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Ore features

Ore features are used to generate ores in the world. They are configured using the ore or scattered_ore feature types (ore is recommended for most cases).

Configuration

The following options are available for ore configurations:

Option Type Description
targets A list of TargetBlockStates A list which determines what block to use for specific targets. Needs a target and a state option. See below for more details.
size An int. (Range limit in Json is \([0;64]\)) Determines the volume size of the ore.
discard_chance_on_air_exposure A float. (Range limit in Json is \([0;1]\)) Determines the chance that the ore will be discarded if it is exposed to air. 1 means that the ore will never be exposed to air.

In code, the OreConfiguration class is used to configure the feature.

Targets

As mentioned above, the targets option is a list of targets. The target option is a so calledRuleTest. A RuleTest is pretty much the same thing as Predicate<BlockState> in Java. The state option is a BlockStateProvider which determines what block to use for the specific target.
The following RuleTests are available:

Name Description Example
minecraft:always_true Matches every block 
AlwaysTrueTest.INSTANCE

"target": {
  "predicate_type": "minecraft:always_true"
}
minecraft:block_match Matches a specific block 
BlockMatchTest(Blocks.STONE)

"target": {
  "predicate_type": "minecraft:block_match",
  "block": "minecraft:stone"
}
minecraft:blockstate_match Matches a specific blockstate 
BlockStateMatchTest(
    Blocks.GLASS_PANE.defaultBlockState()
        .setValue(IronBarsBlock.EAST, true)
        .setValue(IronBarsBlock.WEST, true)
)

"target": {
  "predicate_type": "minecraft:blockstate_match",
  "block_state": {
    "Name": "minecraft:glass_pane",
    "Properties": {
      "east": "true",
      "north": "false",
      "south": "false",
      "waterlogged": "false",
      "west": "true"
    }
  }
}
minecraft:tag_match Matches a specific block tag 
TagMatchTest(BlockTags.STONE_ORE_REPLACEABLES)

"target": {
  "predicate_type": "minecraft:tag_match",
  "tag": "minecraft:stone_ore_replaceables"
}
minecraft:random_block_match Matches the given block with a probability. The probability should be a value between 0.0 and 1.0. 
RandomBlockMatchTest(Blocks.COBBLESTONE, 0.5f)

"target": {
  "predicate_type": "minecraft:random_block_match",
  "block": "minecraft:cobblestone",
  "probability": 0.5
}
minecraft:random_blockstate_match Matches the given blockstate with a probability. The probability should be a value between 0.0 and 1.0. 
RandomBlockStateMatchTest(
    Blocks.GLASS_PANE.defaultBlockState()
        .setValue(IronBarsBlock.EAST, true)
        .setValue(IronBarsBlock.WEST, true),
    0.5f
)

"target": {
  "predicate_type": "minecraft:random_blockstate_match",
  "block_state": {
    "Name": "minecraft:glass_pane",
    "Properties": {
      "east": "true",
      "north": "false",
      "south": "false",
      "waterlogged": "false",
      "west": "true"
    }
  }
  "probability": 0.5
}
nova:material_match Matches a specific nova material 
MaterialMatchTest(Blocks.STAR_SHARDS_ORE)

"target": {
  "predicate_type": "nova:material_match",
  "material": "machines:star_shards_ore"
}
Custom RuleTests

You can also implement your own custom RuleTests by implementing the Minecraft RuleTest interface or extending Nova's NovaRuleTest/NovaMaterialTest classes. Nova's classes provide a bit more parameters such as the Level and BlockPos (or even the NovaMaterial via NovaMaterialTest).
You will also need to provide a RuleTestType, which specifies how your RuleTest implementation is (de)serialized. This can either be done by implementing the RuleTestType interface or creating it inline by just registering the Codec in the FeatureRegistry. Check out the Codecs page for more information on Mojang's serialization system.
Here's the code for Nova's MaterialMatchTest implementation as an example:

RuleTests.kt
val MATERIAL_MATCH_TEST_TYPE = FeatureRegistry.registerRuleTestType(Machines, "material_match", MaterialMatchTest.CODEC)
MaterialMatchTest.kt
class MaterialMatchTest(val material: BlockNovaMaterial) : NovaMaterialTest() {

    override fun test(material: BlockNovaMaterial, level: Level, pos: BlockPos, state: BlockState, random: RandomSource): Boolean {
        return material == this.material
    }

    override fun getType(): RuleTestType<*> = RuleTests.MATERIAL_MATCH_TEST_TYPE

    companion object {

        @JvmField // (1)!
        val CODEC: Codec<MaterialMatchTest> =
            BlockNovaMaterial.CODEC
                .fieldOf("material")
                .xmap(::MaterialMatchTest, MaterialMatchTest::material)
                .codec()
                .stable()
    }

}
  1. This allows CODEC to be accessed as a field from Java code instead of having to call getCODEC()
MaterialMatchTest.kt
object MaterialMatchTestType : RuleTestType<MaterialMatchTest> {

    private val CODEC: Codec<MaterialMatchTest> =
        BlockNovaMaterial.CODEC
            .fieldOf("material")
            .xmap(::MaterialMatchTest, MaterialMatchTest::material)
            .codec()
            .stable()

    override fun codec() = CODEC

}
RuleTests.kt
val MATERIAL_MATCH_TEST_TYPE = FeatureRegistry.registerRuleTestType(Machines, "material_match", MaterialMatchTestType)
MaterialMatchTest.kt
class MaterialMatchTest(val material: BlockNovaMaterial) : NovaMaterialTest() {

    override fun test(material: BlockNovaMaterial, level: Level, pos: BlockPos, state: BlockState, random: RandomSource): Boolean {
        return material == this.material
    }

    override fun getType(): RuleTestType<*> = MaterialMatchTestType

}

Example

As an example, here's the configured- and placed feature of star shards ore from the machines addon.

ConfiguredFeatures.kt
val ORE_STAR_SHARDS = FeatureRegistry.registerConfiguredFeature(
    Machines,
    "ore_star_shards",
    Feature.ORE,
    OreConfiguration(
        listOf( // (1)!
            OreConfiguration.target(
                TagMatchTest(BlockTags.STONE_ORE_REPLACEABLES),
                WrapperBlockState(Blocks.STAR_SHARDS_ORE) // (2)!
            ),
            OreConfiguration.target(
                TagMatchTest(BlockTags.DEEPSLATE_ORE_REPLACEABLES),
                WrapperBlockState(Blocks.DEEPSLATE_STAR_SHARDS_ORE)
            )
        ),
        4, // (3)!
        0.0f // (4)!
    )
)
  1. Specify that star_shards_ore should be used to replace normal stone and deepslate_star_shards_ore should be used to replace deepslate.
  2. Since blocks registered via Nova aren't registered in the vanilla blocks registry and thus don't have a blockstate, we need to wrap an block material in a WrapperBlockState.
    These objects are later detected before the block is placed and are passed to Nova for correct placement.
  3. The size of the ore vein.
  4. The chance that the ore will be discarded if it's exposed to air.

For placements, it's pretty useful to define a few util functions to create the PlacementModifier list.

PlacedFeatures.kt
private fun orePlacement(firstModifier: PlacementModifier, lastModifier: PlacementModifier) =
    listOf(firstModifier, InSquarePlacement.spread(), lastModifier, BiomeFilter.biome())

/**
 * @param count The amount of ores per chunk
 */
private fun commonOrePlacement(count: Int, lastModifier: PlacementModifier) =
    orePlacement(CountPlacement.of(count), lastModifier)

/**
 * @param chance The chance of an ore to spawn per chunk. 7 = 1 in 7 chunks
 */
private fun rareOrePlacement(chance: Int, lastModifier: PlacementModifier) =
    orePlacement(RarityFilter.onAverageOnceEvery(chance), lastModifier)
Vanilla ore placement examples 
// ore_iron_upper
commonOrePlacement(90, HeightRangePlacement.triangle(VerticalAnchor.absolute(80), VerticalAnchor.absolute(384)))
// ore_iron_middle
commonOrePlacement(10, HeightRangePlacement.triangle(VerticalAnchor.absolute(-24), VerticalAnchor.absolute(56)))
// ore_iron_small
commonOrePlacement(10, HeightRangePlacement.uniform(VerticalAnchor.bottom(), VerticalAnchor.absolute(72)))

// ore_diamond
commonOrePlacement(7, HeightRangePlacement.triangle(VerticalAnchor.aboveBottom(-80), VerticalAnchor.aboveBottom(80)))
// ore_diamond_large
rareOrePlacement(9, HeightRangePlacement.triangle(VerticalAnchor.aboveBottom(-80), VerticalAnchor.aboveBottom(80)))
// ore_diamond_buried
commonOrePlacement(4, HeightRangePlacement.triangle(VerticalAnchor.aboveBottom(-80), VerticalAnchor.aboveBottom(80)))
PlacedFeatures.kt
val ORE_STAR_SHARDS = FeatureRegistry.registerPlacedFeature(
    Machines,
    "ore_star_shards",
    ConfiguredFeatures.ORE_STAR_SHARDS,
    commonOrePlacement(30, HeightRangePlacement.uniform(VerticalAnchor.absolute(120), VerticalAnchor.top())) // (1)!
)
  1. 30 tries per chunk and only place the ore at a high altitude (y>120).
configured_feature/ore_star_shards.json
{
  "type": "minecraft:ore",
  "config": {
    "discard_chance_on_air_exposure": 0.0,
    "size": 4,
    "targets": [ // (1)!
      {
        "state": {
          "Name": "machines:star_shards_ore"
        },
        "target": {
          "predicate_type": "minecraft:tag_match",
          "tag": "minecraft:stone_ore_replaceables"
        }
      },
      {
        "state": {
          "Name": "machines:deepslate_star_shards_ore"
        },
        "target": {
          "predicate_type": "minecraft:tag_match",
          "tag": "minecraft:deepslate_ore_replaceables"
        }
      }
    ]
  }
  1. Specify that star_shards_ore should be used to replace normal stone and deepslate_star_shards_ore should be used to replace deepslate.
placed_feature/ore_star_shards.json
{
  "feature": "machines:ore_star_shards",
  "placement": [
    {
      "type": "minecraft:count",
      "count": 30 // (1)!
    },
    {
      "type": "minecraft:in_square" // (2)!
    },
    {
      "type": "minecraft:height_range", // (3)!
      "height": {
        "type": "minecraft:uniform",
        "max_inclusive": {
          "below_top": 0
        },
        "min_inclusive": {
          "absolute": 120
        }
      }
    },
    {
      "type": "minecraft:biome" // (4)!
    }
  ]
}
  1. 30 tries per chunk.
  2. Spread the tries in a square.
  3. Place the ore above y-level 119.
  4. Discard the try if we moved into a biome that doesn't generate star shards.