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PaletteLookupGenerator.go
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/
PaletteLookupGenerator.go
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package compression
import (
"context"
"math/bits"
"sort"
)
type paletteLookupEntry struct {
start int
size int
}
// PaletteLookup is a dictionary of tile delta data, found in a palette buffer.
type PaletteLookup struct {
buffer []byte
entries map[tilePaletteKey]paletteLookupEntry
}
// Buffer returns the underlying slice.
func (lookup *PaletteLookup) Buffer() []byte {
return lookup.buffer
}
// Lookup finds the given tile again and returns the properties where and how to reproduce it.
func (lookup *PaletteLookup) Lookup(tile tileDelta) (index int, pal []byte, mask uint64) {
key := tilePaletteKeyFrom(tile[:])
entry, inLookup := lookup.entries[key]
if inLookup {
index = entry.start
pal = lookup.buffer[entry.start : entry.start+entry.size]
} else {
pal = key.buffer()
}
var mapped [256]byte
for mappedIndex := len(pal) - 1; mappedIndex >= 0; mappedIndex-- {
mapped[pal[mappedIndex]] = byte(mappedIndex)
}
bitSize := uint(bits.Len(uint(len(pal) - 1)))
for tileIndex := PixelPerTile - 1; tileIndex >= 0; tileIndex-- {
mask <<= bitSize
mask |= uint64(mapped[tile[tileIndex]])
}
return
}
// PaletteLookupGenerator creates palette lookups based on a set of registered tiles.
type PaletteLookupGenerator struct {
keyUses map[tilePaletteKey]int
}
// Generate creates a lookup based on all currently registered tile deltas.
func (gen *PaletteLookupGenerator) Generate(ctx context.Context) (PaletteLookup, error) {
var lookup PaletteLookup
lookup.entries = make(map[tilePaletteKey]paletteLookupEntry)
remainder := make(map[tilePaletteKey]struct{})
for key := range gen.keyUses {
remainder[key] = struct{}{}
}
type sizedEntry struct {
entries map[tilePaletteKey]paletteLookupEntry
lastOffset int
}
sizedEntries := make(map[int]*sizedEntry)
knownSizes := []int{4, 8, 16}
for _, size := range knownSizes {
sizedEntries[size] = &sizedEntry{
entries: make(map[tilePaletteKey]paletteLookupEntry),
}
}
toDeleteCache := make([]tilePaletteKey, 0, len(remainder))
addToBuffer := func(data []byte) {
lookup.buffer = append(lookup.buffer, data...)
newSize := len(lookup.buffer)
for _, fitSize := range knownSizes {
fitLimit := newSize - fitSize
entry := sizedEntries[fitSize]
// remove all entries beyond a certain limit. as these bytes don't change, retrying won't help.
toDelete := toDeleteCache[0:0]
limit := newSize - 16 - len(data)
for key, entry := range entry.entries {
if entry.start < limit {
toDelete = append(toDelete, key)
}
}
for _, key := range toDelete {
delete(entry.entries, key)
}
// find any new keys
for start := entry.lastOffset; start < fitLimit; start++ {
tempKey := tilePaletteKeyFrom(lookup.buffer[start : start+fitSize])
if _, existing := entry.entries[tempKey]; !existing {
entry.entries[tempKey] = paletteLookupEntry{
start: start,
size: fitSize,
}
}
}
if fitLimit > 0 {
entry.lastOffset = fitLimit
}
}
}
addEarlyEntry := func(key tilePaletteKey, limitSize int) bool {
for _, fitSize := range knownSizes {
if key.size <= fitSize && fitSize <= limitSize {
entry := sizedEntries[fitSize]
for tempKey, paletteEntry := range entry.entries {
if tempKey.contains(&key) && (!key.hasColor(0x00) || (lookup.buffer[paletteEntry.start] == 0x00)) {
lookup.entries[key] = paletteEntry
return true
}
}
}
}
return false
}
sizeLimitForSize := map[int]int{3: 4, 4: 8, 5: 8, 6: 8, 7: 8, 8: 8, 9: 16, 10: 16, 11: 16, 12: 16, 13: 16, 14: 16, 15: 16, 16: 16}
for size := PixelPerTile; (size > 2) && (ctx.Err() == nil); size-- {
keysInSize := make([]tilePaletteKey, 0, len(remainder))
for key := range remainder {
if key.size == size {
keysInSize = append(keysInSize, key)
}
}
sort.Slice(keysInSize, func(a, b int) bool { return keysInSize[a].lessThan(&keysInSize[b]) })
// fmt.Printf("Working on key size %v, have %v sized, %v total remaining\n", size, len(keysInSize), len(remainder))
for _, sizedKey := range keysInSize {
if ctx.Err() != nil {
return PaletteLookup{}, ctx.Err()
}
{
var earlyRemoved []tilePaletteKey
for key := range remainder {
if addEarlyEntry(key, sizeLimitForSize[size]) {
earlyRemoved = append(earlyRemoved, key)
}
}
for _, key := range earlyRemoved {
delete(remainder, key)
}
}
if _, stillRemaining := remainder[sizedKey]; stillRemaining {
bytes := sizedKey.buffer()
lookup.entries[sizedKey] = paletteLookupEntry{start: len(lookup.buffer), size: len(bytes)}
addToBuffer(bytes)
delete(remainder, sizedKey)
}
}
}
return lookup, ctx.Err()
}
// Add registers a further delta to the generator.
func (gen *PaletteLookupGenerator) Add(delta tileDelta) {
key := tilePaletteKeyFrom(delta[:])
if key.size > 2 {
if gen.keyUses == nil {
gen.keyUses = make(map[tilePaletteKey]int)
}
gen.keyUses[key]++
}
}