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Attempt an implementation of StretchedAudioSource.

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This commit is contained in:
Thomas Harte 2024-01-29 16:45:20 -05:00
parent 15b5a62e01
commit 17cad73177
1 changed files with 57 additions and 11 deletions
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68
Machines/Apple/AppleII/AppleII.cpp
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@ -58,19 +58,65 @@ constexpr int MockingboardSlot = 4; // Conventional Mockingboard slot.
// * ... and hence seven pixels per memory access window clock in high-res mode, 14 in double high-res, etc.
constexpr float master_clock = 14318180.0;
template <typename SourceT>
/// Provides an audio source with will hold an instance of @c SourceT for audio generation, repeating one of its output samples
/// after every @c PacketClocks of output.
template <typename SourceT, std::size_t PacketClocks = 456>
class StretchedAudioSource {
public:
template <typename... Args>
StretchedAudioSource(Args &&... args) : source_(std::forward<Args>(args)...) {}
void get_samples(std::size_t number_of_samples, int16_t *target) {
// Approach should look something like — assuming a fully digital source_:
// Possible: the sample to duplicate fell exactly at the end of the last batch.
if(!remaining_packet_) {
remaining_packet_ = PacketClocks;
if constexpr (source_.get_is_stero()) {
target[0] = carry[0];
target[1] = carry[1];
target += 2;
} else {
target[0] = carry[0];
++target;
}
--number_of_samples;
}
// Divide required input into groups of PacketClocks samples; get all of those
// from the underlying source and then duplicate the final one.
//
// (1) sample_offset_ is always kept in the range [0, 912);
// (2) break down sample generation into 912-cycle blocks, getting the underlying source to provide
// the first 910 samples in each, then duplicate the final two.
//
// (possibly subject to an appropriate divider, with 'by two' being the obvious potential choice)
(void)number_of_samples;
(void)target;
// Duplicating into the current output packet won't be possible if it happens
// to line up exactly with the end of the PacketClocks, in which case hold a copy
// of the last level output in `carry` until next time.
while(number_of_samples) {
const auto target_length = std::min(number_of_samples, remaining_packet_);
source_.get_samples(target_length, target);
target += target_length * (1 + source_.get_is_stero());
number_of_samples -= target_length;
remaining_packet_ -= target_length;
if(!remaining_packet_) {
if(number_of_samples) {
remaining_packet_ = PacketClocks;
if constexpr (source_.get_is_stero()) {
target[0] = target[-2];
target[1] = target[-1];
target += 2;
} else {
target[0] = target[-1];
++target;
}
} else {
if constexpr (source_.get_is_stero()) {
carry[0] = target[-2];
carry[1] = target[-1];
} else {
carry[0] = target[-1];
}
}
}
}
}
// Direct passthroughs.
@ -82,9 +128,9 @@ class StretchedAudioSource {
private:
SourceT source_;
std::size_t sample_offset_ = 0;
static constexpr std::size_t clock_length = 7;
std::size_t remaining_packet_ = PacketClocks;
std::array<uint16_t, 2> carry;
};
}