mc/server/world/chunk/sub_chunk.go

package chunk

import "slices"

// SubChunk is a cube of blocks located in a chunk. It has a size of 16x16x16 blocks and forms part of a stack
// that forms a Chunk.
type SubChunk struct {
	air        uint32
	storages   []*PalettedStorage
	blockLight []uint8
	skyLight   []uint8
}

// Equals returns if the sub chunk passed is equal to the current one.
func (sub *SubChunk) Equals(s *SubChunk) bool {
	if s.air != sub.air || len(s.storages) != len(sub.storages) {
		return false
	}

	for i, st := range s.storages {
		if !st.Equal(sub.storages[i]) {
			return false
		}
	}

	return true
}

// NewSubChunk creates a new sub chunk. All sub chunks should be created through this function.
func NewSubChunk(air uint32) *SubChunk {
	return &SubChunk{air: air}
}

// Clone returns an independent copy of the SubChunk.
func (sub *SubChunk) Clone() *SubChunk {
	clone := &SubChunk{
		air:        sub.air,
		storages:   make([]*PalettedStorage, len(sub.storages)),
		blockLight: cloneLight(sub.blockLight),
		skyLight:   cloneLight(sub.skyLight),
	}
	for i, storage := range sub.storages {
		clone.storages[i] = storage.Clone()
	}
	return clone
}

func cloneLight(light []uint8) []uint8 {
	if len(light) == 0 {
		return slices.Clone(light)
	}
	switch &light[0] {
	case noLightPtr:
		return noLight
	case fullLightPtr:
		return fullLight
	default:
		return slices.Clone(light)
	}
}

// Empty checks if the SubChunk is considered empty. This is the case if the SubChunk has 0 block storages or if it has
// a single one that is completely filled with air.
func (sub *SubChunk) Empty() bool {
	return len(sub.storages) == 0 || (len(sub.storages) == 1 && len(sub.storages[0].palette.values) == 1 && sub.storages[0].palette.values[0] == sub.air)
}

// Layer returns a certain block storage/layer from a sub chunk. If no storage at the layer exists, the layer
// is created, as well as all layers between the current highest layer and the new highest layer.
func (sub *SubChunk) Layer(layer uint8) *PalettedStorage {
	for uint8(len(sub.storages)) <= layer {
		// Keep appending to storages until the requested layer is achieved. Makes working with new layers
		// much easier.
		sub.storages = append(sub.storages, emptyStorage(sub.air))
	}
	return sub.storages[layer]
}

// Layers returns all layers in the sub chunk. This method may also return an empty slice.
func (sub *SubChunk) Layers() []*PalettedStorage {
	return sub.storages
}

// Block returns the runtime ID of the block located at the given X, Y and Z. X, Y and Z must be in a
// range of 0-15.
func (sub *SubChunk) Block(x, y, z byte, layer uint8) uint32 {
	if uint8(len(sub.storages)) <= layer {
		return sub.air
	}
	return sub.storages[layer].At(x, y, z)
}

// SetBlock sets the given block runtime ID at the given X, Y and Z. X, Y and Z must be in a range of 0-15.
func (sub *SubChunk) SetBlock(x, y, z byte, layer uint8, block uint32) {
	sub.Layer(layer).Set(x, y, z, block)
}

// SetBlockLight sets the block light value at a specific position in the sub chunk.
func (sub *SubChunk) SetBlockLight(x, y, z byte, level uint8) {
	if ptr := &sub.blockLight[0]; ptr == noLightPtr {
		// Copy the block light as soon as it is changed to create a COW system.
		sub.blockLight = append([]byte(nil), sub.blockLight...)
	}
	index := (uint16(x) << 8) | (uint16(z) << 4) | uint16(y)

	i := index >> 1
	bit := (index & 1) << 2
	sub.blockLight[i] = (sub.blockLight[i] & (0xf0 >> bit)) | (level << bit)
}

// BlockLight returns the block light value at a specific value at a specific position in the sub chunk.
func (sub *SubChunk) BlockLight(x, y, z byte) uint8 {
	index := (uint16(x) << 8) | (uint16(z) << 4) | uint16(y)
	return (sub.blockLight[index>>1] >> ((index & 1) << 2)) & 0xf
}

// SetSkyLight sets the skylight value at a specific position in the sub chunk.
func (sub *SubChunk) SetSkyLight(x, y, z byte, level uint8) {
	if ptr := &sub.skyLight[0]; ptr == fullLightPtr || ptr == noLightPtr {
		// Copy the skylight as soon as it is changed to create a COW system.
		sub.skyLight = append([]byte(nil), sub.skyLight...)
	}
	index := (uint16(x) << 8) | (uint16(z) << 4) | uint16(y)

	i := index >> 1
	bit := (index & 1) << 2
	sub.skyLight[i] = (sub.skyLight[i] & (0xf0 >> bit)) | (level << bit)
}

// SkyLight returns the skylight value at a specific value at a specific position in the sub chunk.
func (sub *SubChunk) SkyLight(x, y, z byte) uint8 {
	index := (uint16(x) << 8) | (uint16(z) << 4) | uint16(y)
	return (sub.skyLight[index>>1] >> ((index & 1) << 2)) & 0xf
}

// Compact cleans the garbage from all block storages that sub chunk contains, so that they may be
// cleanly written to a database.
func (sub *SubChunk) compact() {
	newStorages := make([]*PalettedStorage, 0, len(sub.storages))
	for _, storage := range sub.storages {
		storage.compact()
		if len(storage.palette.values) == 1 && storage.palette.values[0] == sub.air {
			// If the palette has only air in it, it means the storage is empty, so we can ignore it.
			continue
		}
		newStorages = append(newStorages, storage)
	}
	sub.storages = newStorages
}