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56 lines
1.5 KiB
Go
56 lines
1.5 KiB
Go
// Package bufferdiff bounds comparisons of small dynamic GPU writes.
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// A change in offset or length makes the next upload independent.
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package bufferdiff
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import "bytes"
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const maximum = 16 << 10
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type LastWrite struct {
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at int
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data []byte
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}
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// ReserveSmall reserves backing for a known small buffer without suppressing its first full write; larger, partially used buffers acquire bounded comparison storage from actual writes.
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func (w *LastWrite) ReserveSmall(size int) {
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const limit = 1024
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if size > 0 && size <= limit && cap(w.data) < size {
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w.data = make([]byte, 0, size)
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}
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}
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func (w *LastWrite) Reset() { w.data = w.data[:0] }
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func (w *LastWrite) Delta(at int, data []byte) (int, []byte) {
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if len(data) > maximum {
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w.Reset()
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return at, data
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}
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if len(w.data) != len(data) || w.at != at {
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w.at = at
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w.data = append(w.data[:0], data...)
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return at, data
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}
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if bytes.Equal(w.data, data) {
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return at, nil
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}
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// Keep one contiguous GL command. Comparing coarse blocks avoids running
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// a byte-wise WASM loop over a long unchanged sprite or vertex prefix.
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const block = 32
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start, end := 0, len(data)
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for end-start >= block && bytes.Equal(w.data[start:start+block], data[start:start+block]) {
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start += block
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}
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for end-start >= block && bytes.Equal(w.data[end-block:end], data[end-block:end]) {
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end -= block
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}
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for start < end && w.data[start] == data[start] {
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start++
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}
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for start < end && w.data[end-1] == data[end-1] {
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end--
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}
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copy(w.data[start:end], data[start:end])
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return at + start, data[start:end]
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}
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