ml
71 lines
1.9 KiB
Go
71 lines
1.9 KiB
Go
package compression
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import "math/bits"
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// TilePaletteKey marks use of colors of a 256 palette.
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type TilePaletteKey struct {
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usedColors [4]uint64
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size int
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}
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// TilePaletteKeyFrom returns a key for the given slice of colors.
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func TilePaletteKeyFrom(colors []byte) TilePaletteKey {
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var key TilePaletteKey
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for _, c := range colors {
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key.UseColor(c)
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}
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return key
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}
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// Buffer returns the color indices marked in use by this key.
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func (key *TilePaletteKey) Buffer() []byte {
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result := make([]byte, 0, key.size)
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for i := 0; i < 256; i++ {
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if key.HasColor(byte(i)) {
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result = append(result, byte(i))
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}
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}
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return result
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}
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// UseColor marks the given color index in use.
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func (key *TilePaletteKey) UseColor(index byte) {
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if !key.HasColor(index) {
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key.usedColors[index/64] |= 1 << uint(index%64)
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key.size++
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}
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}
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// HasColor returns true if the given color index is in use by this key.
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func (key *TilePaletteKey) HasColor(index byte) bool {
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return (key.usedColors[index/64] & (1 << uint(index%64))) != 0
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}
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// Contains returns true if this key is equal to, or a superset of, the given key.
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func (key *TilePaletteKey) Contains(other *TilePaletteKey) bool {
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return ((^key.usedColors[0] & other.usedColors[0]) == 0) &&
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((^key.usedColors[1] & other.usedColors[1]) == 0) &&
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((^key.usedColors[2] & other.usedColors[2]) == 0) &&
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((^key.usedColors[3] & other.usedColors[3]) == 0)
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}
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// Without returns a new key instance that has all remaining colors marked in use.
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func (key *TilePaletteKey) Without(other *TilePaletteKey) TilePaletteKey {
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var result TilePaletteKey
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for i := 0; i < 4; i++ {
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result.usedColors[i] = key.usedColors[i] & ^other.usedColors[i]
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result.size += bits.OnesCount64(result.usedColors[i])
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}
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return result
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}
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// LessThan is a sorting function to order keys.
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func (key *TilePaletteKey) LessThan(other *TilePaletteKey) bool {
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for i := 0; i < 4; i++ {
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if key.usedColors[i] < other.usedColors[i] {
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return true
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}
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}
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return false
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}
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