Multi-layer rendering support

src/main/kotlin/mods/betterfoliage/render/pipeline/Layers.kt

@@ -0,0 +1,42 @@
+package mods.betterfoliage.render.pipeline
+
+import mods.betterfoliage.model.SpecialRenderData
+import mods.octarinecore.RenderTypeLookup
+import net.minecraft.block.Block
+import net.minecraft.client.renderer.RenderType
+import java.util.function.Predicate
+
+object Layers {
+    val tufts = RenderType.cutout()
+    val connectedGrass = RenderType.solid()
+    val connectedDirt = RenderType.cutoutMipped()
+    val coral = RenderType.cutoutMipped()
+}
+
+val defaultLayerBehaviour = Predicate<RenderType> { layer -> layer == RenderType.solid() }
+
+class WrappedLayerPredicate(val original: Predicate<RenderType>, val func: (RenderType, Predicate<RenderType>) -> Boolean) : Predicate<RenderType> {
+    override fun test(layer: RenderType) = func(layer, original)
+}
+
+/**
+ * Extension method to access the canRenderInLayer() predicate in [RenderTypeLookup]
+ */
+var Block.layerPredicate : Predicate<RenderType>?
+    get() = RenderTypeLookup.blockRenderChecks.getStatic()[delegate]
+    set(value) {
+        RenderTypeLookup.blockRenderChecks.getStatic()[delegate] = value!!
+    }
+
+/**
+ * Add a wrapper to the block's canRenderInLayer() predicate to enable dynamic multi-layer rendering.
+ * If the render data for the block implements [SpecialRenderData], the layers it enables will be
+ * rendered _in addition to_ the block's normal layers.
+ */
+fun Block.extendLayers() {
+    val original = layerPredicate ?: defaultLayerBehaviour
+    if (original !is WrappedLayerPredicate) layerPredicate = WrappedLayerPredicate(original) { layer, original ->
+        original.test(layer) ||
+        (RenderCtxBase.specialRenderData.get() as? SpecialRenderData)?.canRenderInLayer(layer) ?: false
+    }
+}