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401 lines
14 KiB
C++
401 lines
14 KiB
C++
//
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// BufferingScanTarget.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 22/07/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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#include "BufferingScanTarget.hpp"
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#include <cassert>
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#include <cstring>
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#define TextureAddressGetY(v) uint16_t((v) >> 11)
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#define TextureAddressGetX(v) uint16_t((v) & 0x7ff)
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#define TextureSub(a, b) (((a) - (b)) & 0x3fffff)
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#define TextureAddress(x, y) (((y) << 11) | (x))
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using namespace Outputs::Display;
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BufferingScanTarget::BufferingScanTarget() {
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// Ensure proper initialisation of the two atomic pointer sets.
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read_pointers_.store(write_pointers_, std::memory_order::memory_order_relaxed);
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submit_pointers_.store(write_pointers_, std::memory_order::memory_order_relaxed);
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// Establish initial state for is_updating_.
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is_updating_.clear(std::memory_order::memory_order_relaxed);
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}
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// MARK: - Producer; pixel data.
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uint8_t *BufferingScanTarget::begin_data(size_t required_length, size_t required_alignment) {
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assert(required_alignment);
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// Acquire the standard producer lock, nominally over write_pointers_.
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std::lock_guard lock_guard(producer_mutex_);
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// If allocation has already failed on this line, continue the trend.
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if(allocation_has_failed_) return nullptr;
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// If there isn't yet a write area or data size then mark allocation as failed and finish.
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if(!write_area_ || !data_type_size_) {
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allocation_has_failed_ = true;
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return nullptr;
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}
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// Determine where the proposed write area would start and end.
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uint16_t output_y = TextureAddressGetY(write_pointers_.write_area);
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uint16_t aligned_start_x = TextureAddressGetX(write_pointers_.write_area & 0xffff) + 1;
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aligned_start_x += uint16_t((required_alignment - aligned_start_x%required_alignment)%required_alignment);
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uint16_t end_x = aligned_start_x + uint16_t(1 + required_length);
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if(end_x > WriteAreaWidth) {
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output_y = (output_y + 1) % WriteAreaHeight;
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aligned_start_x = uint16_t(required_alignment);
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end_x = aligned_start_x + uint16_t(1 + required_length);
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}
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// Check whether that steps over the read pointer; if so then the final address will be closer
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// to the write pointer than the old.
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const auto end_address = TextureAddress(end_x, output_y);
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const auto read_pointers = read_pointers_.load(std::memory_order::memory_order_relaxed);
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const auto end_distance = TextureSub(end_address, read_pointers.write_area);
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const auto previous_distance = TextureSub(write_pointers_.write_area, read_pointers.write_area);
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// Perform a quick sanity check.
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assert(end_distance >= 0);
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assert(previous_distance >= 0);
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// If allocating this would somehow make the write pointer back away from the read pointer,
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// there must not be enough space left.
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if(end_distance < previous_distance) {
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allocation_has_failed_ = true;
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return nullptr;
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}
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// Everything checks out, note expectation of a future end_data and return the pointer.
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assert(!data_is_allocated_);
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data_is_allocated_ = true;
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vended_write_area_pointer_ = write_pointers_.write_area = TextureAddress(aligned_start_x, output_y);
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assert(write_pointers_.write_area >= 1 && ((size_t(write_pointers_.write_area) + required_length + 1) * data_type_size_) <= WriteAreaWidth*WriteAreaHeight*data_type_size_);
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return &write_area_[size_t(write_pointers_.write_area) * data_type_size_];
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// Note state at exit:
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// write_pointers_.write_area points to the first pixel the client is expected to draw to.
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}
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template <typename DataUnit> void BufferingScanTarget::end_data(size_t actual_length) {
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// Bookend the start and end of the new data, to safeguard for precision errors in sampling.
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DataUnit *const sized_write_area = &reinterpret_cast<DataUnit *>(write_area_)[write_pointers_.write_area];
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sized_write_area[-1] = sized_write_area[0];
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sized_write_area[actual_length] = sized_write_area[actual_length - 1];
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}
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void BufferingScanTarget::end_data(size_t actual_length) {
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// Acquire the producer lock.
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std::lock_guard lock_guard(producer_mutex_);
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// Do nothing if no data write is actually ongoing.
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if(!data_is_allocated_) return;
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data_is_allocated_ = false;
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// Check for other allocation failures.
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if(allocation_has_failed_) return;
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// Apply necessary bookends.
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switch(data_type_size_) {
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default: assert(false);
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case 0:
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// This just means that modals haven't been grabbed yet. So it's not
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// a valid data type size, but it is a value that might legitimately
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// be seen here.
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break;
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case 1: end_data<uint8_t>(actual_length); break;
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case 2: end_data<uint16_t>(actual_length); break;
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case 4: end_data<uint32_t>(actual_length); break;
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}
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// Advance to the end of the current run.
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write_pointers_.write_area += actual_length + 1;
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// The write area was allocated in the knowledge that there's sufficient
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// distance left on the current line, but there's a risk of exactly filling
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// the final line, in which case this should wrap back to 0.
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write_pointers_.write_area %= WriteAreaWidth*WriteAreaHeight;
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}
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// MARK: - Producer; scans.
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Outputs::Display::ScanTarget::Scan *BufferingScanTarget::begin_scan() {
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std::lock_guard lock_guard(producer_mutex_);
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// If there's already an allocation failure on this line, do no work.
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if(allocation_has_failed_) {
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vended_scan_ = nullptr;
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return nullptr;
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}
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const auto result = &scan_buffer_[write_pointers_.scan];
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const auto read_pointers = read_pointers_.load(std::memory_order::memory_order_relaxed);
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// Advance the pointer.
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const auto next_write_pointer = decltype(write_pointers_.scan)((write_pointers_.scan + 1) % scan_buffer_size_);
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// Check whether that's too many.
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if(next_write_pointer == read_pointers.scan) {
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allocation_has_failed_ = true;
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vended_scan_ = nullptr;
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return nullptr;
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}
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write_pointers_.scan = next_write_pointer;
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++provided_scans_;
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// Fill in extra OpenGL-specific details.
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result->line = write_pointers_.line;
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vended_scan_ = result;
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#ifndef NDEBUG
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assert(!scan_is_ongoing_);
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scan_is_ongoing_ = true;
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#endif
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return &result->scan;
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}
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void BufferingScanTarget::end_scan() {
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std::lock_guard lock_guard(producer_mutex_);
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#ifndef NDEBUG
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assert(scan_is_ongoing_);
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scan_is_ongoing_ = false;
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#endif
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// Complete the scan only if one is afoot.
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if(vended_scan_) {
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vended_scan_->data_y = TextureAddressGetY(vended_write_area_pointer_);
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vended_scan_->line = write_pointers_.line;
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vended_scan_->scan.end_points[0].data_offset += TextureAddressGetX(vended_write_area_pointer_);
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vended_scan_->scan.end_points[1].data_offset += TextureAddressGetX(vended_write_area_pointer_);
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vended_scan_ = nullptr;
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}
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}
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// MARK: - Producer; lines.
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void BufferingScanTarget::announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t composite_amplitude) {
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std::lock_guard lock_guard(producer_mutex_);
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// Forward the event to the display metrics tracker.
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display_metrics_.announce_event(event);
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if(event == ScanTarget::Event::EndVerticalRetrace) {
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// The previous-frame-is-complete flag is subject to a two-slot queue because
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// measurement for *this* frame needs to begin now, meaning that the previous
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// result needs to be put somewhere — it'll be attached to the first successful
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// line output, whenever that comes.
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is_first_in_frame_ = true;
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previous_frame_was_complete_ = frame_is_complete_;
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frame_is_complete_ = true;
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}
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// Proceed from here only if a change in visibility has occurred.
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if(output_is_visible_ == is_visible) return;
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output_is_visible_ = is_visible;
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#ifndef NDEBUG
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assert(!scan_is_ongoing_);
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#endif
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if(is_visible) {
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const auto read_pointers = read_pointers_.load(std::memory_order::memory_order_relaxed);
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// Attempt to allocate a new line, noting allocation success or failure.
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const auto next_line = uint16_t((write_pointers_.line + 1) % line_buffer_size_);
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allocation_has_failed_ = next_line == read_pointers.line;
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if(!allocation_has_failed_) {
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// If there was space for a new line, establish its start and reset the count of provided scans.
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Line &active_line = line_buffer_[size_t(write_pointers_.line)];
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active_line.end_points[0].x = location.x;
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active_line.end_points[0].y = location.y;
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active_line.end_points[0].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
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active_line.end_points[0].composite_angle = location.composite_angle;
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active_line.line = write_pointers_.line;
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active_line.composite_amplitude = composite_amplitude;
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provided_scans_ = 0;
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}
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} else {
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// Commit the most recent line only if any scans fell on it and all allocation was successful.
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if(!allocation_has_failed_ && provided_scans_) {
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const auto submit_pointers = submit_pointers_.load(std::memory_order::memory_order_relaxed);
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// Store metadata.
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LineMetadata &metadata = line_metadata_buffer_[size_t(write_pointers_.line)];
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metadata.is_first_in_frame = is_first_in_frame_;
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metadata.previous_frame_was_complete = previous_frame_was_complete_;
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metadata.first_scan = submit_pointers.scan;
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is_first_in_frame_ = false;
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// Sanity check.
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assert(((metadata.first_scan + size_t(provided_scans_)) % scan_buffer_size_) == write_pointers_.scan);
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// Store actual line data.
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Line &active_line = line_buffer_[size_t(write_pointers_.line)];
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active_line.end_points[1].x = location.x;
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active_line.end_points[1].y = location.y;
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active_line.end_points[1].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
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active_line.end_points[1].composite_angle = location.composite_angle;
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// Advance the line pointer.
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write_pointers_.line = uint16_t((write_pointers_.line + 1) % line_buffer_size_);
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// Update the submit pointers with all lines, scans and data written during this line.
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std::atomic_thread_fence(std::memory_order::memory_order_release);
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submit_pointers_.store(write_pointers_, std::memory_order::memory_order_release);
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} else {
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// Something failed, or there was nothing on the line anyway, so reset all pointers to where they
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// were before this line. Mark frame as incomplete if this was an allocation failure.
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write_pointers_ = submit_pointers_.load(std::memory_order::memory_order_relaxed);
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frame_is_complete_ &= !allocation_has_failed_;
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}
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// Don't permit anything to be allocated on invisible areas.
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allocation_has_failed_ = true;
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}
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}
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// MARK: - Producer; other state.
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void BufferingScanTarget::will_change_owner() {
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std::lock_guard lock_guard(producer_mutex_);
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allocation_has_failed_ = true;
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vended_scan_ = nullptr;
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#ifdef DEBUG
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data_is_allocated_ = false;
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#endif
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}
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const Outputs::Display::Metrics &BufferingScanTarget::display_metrics() {
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return display_metrics_;
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}
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void BufferingScanTarget::set_write_area(uint8_t *base) {
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std::lock_guard lock_guard(producer_mutex_);
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write_area_ = base;
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write_pointers_ = submit_pointers_ = read_pointers_ = PointerSet();
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allocation_has_failed_ = true;
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vended_scan_ = nullptr;
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}
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size_t BufferingScanTarget::write_area_data_size() const {
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// TODO: can I guarantee this is safe without requiring that set_write_area
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// be within an @c perform block?
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return data_type_size_;
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}
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void BufferingScanTarget::set_modals(Modals modals) {
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perform([=] {
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modals_ = modals;
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modals_are_dirty_.store(true, std::memory_order::memory_order_relaxed);
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});
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}
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// MARK: - Consumer.
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BufferingScanTarget::OutputArea BufferingScanTarget::get_output_area() {
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// The area to draw is that between the read pointers, representing wherever reading
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// last stopped, and the submit pointers, representing all the new data that has been
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// cleared for submission.
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const auto submit_pointers = submit_pointers_.load(std::memory_order::memory_order_acquire);
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const auto read_ahead_pointers = read_ahead_pointers_.load(std::memory_order::memory_order_relaxed);
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std::atomic_thread_fence(std::memory_order::memory_order_acquire);
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OutputArea area;
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area.start.line = read_ahead_pointers.line;
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area.end.line = submit_pointers.line;
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area.start.scan = read_ahead_pointers.scan;
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area.end.scan = submit_pointers.scan;
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area.start.write_area_x = TextureAddressGetX(read_ahead_pointers.write_area);
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area.start.write_area_y = TextureAddressGetY(read_ahead_pointers.write_area);
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area.end.write_area_x = TextureAddressGetX(submit_pointers.write_area);
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area.end.write_area_y = TextureAddressGetY(submit_pointers.write_area);
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// Update the read-ahead pointers.
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read_ahead_pointers_.store(submit_pointers, std::memory_order::memory_order_relaxed);
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#ifndef NDEBUG
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area.counter = output_area_counter_;
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++output_area_counter_;
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#endif
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return area;
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}
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void BufferingScanTarget::complete_output_area(const OutputArea &area) {
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// TODO: check that this is the expected next area if in DEBUG mode.
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PointerSet new_read_pointers;
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new_read_pointers.line = uint16_t(area.end.line);
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new_read_pointers.scan = uint16_t(area.end.scan);
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new_read_pointers.write_area = TextureAddress(area.end.write_area_x, area.end.write_area_y);
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read_pointers_.store(new_read_pointers, std::memory_order::memory_order_relaxed);
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#ifndef NDEBUG
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// This will fire if the caller is announcing completed output areas out of order.
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assert(area.counter == output_area_next_returned_);
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++output_area_next_returned_;
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#endif
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}
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void BufferingScanTarget::perform(const std::function<void(void)> &function) {
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while(is_updating_.test_and_set(std::memory_order_acquire));
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function();
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is_updating_.clear(std::memory_order_release);
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}
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void BufferingScanTarget::set_scan_buffer(Scan *buffer, size_t size) {
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scan_buffer_ = buffer;
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scan_buffer_size_ = size;
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}
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void BufferingScanTarget::set_line_buffer(Line *line_buffer, LineMetadata *metadata_buffer, size_t size) {
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line_buffer_ = line_buffer;
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line_metadata_buffer_ = metadata_buffer;
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line_buffer_size_ = size;
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}
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const Outputs::Display::ScanTarget::Modals *BufferingScanTarget::new_modals() {
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const auto modals_are_dirty = modals_are_dirty_.load(std::memory_order::memory_order_relaxed);
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if(!modals_are_dirty) {
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return nullptr;
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}
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modals_are_dirty_.store(false, std::memory_order::memory_order_relaxed);
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// MAJOR SHARP EDGE HERE: assume that because the new_modals have been fetched then the caller will
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// now ensure their texture buffer is appropriate. They might provide a new pointer and might now.
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// But either way it's now appropriate to start treating the data size as implied by the data type.
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std::lock_guard lock_guard(producer_mutex_);
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data_type_size_ = Outputs::Display::size_for_data_type(modals_.input_data_type);
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assert((data_type_size_ == 1) || (data_type_size_ == 2) || (data_type_size_ == 4));
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return &modals_;
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}
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const Outputs::Display::ScanTarget::Modals &BufferingScanTarget::modals() const {
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return modals_;
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}
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bool BufferingScanTarget::has_new_modals() const {
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return modals_are_dirty_.load(std::memory_order::memory_order_relaxed);
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}
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