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Names the magic constants.

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This commit is contained in:
Thomas Harte 2018-04-08 10:35:07 -04:00
parent 3821679efd
commit 865c47a1ac
1 changed files with 20 additions and 7 deletions
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27
Machines/ZX8081/Video.cpp
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@ -10,6 +10,19 @@
using namespace ZX8081;
namespace {
/*!
The number of bytes of PCM data to allocate at once; if/when more are required,
the class will simply allocate another batch.
*/
const std::size_t StandardAllocationSize = 40;
/// The amount of time a byte takes to output.
const std::size_t HalfCyclesPerByte = 8;
}
Video::Video() :
crt_(new Outputs::CRT::CRT(207 * 2, 1, Outputs::CRT::DisplayType::PAL50, 1)) {
@ -46,10 +59,10 @@ void Video::flush(bool next_sync) {
if(line_data_) {
// If there is output data queued, output it either if it's being interrupted by
// sync, or if we're past its end anyway. Otherwise let it be.
unsigned int data_length = static_cast<unsigned int>(line_data_pointer_ - line_data_) * 8;
unsigned int data_length = static_cast<unsigned int>(line_data_pointer_ - line_data_) * HalfCyclesPerByte;
if(data_length < cycles_since_update_ || next_sync) {
unsigned int output_length = std::min(data_length, cycles_since_update_);
crt_->output_data(output_length, 8);
crt_->output_data(output_length, HalfCyclesPerByte);
line_data_pointer_ = line_data_ = nullptr;
cycles_since_update_ -= output_length;
} else return;
@ -80,16 +93,16 @@ void Video::output_byte(uint8_t byte) {
// Grab a buffer if one isn't already available.
if(!line_data_) {
line_data_pointer_ = line_data_ = crt_->allocate_write_area(40);
line_data_pointer_ = line_data_ = crt_->allocate_write_area(StandardAllocationSize);
}
// If a buffer was obtained, serialise the new pixels.
if(line_data_) {
// If the buffer is full, output it now and obtain a new one
if(line_data_pointer_ - line_data_ == 40) {
crt_->output_data(40, 8);
cycles_since_update_ -= 320;
line_data_pointer_ = line_data_ = crt_->allocate_write_area(40);
if(line_data_pointer_ - line_data_ == StandardAllocationSize) {
crt_->output_data(StandardAllocationSize, HalfCyclesPerByte);
cycles_since_update_ -= StandardAllocationSize * HalfCyclesPerByte;
line_data_pointer_ = line_data_ = crt_->allocate_write_area(StandardAllocationSize);
if(!line_data_) return;
}