ebiten/audio/loop.go

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// Copyright 2017 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package audio
import (
"fmt"
"io"
)
// InfiniteLoop represents a looped stream which never ends.
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type InfiniteLoop struct {
src io.ReadSeeker
lstart int64
llength int64
pos int64
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}
// NewInfiniteLoop creates a new infinite loop stream with a source stream and length in bytes.
func NewInfiniteLoop(src io.ReadSeeker, length int64) *InfiniteLoop {
return NewInfiniteLoopWithIntro(src, 0, length)
}
// NewInfiniteLoopWithIntro creates a new infinite loop stream with an intro part.
// NewInfiniteLoopWithIntro accepts a source stream src, introLength in bytes and loopLength in bytes.
func NewInfiniteLoopWithIntro(src io.ReadSeeker, introLength int64, loopLength int64) *InfiniteLoop {
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return &InfiniteLoop{
src: src,
lstart: introLength / bytesPerSample * bytesPerSample,
llength: loopLength / bytesPerSample * bytesPerSample,
pos: -1,
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}
}
func (i *InfiniteLoop) length() int64 {
return i.lstart + i.llength
}
func (i *InfiniteLoop) ensurePos() error {
if i.pos >= 0 {
return nil
}
pos, err := i.src.Seek(0, io.SeekCurrent)
if err != nil {
return err
}
if pos >= i.length() {
return fmt.Errorf("audio: stream position must be less than the specified length")
}
i.pos = pos
return nil
}
// Read is implementation of ReadSeeker's Read.
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func (i *InfiniteLoop) Read(b []byte) (int, error) {
if err := i.ensurePos(); err != nil {
return 0, err
}
if i.pos+int64(len(b)) > i.length() {
b = b[:i.length()-i.pos]
}
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n, err := i.src.Read(b)
i.pos += int64(n)
if i.pos > i.length() {
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panic(fmt.Sprintf("audio: position must be <= length but not at (*InfiniteLoop).Read: pos: %d, length: %d", i.pos, i.length()))
}
if err != nil && err != io.EOF {
return 0, err
}
if err == io.EOF || i.pos == i.length() {
pos, err := i.Seek(i.lstart, io.SeekStart)
if err != nil {
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return 0, err
}
i.pos = pos
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}
return n, nil
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}
// Seek is implementation of ReadSeeker's Seek.
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func (i *InfiniteLoop) Seek(offset int64, whence int) (int64, error) {
if err := i.ensurePos(); err != nil {
return 0, err
}
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next := int64(0)
switch whence {
case io.SeekStart:
next = offset
case io.SeekCurrent:
next = i.pos + offset
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case io.SeekEnd:
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return 0, fmt.Errorf("audio: whence must be io.SeekStart or io.SeekCurrent for InfiniteLoop")
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}
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if next < 0 {
return 0, fmt.Errorf("audio: position must >= 0")
}
if next >= i.lstart {
next = ((next - i.lstart) % i.llength) + i.lstart
}
// Ignore the new position returned by Seek since the source position might not be match with the position
// managed by this.
if _, err := i.src.Seek(next, io.SeekStart); err != nil {
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return 0, err
}
i.pos = next
return i.pos, nil
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}