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278 lines
10 KiB
C++
278 lines
10 KiB
C++
//
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// BufferingScanTarget.hpp
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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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#ifndef BufferingScanTarget_hpp
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#define BufferingScanTarget_hpp
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#include "../ScanTarget.hpp"
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#include "../DisplayMetrics.hpp"
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#include <array>
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#include <atomic>
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#include <functional>
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#include <mutex>
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#include <vector>
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namespace Outputs::Display {
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/*!
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Provides basic thread-safe (hopefully) circular queues for any scan target that:
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* will store incoming Scans into a linear circular buffer and pack regions of
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incoming pixel data into a 2048x2048 2d texture;
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* will compose whole lines of content by partioning the Scans based on sync
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placement and then pasting together their content;
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* will process those lines as necessary to map from input format to whatever
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suits the display; and
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* will then output the lines.
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This buffer rejects new data when full.
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*/
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class BufferingScanTarget: public Outputs::Display::ScanTarget {
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public:
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/*! @returns The DisplayMetrics object that this ScanTarget has been providing with announcements and draw overages. */
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const Metrics &display_metrics();
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static constexpr int WriteAreaWidth = 2048;
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static constexpr int WriteAreaHeight = 2048;
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BufferingScanTarget();
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// This is included because it's assumed that scan targets will want to expose one.
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// It is the subclass's responsibility to post timings.
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Metrics display_metrics_;
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/// Extends the definition of a Scan to include two extra fields,
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/// completing this scan's source data and destination locations.
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struct Scan {
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Outputs::Display::ScanTarget::Scan scan;
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/// Stores the y coordinate for this scan's data within the write area texture.
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/// Use this plus the scan's endpoints' data_offsets to locate this data in 2d.
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/// Note that the data_offsets will have been adjusted to be relative to the line
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/// they fall within, not the data allocation.
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uint16_t data_y;
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/// Stores the y coordinate assigned to this scan within the intermediate buffers.
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/// Use this plus this scan's endpoints' x locations to determine where to composite
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/// this data for intermediate processing.
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uint16_t line;
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};
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/// Defines the boundaries of a complete line of video — a 2d start and end location,
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/// composite phase and amplitude (if relevant), the source line in the intermediate buffer
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/// plus the start and end offsets of the area that is visible from the intermediate buffer.
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struct Line {
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struct EndPoint {
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uint16_t x, y;
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int16_t composite_angle;
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uint16_t cycles_since_end_of_horizontal_retrace;
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} end_points[2];
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uint8_t composite_amplitude;
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uint16_t line;
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};
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/// Provides additional metadata about lines; this is separate because it's unlikely to be of
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/// interest to the GPU, unlike the fields in Line.
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struct LineMetadata {
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/// @c true if this line was the first drawn after vertical sync; @c false otherwise.
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bool is_first_in_frame;
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/// @c true if this line is the first in the frame and if every single piece of output
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/// from the previous frame was recorded; @c false otherwise. Data can be dropped
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/// from a frame if performance problems mean that the emulated machine is running
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/// more quickly than complete frames can be generated.
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bool previous_frame_was_complete;
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/// The index of the first scan that will appear on this line.
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size_t first_scan;
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};
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/// Sets the area of memory to use as a scan buffer.
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void set_scan_buffer(Scan *buffer, size_t size);
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/// Sets the area of memory to use as line and line metadata buffers.
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void set_line_buffer(Line *line_buffer, LineMetadata *metadata_buffer, size_t size);
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/// Sets a new base address for the texture.
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/// When called this will flush all existing data and load up the
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/// new data size.
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void set_write_area(uint8_t *base);
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/// @returns The number of bytes per input sample, as per the latest modals.
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size_t write_area_data_size() const;
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/// Defines a segment of data now ready for output, consisting of start and endpoints for:
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///
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/// (i) the region of the write area that has been modified; if the caller is using shared memory
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/// for the write area then it can ignore this information;
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///
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/// (ii) the number of scans that have been completed; and
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///
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/// (iii) the number of lines that have been completed.
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///
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/// New write areas and scans are exposed only upon completion of the corresponding lines.
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/// The values indicated by the start point are the first that should be drawn. Those indicated
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/// by the end point are one after the final that should be drawn.
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///
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/// So e.g. start.scan = 23, end.scan = 24 means draw a single scan, index 23.
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struct OutputArea {
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struct Endpoint {
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int write_area_x, write_area_y;
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size_t scan;
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size_t line;
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};
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Endpoint start, end;
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#ifndef NDEBUG
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size_t counter;
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#endif
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};
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/// Gets the current range of content that has been posted but not yet returned by
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/// a previous call to get_output_area().
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///
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/// Does not require the caller to be within a @c perform block.
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OutputArea get_output_area();
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/// Announces that the output area has now completed output, freeing up its memory for
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/// further modification.
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///
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/// It is the caller's responsibility to ensure that the areas passed to complete_output_area
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/// are those from get_output_area and are marked as completed in the same order that
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/// they were originally provided.
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///
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/// Does not require the caller to be within a @c perform block.
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void complete_output_area(const OutputArea &);
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/// Performs @c action ensuring that no other @c perform actions, or any
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/// change to modals, occurs simultaneously.
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void perform(const std::function<void(void)> &action);
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/// @returns new Modals if any have been set since the last call to get_new_modals().
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/// The caller must be within a @c perform block.
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const Modals *new_modals();
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/// @returns the current @c Modals.
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const Modals &modals() const;
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/// @returns @c true if new modals are available; @c false otherwise.
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///
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/// Safe to call from any thread.
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bool has_new_modals() const;
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private:
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// ScanTarget overrides.
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void set_modals(Modals) final;
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Outputs::Display::ScanTarget::Scan *begin_scan() final;
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void end_scan() final;
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uint8_t *begin_data(size_t required_length, size_t required_alignment) final;
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void end_data(size_t actual_length) final;
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void announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t colour_burst_amplitude) final;
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void will_change_owner() final;
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// Uses a texture to vend write areas.
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uint8_t *write_area_ = nullptr;
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size_t data_type_size_ = 0;
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// Tracks changes in raster visibility in order to populate
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// Lines and LineMetadatas.
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bool output_is_visible_ = false;
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// Track allocation failures.
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bool data_is_allocated_ = false;
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bool allocation_has_failed_ = false;
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// Ephemeral information for the begin/end functions.
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Scan *vended_scan_ = nullptr;
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int vended_write_area_pointer_ = 0;
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// Ephemeral state that helps in line composition.
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int provided_scans_ = 0;
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bool is_first_in_frame_ = true;
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bool frame_is_complete_ = true;
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bool previous_frame_was_complete_ = true;
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// By convention everything in the PointerSet points to the next instance
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// of whatever it is that will be used. So a client should start with whatever
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// is pointed to by the read pointers and carry until it gets to a value that
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// is equal to whatever is in the submit pointers.
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struct PointerSet {
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// This constructor is here to appease GCC's interpretation of
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// an ambiguity in the C++ standard; cf. https://stackoverflow.com/questions/17430377
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PointerSet() noexcept {}
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// Squeezing this struct into 64 bits makes the std::atomics more likely
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// to be lock free; they are under LLVM x86-64.
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// Points to the vended area in the write area texture.
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// The vended area is always preceded by a guard pixel, so a
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// sensible default construction is write_area = 1.
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int32_t write_area = 1;
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// Points into the scan buffer.
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uint16_t scan = 0;
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// Points into the line buffer.
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uint16_t line = 0;
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};
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/// A pointer to the final thing currently cleared for submission.
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std::atomic<PointerSet> submit_pointers_;
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/// A pointer to the first thing not yet submitted for display; this is
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/// atomic since it also acts as the buffer into which the write_pointers_
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/// may run and is therefore used by both producer and consumer.
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std::atomic<PointerSet> read_pointers_;
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std::atomic<PointerSet> read_ahead_pointers_;
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/// This is used as a spinlock to guard `perform` calls.
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std::atomic_flag is_updating_;
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/// A mutex for gettng access to anything the producer modifies — i.e. the write_pointers_,
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/// data_type_size_ and write_area_texture_, and all other state to do with capturing
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/// data, scans and lines.
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///
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/// This is almost never contended. The main collision is a user-prompted change of modals while the
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/// emulation thread is running.
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std::mutex producer_mutex_;
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/// A pointer to the next thing that should be provided to the caller for data.
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PointerSet write_pointers_;
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// The owner-supplied scan buffer and size.
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Scan *scan_buffer_ = nullptr;
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size_t scan_buffer_size_ = 0;
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// The owner-supplied line buffer and size.
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Line *line_buffer_ = nullptr;
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LineMetadata *line_metadata_buffer_ = nullptr;
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size_t line_buffer_size_ = 0;
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// Current modals and whether they've yet been returned
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// from a call to @c get_new_modals.
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Modals modals_;
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std::atomic<bool> modals_are_dirty_ = false;
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// Provides a per-data size implementation of end_data; a previous
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// implementation used blind memcpy and that turned into something
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// of a profiling hot spot.
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template <typename DataUnit> void end_data(size_t actual_length);
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#ifndef NDEBUG
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// Debug features; these amount to API validation.
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bool scan_is_ongoing_ = false;
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size_t output_area_counter_ = 0;
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size_t output_area_next_returned_ = 0;
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#endif
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};
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}
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#endif /* BufferingScanTarget_hpp */
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