. That call
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can become `hitPartIndex(hit)` with the same value and no Scala types. Keep the existing `hit instanceof ExtendedMOP`
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and coordinate checks, which protect the tile lookup. The released GT5U jar keeps linking the `Tuple2` descriptor,
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which stays until a migrated release is in the target pack.
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