looper/backends/playback/zsm/zsm_backend.cpp

#include "zsm_backend.hpp"
extern "C" {
#include "x16emu/audio.h"
#include "x16emu/vera_pcm.h"
#include "x16emu/vera_psg.h"
#include "x16emu/ymglue.h"
}
#include <exception>
#include <filesystem>
#include "file_backend.hpp"
#include <stddef.h>
#include <string.h>
#include <file_backend.hpp>
void ZsmBackend::load(const char *filename) {
    spec.format = AUDIO_S16SYS;
    spec.samples = SAMPLES_PER_BUFFER;
    spec.channels = 2;
    spec.size = spec.samples * SAMPLE_BYTES;
    file = open_file(filename);
    char magic[2];
    file->read(magic, 2, 1);
    if (magic[0] != 0x7a || magic[1] != 0x6d) {
        throw std::exception();
    }
    uint8_t version;
    file->read(&version, 1, 1);
    uint8_t loop_point[3];
    file->read(loop_point, 3, 1);
    this->loop_point = loop_point[0] | ((uint32_t)(loop_point[1]) << 8) | ((uint32_t)(loop_point[2]) << 16);
    file->read(loop_point, 3, 1);
    this->pcm_offset = loop_point[0] | ((uint32_t)(loop_point[1]) << 8) | ((uint32_t)(loop_point[2]) << 16);
    file->read(&fm_mask, 1, 1);
    file->read(loop_point, 2, 1);
    this->psg_channel_mask = loop_point[0] | ((uint16_t)(loop_point[1]) << 8);
    file->read(loop_point, 2, 1);
    this->tick_rate = loop_point[0] | ((uint16_t)(loop_point[1]) << 8);
    file->read(loop_point, 2, 1); // Reserved.
    music_data_start = file->get_pos();
    while (true) {
        ZsmCommand cmd = get_command();
        if (cmd.id == ZsmEOF) {
            break;
        }
    }
    music_data_len = file->get_pos();
    switch_stream(0);
}
extern SDL_AudioSpec obtained;
void ZsmBackend::switch_stream(int idx) {
    psg_reset();
    audio_close();
    audio_init(NULL, 16);
    spec = obtained;
}
void ZsmBackend::cleanup() {
    audio_close();
    delete file;
    file = nullptr;
}
size_t ZsmBackend::render(void *buf, size_t maxlen) {
    size_t sample_type_len = size_of_sample_type(spec.format);
    maxlen /= sample_type_len;
    double prevTicks = ticks;
    double delta = (double)(maxlen) / (double)(spec.freq);
    double deltaTicks = delta / (double)(tick_rate);
    ticks += deltaTicks;
    double clocks = delta * (double)(8000000);
    for (size_t i = 0; i < (size_t)(ticks - prevTicks); i++) {
        double deltaClocks = (double)(tick_rate) * (double)(8000000);
        clocks -= deltaClocks;
        if (clocks < 0) {
            break;
        }
        while (true) {
            ZsmCommand cmd = get_command();
            bool tick_end = false;
            if (delayTicks > 0.0) {
                delayTicks -= 1.0 / double(tick_rate);
                break;
            }
            switch (cmd.id) {
                case ZsmEOF: {
                    seek_internal((double)(loop_point) / (double)(tick_rate));
                } break;
                case PsgWrite: {
                    psg_writereg(cmd.psg_write.reg, cmd.psg_write.val);
                } break;
                case FmWrite: {
                    for (uint8_t i = 0; i < cmd.fm_write.len; i++) {
                        YM_write_reg(cmd.fm_write.regs[i].reg, cmd.fm_write.regs[i].val);
                    }
                } break;
                case Delay: {
                    delayTicks = cmd.delay;
                    tick_end = true;
                } break;
                case ExtCmd: {
                    // Nothing handled yet.
                } break;
            }
            if (tick_end) break;
        }
        audio_step((int)(clocks));
    }
    audio_render();
    maxlen *= sample_type_len;
    if (audio_buf.size() < maxlen) {
        size_t oldlen = audio_buf.size();
        audio_buf.resize(audio_buf.size() + spec.size);
        audio_callback(nullptr, (Uint8*)(audio_buf.data() + oldlen), spec.size);
    }
    memcpy(audio_buf.data(), buf, maxlen);
    memmove(audio_buf.data(), audio_buf.data() + maxlen, audio_buf.size() - maxlen);
    audio_buf.resize(audio_buf.size() - maxlen);
    return maxlen;
}
ZsmCommand ZsmBackend::get_command() {
    ZsmCommandId cmdid;
    uint8_t cmd_byte;
    file->read(&cmd_byte, 1, 1);
    if (cmd_byte == 0x80) {
        cmdid = ZsmEOF;
    } else {
        if ((cmd_byte & 0b11000000) == 0) {
            cmdid = PsgWrite;
        } else if ((cmd_byte & 0b11000000) == 0b01) {
            if (cmd_byte == 0b01000000) {
                cmdid = ExtCmd;
            } else {
                cmdid = FmWrite;
            }
        } else {
            cmdid = Delay;
        }
    }
    ZsmCommand output;
    output.id = cmdid;
    if (cmdid == ZsmEOF) {
        return output;
    } else if (cmdid == PsgWrite) {
        uint8_t value;
        file->read(&value, 1, 1);
        output.psg_write.reg = cmd_byte & 0x3F;
        output.psg_write.val = value;
    } else if (cmdid == FmWrite) {
        uint8_t value[2];
        uint8_t pairs = cmd_byte & 0b111111;
        output.fm_write.len = pairs;
        output.fm_write.regs = (reg_pair*)malloc((sizeof(uint8_t)*2)*pairs);
        for (uint8_t i = 0; i < pairs; i++) {
            output.fm_write.regs[i].reg = value[0];
            output.fm_write.regs[i].val = value[1];
            file->read(value, 2, 1);
        }
    } else if (cmdid == ExtCmd) {
        uint8_t ext_cmd_byte;
        file->read(&ext_cmd_byte, 1, 1);
        uint8_t bytes = ext_cmd_byte & 0x3F;
        uint8_t ch = ext_cmd_byte >> 6;
        output.extcmd.channel = ch;
        output.extcmd.bytes = bytes;
        if (ch == 1) {
            output.extcmd.expansion.write_bytes = (uint8_t*)malloc(bytes - 2);
        } else {
            output.extcmd.pcm = (uint8_t*)malloc(bytes); // Handles all other cases due to them being in a union, and each having the same type.
        }
        for (size_t i = 0; i < bytes; i++) {
            uint8_t byte;
            file->read(&byte, 1, 1);
            switch (ch) {
                case 0: {
                    output.extcmd.pcm[i] = byte;
                } break;
                case 1: {
                    if (i == 0) {
                        output.extcmd.expansion.chip_id = byte;
                    } else if (i == 1) {
                        output.extcmd.expansion.writes = byte;
                    } else {
                        output.extcmd.expansion.write_bytes[i - 2] = byte;
                    }
                } break;
                case 2: {
                    output.extcmd.sync[i] = byte;
                } break;
                case 3: {
                    output.extcmd.custom[i] = byte;
                } break;
            }
        }
    }
    return output;
}
ZsmCommand::~ZsmCommand() {
    switch (id) {
        case ExtCmd: {
            if (extcmd.channel == 1) {
                free(extcmd.expansion.write_bytes);
            } else {
                free(extcmd.pcm);
            }
        } break;
        case FmWrite: {
            free(fm_write.regs);
        }
    }
}
void ZsmBackend::seek_internal(double position) {
    double ticks = 0;
    file->seek(music_data_start, SeekType::SET);
    while (ticks < position) {
        ZsmCommand cmd = get_command();
        if (cmd.id == ZsmEOF) {
            file->seek(music_data_start, SeekType::SET);
            break;
        } else if (cmd.id == Delay) {
            ticks += (double)(cmd.delay) / (double)(tick_rate);
        }
    }
    this->position = position;
}
void ZsmBackend::seek(double position) {
    seek_internal(position);
}
double ZsmBackend::get_position() {
    return position;
}
int ZsmBackend::get_stream_idx() {
    return 0;
}