Pulls the BufferingScanTarget into a separate file.

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -786,6 +786,8 @@
 		4BC1317B2346DF2B00E4FF3D /* MSA.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC131782346DF2B00E4FF3D /* MSA.cpp */; };
 		4BC23A2C2467600F001A6030 /* OPLL.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC23A2B2467600E001A6030 /* OPLL.cpp */; };
 		4BC23A2D2467600F001A6030 /* OPLL.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC23A2B2467600E001A6030 /* OPLL.cpp */; };
+		4BC3C67C24C9230F0027BF76 /* BufferingScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC3C67A24C9230F0027BF76 /* BufferingScanTarget.cpp */; };
+		4BC3C67D24C9230F0027BF76 /* BufferingScanTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC3C67A24C9230F0027BF76 /* BufferingScanTarget.cpp */; };
 		4BC57CD92436A62900FBC404 /* State.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC57CD82436A62900FBC404 /* State.cpp */; };
 		4BC57CDA2436A62900FBC404 /* State.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC57CD82436A62900FBC404 /* State.cpp */; };
 		4BC5C3E022C994CD00795658 /* 68000MoveTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4BC5C3DF22C994CC00795658 /* 68000MoveTests.mm */; };
@@ -1668,6 +1670,8 @@
 		4BC23A292467600E001A6030 /* OPLBase.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = OPLBase.hpp; sourceTree = "<group>"; };
 		4BC23A2A2467600E001A6030 /* EnvelopeGenerator.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = EnvelopeGenerator.hpp; sourceTree = "<group>"; };
 		4BC23A2B2467600E001A6030 /* OPLL.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = OPLL.cpp; sourceTree = "<group>"; };
+		4BC3C67A24C9230F0027BF76 /* BufferingScanTarget.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = BufferingScanTarget.cpp; path = ../../Outputs/ScanTargets/BufferingScanTarget.cpp; sourceTree = "<group>"; };
+		4BC3C67B24C9230F0027BF76 /* BufferingScanTarget.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; name = BufferingScanTarget.hpp; path = ../../Outputs/ScanTargets/BufferingScanTarget.hpp; sourceTree = "<group>"; };
 		4BC57CD2243427C700FBC404 /* AudioProducer.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = AudioProducer.hpp; sourceTree = "<group>"; };
 		4BC57CD32434282000FBC404 /* TimedMachine.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TimedMachine.hpp; sourceTree = "<group>"; };
 		4BC57CD424342E0600FBC404 /* MachineTypes.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = MachineTypes.hpp; sourceTree = "<group>"; };
@@ -3307,6 +3311,8 @@
 		4BB73E951B587A5100552FC2 = {
 			isa = PBXGroup;
 			children = (
+				4BC3C67A24C9230F0027BF76 /* BufferingScanTarget.cpp */,
+				4BC3C67B24C9230F0027BF76 /* BufferingScanTarget.hpp */,
 				4BC76E6A1C98F43700E6EF73 /* Accelerate.framework */,
 				4B51F70820A521D700AFA2C1 /* Activity */,
 				4B8944E2201967B4007DE474 /* Analyser */,
@@ -4485,6 +4491,7 @@
 				4BEBFB522002DB30000708CC /* DiskROM.cpp in Sources */,
 				4BC23A2D2467600F001A6030 /* OPLL.cpp in Sources */,
 				4B055AA11FAE85DA0060FFFF /* OricMFMDSK.cpp in Sources */,
+				4BC3C67D24C9230F0027BF76 /* BufferingScanTarget.cpp in Sources */,
 				4B0ACC2923775819008902D0 /* DMAController.cpp in Sources */,
 				4B055A951FAE85BB0060FFFF /* BitReverse.cpp in Sources */,
 				4B055ACE1FAE9B030060FFFF /* Plus3.cpp in Sources */,
@@ -4631,6 +4638,7 @@
 				4B3BF5B01F146265005B6C36 /* CSW.cpp in Sources */,
 				4BCE0060227D39AB000CA200 /* Video.cpp in Sources */,
 				4B0ACC2E23775819008902D0 /* TIA.cpp in Sources */,
+				4BC3C67C24C9230F0027BF76 /* BufferingScanTarget.cpp in Sources */,
 				4B74CF85231370BC00500CE8 /* MacintoshVolume.cpp in Sources */,
 				4B4518A51F75FD1C00926311 /* SSD.cpp in Sources */,
 				4B55CE5F1C3B7D960093A61B /* MachineDocument.swift in Sources */,

Outputs/OpenGL/ScanTarget.cpp

@@ -40,11 +40,6 @@ constexpr GLenum QAMChromaTextureUnit = GL_TEXTURE2;
 /// The texture unit that contains the current display.
 constexpr GLenum AccumulationTextureUnit = GL_TEXTURE3;
 
-#define TextureAddress(x, y)	(((y) << 11) | (x))
-#define TextureAddressGetY(v)	uint16_t((v) >> 11)
-#define TextureAddressGetX(v)	uint16_t((v) & 0x7ff)
-#define TextureSub(a, b)		(((a) - (b)) & 0x3fffff)
-
 constexpr GLint internalFormatForDepth(std::size_t depth) {
 	switch(depth) {
 		default: return GL_FALSE;
@@ -119,231 +114,6 @@ void ScanTarget::set_target_framebuffer(GLuint target_framebuffer) {
 	is_updating_.clear();
 }
 
-void BufferingScanTarget::set_modals(Modals modals) {
-	// Don't change the modals while drawing is ongoing; a previous set might be
-	// in the process of being established.
-	while(is_updating_.test_and_set());
-	modals_ = modals;
-	modals_are_dirty_ = true;
-	is_updating_.clear();
-}
-
-Outputs::Display::ScanTarget::Scan *BufferingScanTarget::begin_scan() {
-	if(allocation_has_failed_) return nullptr;
-
-	std::lock_guard lock_guard(write_pointers_mutex_);
-
-	const auto result = &scan_buffer_[write_pointers_.scan_buffer];
-	const auto read_pointers = read_pointers_.load();
-
-	// Advance the pointer.
-	const auto next_write_pointer = decltype(write_pointers_.scan_buffer)((write_pointers_.scan_buffer + 1) % scan_buffer_.size());
-
-	// Check whether that's too many.
-	if(next_write_pointer == read_pointers.scan_buffer) {
-		allocation_has_failed_ = true;
-		return nullptr;
-	}
-	write_pointers_.scan_buffer = next_write_pointer;
-	++provided_scans_;
-
-	// Fill in extra OpenGL-specific details.
-	result->line = write_pointers_.line;
-
-	vended_scan_ = result;
-	return &result->scan;
-}
-
-void BufferingScanTarget::end_scan() {
-	if(vended_scan_) {
-		std::lock_guard lock_guard(write_pointers_mutex_);
-		vended_scan_->data_y = TextureAddressGetY(vended_write_area_pointer_);
-		vended_scan_->line = write_pointers_.line;
-		vended_scan_->scan.end_points[0].data_offset += TextureAddressGetX(vended_write_area_pointer_);
-		vended_scan_->scan.end_points[1].data_offset += TextureAddressGetX(vended_write_area_pointer_);
-
-#ifdef LOG_SCANS
-		if(vended_scan_->scan.composite_amplitude) {
-			std::cout << "S: ";
-			std::cout << vended_scan_->scan.end_points[0].composite_angle << "/" << vended_scan_->scan.end_points[0].data_offset << "/" << vended_scan_->scan.end_points[0].cycles_since_end_of_horizontal_retrace << " -> ";
-			std::cout << vended_scan_->scan.end_points[1].composite_angle << "/" << vended_scan_->scan.end_points[1].data_offset << "/" << vended_scan_->scan.end_points[1].cycles_since_end_of_horizontal_retrace << " => ";
-			std::cout << double(vended_scan_->scan.end_points[1].composite_angle - vended_scan_->scan.end_points[0].composite_angle) / (double(vended_scan_->scan.end_points[1].data_offset - vended_scan_->scan.end_points[0].data_offset) * 64.0f) << "/";
-			std::cout << double(vended_scan_->scan.end_points[1].composite_angle - vended_scan_->scan.end_points[0].composite_angle) / (double(vended_scan_->scan.end_points[1].cycles_since_end_of_horizontal_retrace - vended_scan_->scan.end_points[0].cycles_since_end_of_horizontal_retrace) * 64.0f);
-			std::cout << std::endl;
-		}
-#endif
-	}
-	vended_scan_ = nullptr;
-}
-
-uint8_t *BufferingScanTarget::begin_data(size_t required_length, size_t required_alignment) {
-	assert(required_alignment);
-
-	if(allocation_has_failed_) return nullptr;
-
-	std::lock_guard lock_guard(write_pointers_mutex_);
-	if(write_area_texture_.empty()) {
-		allocation_has_failed_ = true;
-		return nullptr;
-	}
-
-	// Determine where the proposed write area would start and end.
-	uint16_t output_y = TextureAddressGetY(write_pointers_.write_area);
-
-	uint16_t aligned_start_x = TextureAddressGetX(write_pointers_.write_area & 0xffff) + 1;
-	aligned_start_x += uint16_t((required_alignment - aligned_start_x%required_alignment)%required_alignment);
-
-	uint16_t end_x = aligned_start_x + uint16_t(1 + required_length);
-
-	if(end_x > WriteAreaWidth) {
-		output_y = (output_y + 1) % WriteAreaHeight;
-		aligned_start_x = uint16_t(required_alignment);
-		end_x = aligned_start_x + uint16_t(1 + required_length);
-	}
-
-	// Check whether that steps over the read pointer.
-	const auto end_address = TextureAddress(end_x, output_y);
-	const auto read_pointers = read_pointers_.load();
-
-	const auto end_distance = TextureSub(end_address, read_pointers.write_area);
-	const auto previous_distance = TextureSub(write_pointers_.write_area, read_pointers.write_area);
-
-	// If allocating this would somehow make the write pointer back away from the read pointer,
-	// there must not be enough space left.
-	if(end_distance < previous_distance) {
-		allocation_has_failed_ = true;
-		return nullptr;
-	}
-
-	// Everything checks out, note expectation of a future end_data and return the pointer.
-	data_is_allocated_ = true;
-	vended_write_area_pointer_ = write_pointers_.write_area = TextureAddress(aligned_start_x, output_y);
-
-	assert(write_pointers_.write_area >= 1 && ((size_t(write_pointers_.write_area) + required_length + 1) * data_type_size_) <= write_area_texture_.size());
-	return &write_area_texture_[size_t(write_pointers_.write_area) * data_type_size_];
-
-	// Note state at exit:
-	//		write_pointers_.write_area points to the first pixel the client is expected to draw to.
-}
-
-void BufferingScanTarget::end_data(size_t actual_length) {
-	if(allocation_has_failed_ || !data_is_allocated_) return;
-
-	std::lock_guard lock_guard(write_pointers_mutex_);
-
-	// Bookend the start of the new data, to safeguard for precision errors in sampling.
-	memcpy(
-		&write_area_texture_[size_t(write_pointers_.write_area - 1) * data_type_size_],
-		&write_area_texture_[size_t(write_pointers_.write_area) * data_type_size_],
-		data_type_size_);
-
-	// Advance to the end of the current run.
-	write_pointers_.write_area += actual_length + 1;
-
-	// Also bookend the end.
-	memcpy(
-		&write_area_texture_[size_t(write_pointers_.write_area - 1) * data_type_size_],
-		&write_area_texture_[size_t(write_pointers_.write_area - 2) * data_type_size_],
-		data_type_size_);
-
-	// The write area was allocated in the knowledge that there's sufficient
-	// distance left on the current line, but there's a risk of exactly filling
-	// the final line, in which case this should wrap back to 0.
-	write_pointers_.write_area %= (write_area_texture_.size() / data_type_size_);
-
-	// Record that no further end_data calls are expected.
-	data_is_allocated_ = false;
-}
-
-void ScanTarget::will_change_owner() {
-	allocation_has_failed_ = true;
-	vended_scan_ = nullptr;
-}
-
-void BufferingScanTarget::announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t composite_amplitude) {
-	// Forward the event to the display metrics tracker.
-	display_metrics_.announce_event(event);
-
-	if(event == ScanTarget::Event::EndVerticalRetrace) {
-		// The previous-frame-is-complete flag is subject to a two-slot queue because
-		// measurement for *this* frame needs to begin now, meaning that the previous
-		// result needs to be put somewhere — it'll be attached to the first successful
-		// line output.
-		is_first_in_frame_ = true;
-		previous_frame_was_complete_ = frame_is_complete_;
-		frame_is_complete_ = true;
-	}
-
-	if(output_is_visible_ == is_visible) return;
-	if(is_visible) {
-		const auto read_pointers = read_pointers_.load();
-		std::lock_guard lock_guard(write_pointers_mutex_);
-
-		// Commit the most recent line only if any scans fell on it.
-		// Otherwise there's no point outputting it, it'll contribute nothing.
-		if(provided_scans_) {
-			// Store metadata if concluding a previous line.
-			if(active_line_) {
-				line_metadata_buffer_[size_t(write_pointers_.line)].is_first_in_frame = is_first_in_frame_;
-				line_metadata_buffer_[size_t(write_pointers_.line)].previous_frame_was_complete = previous_frame_was_complete_;
-				is_first_in_frame_ = false;
-			}
-
-			// Attempt to allocate a new line; note allocation failure if necessary.
-			const auto next_line = uint16_t((write_pointers_.line + 1) % LineBufferHeight);
-			if(next_line == read_pointers.line) {
-				allocation_has_failed_ = true;
-				active_line_ = nullptr;
-			} else {
-				write_pointers_.line = next_line;
-				active_line_ = &line_buffer_[size_t(write_pointers_.line)];
-			}
-			provided_scans_ = 0;
-		}
-
-		if(active_line_) {
-			active_line_->end_points[0].x = location.x;
-			active_line_->end_points[0].y = location.y;
-			active_line_->end_points[0].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
-			active_line_->end_points[0].composite_angle = location.composite_angle;
-			active_line_->line = write_pointers_.line;
-			active_line_->composite_amplitude = composite_amplitude;
-		}
-	} else {
-		if(active_line_) {
-			// A successfully-allocated line is ending.
-			active_line_->end_points[1].x = location.x;
-			active_line_->end_points[1].y = location.y;
-			active_line_->end_points[1].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
-			active_line_->end_points[1].composite_angle = location.composite_angle;
-
-#ifdef LOG_LINES
-			if(active_line_->composite_amplitude) {
-				std::cout << "L: ";
-				std::cout << active_line_->end_points[0].composite_angle << "/" << active_line_->end_points[0].cycles_since_end_of_horizontal_retrace << " -> ";
-				std::cout << active_line_->end_points[1].composite_angle << "/" << active_line_->end_points[1].cycles_since_end_of_horizontal_retrace << " => ";
-				std::cout << (active_line_->end_points[1].composite_angle - active_line_->end_points[0].composite_angle) << "/" << (active_line_->end_points[1].cycles_since_end_of_horizontal_retrace - active_line_->end_points[0].cycles_since_end_of_horizontal_retrace) << " => ";
-				std::cout << double(active_line_->end_points[1].composite_angle - active_line_->end_points[0].composite_angle) / (double(active_line_->end_points[1].cycles_since_end_of_horizontal_retrace - active_line_->end_points[0].cycles_since_end_of_horizontal_retrace) * 64.0f);
-				std::cout << std::endl;
-			}
-#endif
-		}
-
-		// A line is complete; submit latest updates if nothing failed.
-		if(allocation_has_failed_) {
-			// Reset all pointers to where they were; this also means
-			// the stencil won't be properly populated.
-			write_pointers_ = submit_pointers_.load();
-			frame_is_complete_ = false;
-		} else {
-			// Advance submit pointer.
-			submit_pointers_.store(write_pointers_);
-		}
-		allocation_has_failed_ = false;
-	}
-	output_is_visible_ = is_visible;
-}
-
 void ScanTarget::setup_pipeline() {
 	const auto data_type_size = Outputs::Display::size_for_data_type(modals_.input_data_type);
 
@@ -400,10 +170,6 @@ void ScanTarget::setup_pipeline() {
 	input_shader_->set_uniform("textureName", GLint(SourceDataTextureUnit - GL_TEXTURE0));
 }
 
-const Outputs::Display::Metrics &BufferingScanTarget::display_metrics() {
-	return display_metrics_;
-}
-
 bool ScanTarget::is_soft_display_type() {
 	return modals_.display_type == DisplayType::CompositeColour || modals_.display_type == DisplayType::CompositeMonochrome;
 }

Outputs/OpenGL/ScanTarget.hpp

@@ -11,7 +11,7 @@
 
 #include "../Log.hpp"
 #include "../DisplayMetrics.hpp"
-#include "../ScanTarget.hpp"
+#include "../ScanTargets/BufferingScanTarget.hpp"
 
 #include "OpenGL.hpp"
 #include "Primitives/TextureTarget.hpp"
@@ -32,150 +32,13 @@ namespace Outputs {
 namespace Display {
 namespace OpenGL {
 
-/*!
-	Provides basic thread-safe (hopefully) circular queues for any scan target that:
-
-		*	will store incoming Scans into a linear circular buffer and pack regions of
-			incoming pixel data into a 2d texture;
-		*	will compose whole lines of content by partioning the Scans based on sync
-			placement and then pasting together their content;
-		*	will process those lines as necessary to map from input format to whatever
-			suits the display; and
-		*	will then output the lines.
-
-	This buffer rejects new data when full.
-*/
-class BufferingScanTarget: public Outputs::Display::ScanTarget {
-	public:
-		/*! @returns The DisplayMetrics object that this ScanTarget has been providing with announcements and draw overages. */
-		const Metrics &display_metrics();
-
-	protected:
-		// Extends the definition of a Scan to include two extra fields,
-		// completing this scan's source data and destination locations.
-		struct Scan {
-			Outputs::Display::ScanTarget::Scan scan;
-
-			/// Stores the y coordinate for this scan's data within the write area texture.
-			/// Use this plus the scan's endpoints' data_offsets to locate this data in 2d.
-			uint16_t data_y;
-			/// Stores the y coordinate assigned to this scan within the intermediate buffers.
-			/// Use this plus this scan's endpoints' x locations to determine where to composite
-			/// this data for intermediate processing.
-			uint16_t line;
-		};
-
-		/// Defines the boundaries of a complete line of video — a 2d start and end location,
-		/// composite phase and amplitude (if relevant), the source line in the intermediate buffer
-		/// plus the start and end offsets of the area that is visible from the intermediate buffer.
-		struct Line {
-			struct EndPoint {
-				uint16_t x, y;
-				uint16_t cycles_since_end_of_horizontal_retrace;
-				int16_t composite_angle;
-			} end_points[2];
-			uint16_t line;
-			uint8_t composite_amplitude;
-		};
-
-		/// Provides additional metadata about lines; this is separate because it's unlikely to be of
-		/// interest to the GPU, unlike the fields in Line.
-		struct LineMetadata {
-			/// @c true if this line was the first drawn after vertical sync; @c false otherwise.
-			bool is_first_in_frame;
-			/// @c true if this line is the first in the frame and if every single piece of output
-			/// from the previous frame was recorded; @c false otherwise. Data can be dropped
-			/// from a frame if performance problems mean that the emulated machine is running
-			/// more quickly than complete frames can be generated.
-			bool previous_frame_was_complete;
-		};
-
-		// TODO: put this behind accessors.
-		std::atomic_flag is_updating_;
-
-		// These are safe to read if you have is_updating_.
-		Modals modals_;
-		bool modals_are_dirty_ = false;
-
-		// Track allocation failures.
-		bool data_is_allocated_ = false;
-		bool allocation_has_failed_ = false;
-
-		/// Maintains a buffer of the most recent scans.
-		// TODO: have the owner supply a buffer and its size.
-		// That'll allow owners to place this in shared video memory if possible.
-		std::array<Scan, 16384> scan_buffer_;
-
-		/// A mutex for gettng access to write_pointers_; access to write_pointers_,
-		/// data_type_size_ or write_area_texture_ is almost never contended, so this
-		/// is cheap for the main use case.
-		std::mutex write_pointers_mutex_;
-
-		struct PointerSet {
-			// This constructor is here to appease GCC's interpretation of
-			// an ambiguity in the C++ standard; cf. https://stackoverflow.com/questions/17430377
-			PointerSet() noexcept {}
-
-			// Squeezing this struct into 64 bits makes the std::atomics more likely
-			// to be lock free; they are under LLVM x86-64.
-			int write_area = 1;	// By convention this points to the vended area. Which is preceded by a guard pixel. So a sensible default construction is write_area = 1.
-			uint16_t scan_buffer = 0;
-			uint16_t line = 0;
-		};
-
-		/// A pointer to the next thing that should be provided to the caller for data.
-		PointerSet write_pointers_;
-
-		/// A pointer to the final thing currently cleared for submission.
-		std::atomic<PointerSet> submit_pointers_;
-
-		/// A pointer to the first thing not yet submitted for display.
-		std::atomic<PointerSet> read_pointers_;
-
-		// Ephemeral state that helps in line composition.
-		Line *active_line_ = nullptr;
-		int provided_scans_ = 0;
-		bool is_first_in_frame_ = true;
-		bool frame_is_complete_ = true;
-		bool previous_frame_was_complete_ = true;
-
-		// Ephemeral information for the begin/end functions.
-		Scan *vended_scan_ = nullptr;
-		int vended_write_area_pointer_ = 0;
-
-		static constexpr int WriteAreaWidth = 2048;
-		static constexpr int WriteAreaHeight = 2048;
-
-		static constexpr int LineBufferWidth = 2048;
-		static constexpr int LineBufferHeight = 2048;
-
-		Metrics display_metrics_;
-
-		// Uses a texture to vend write areas.
-		std::vector<uint8_t> write_area_texture_;
-		size_t data_type_size_ = 0;
-
-		bool output_is_visible_ = false;
-
-		std::array<Line, LineBufferHeight> line_buffer_;
-		std::array<LineMetadata, LineBufferHeight> line_metadata_buffer_;
-
-	private:
-		// ScanTarget overrides.
-		void set_modals(Modals) final;
-		Outputs::Display::ScanTarget::Scan *begin_scan() final;
-		void end_scan() final;
-		uint8_t *begin_data(size_t required_length, size_t required_alignment) final;
-		void end_data(size_t actual_length) final;
-		void announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t colour_burst_amplitude) final;
-};
 
 /*!
 	Provides a ScanTarget that uses OpenGL to render its output;
 	this uses various internal buffers so that the only geometry
 	drawn to the target framebuffer is a quad.
 */
-class ScanTarget: public BufferingScanTarget {
+class ScanTarget: public Outputs::Display::BufferingScanTarget {
 	public:
 		ScanTarget(GLuint target_framebuffer = 0, float output_gamma = 2.2f);
 		~ScanTarget();
@@ -200,9 +63,6 @@ class ScanTarget: public BufferingScanTarget {
 		GLuint target_framebuffer_;
 		const float output_gamma_;
 
-		// Outputs::Display::ScanTarget finals.
-		void will_change_owner() final;
-
 		int resolution_reduction_level_ = 1;
 		int output_height_ = 0;
 

Outputs/ScanTargets/BufferingScanTarget.cpp

@@ -0,0 +1,240 @@
+//
+//  BufferingScanTarget.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 22/07/2020.
+//  Copyright © 2020 Thomas Harte. All rights reserved.
+//
+
+#include "BufferingScanTarget.hpp"
+
+using namespace Outputs::Display;
+
+void BufferingScanTarget::set_modals(Modals modals) {
+	// Don't change the modals while drawing is ongoing; a previous set might be
+	// in the process of being established.
+	while(is_updating_.test_and_set());
+	modals_ = modals;
+	modals_are_dirty_ = true;
+	is_updating_.clear();
+}
+
+void BufferingScanTarget::end_scan() {
+	if(vended_scan_) {
+		std::lock_guard lock_guard(write_pointers_mutex_);
+		vended_scan_->data_y = TextureAddressGetY(vended_write_area_pointer_);
+		vended_scan_->line = write_pointers_.line;
+		vended_scan_->scan.end_points[0].data_offset += TextureAddressGetX(vended_write_area_pointer_);
+		vended_scan_->scan.end_points[1].data_offset += TextureAddressGetX(vended_write_area_pointer_);
+
+#ifdef LOG_SCANS
+		if(vended_scan_->scan.composite_amplitude) {
+			std::cout << "S: ";
+			std::cout << vended_scan_->scan.end_points[0].composite_angle << "/" << vended_scan_->scan.end_points[0].data_offset << "/" << vended_scan_->scan.end_points[0].cycles_since_end_of_horizontal_retrace << " -> ";
+			std::cout << vended_scan_->scan.end_points[1].composite_angle << "/" << vended_scan_->scan.end_points[1].data_offset << "/" << vended_scan_->scan.end_points[1].cycles_since_end_of_horizontal_retrace << " => ";
+			std::cout << double(vended_scan_->scan.end_points[1].composite_angle - vended_scan_->scan.end_points[0].composite_angle) / (double(vended_scan_->scan.end_points[1].data_offset - vended_scan_->scan.end_points[0].data_offset) * 64.0f) << "/";
+			std::cout << double(vended_scan_->scan.end_points[1].composite_angle - vended_scan_->scan.end_points[0].composite_angle) / (double(vended_scan_->scan.end_points[1].cycles_since_end_of_horizontal_retrace - vended_scan_->scan.end_points[0].cycles_since_end_of_horizontal_retrace) * 64.0f);
+			std::cout << std::endl;
+		}
+#endif
+	}
+	vended_scan_ = nullptr;
+}
+
+uint8_t *BufferingScanTarget::begin_data(size_t required_length, size_t required_alignment) {
+	assert(required_alignment);
+
+	if(allocation_has_failed_) return nullptr;
+
+	std::lock_guard lock_guard(write_pointers_mutex_);
+	if(write_area_texture_.empty()) {
+		allocation_has_failed_ = true;
+		return nullptr;
+	}
+
+	// Determine where the proposed write area would start and end.
+	uint16_t output_y = TextureAddressGetY(write_pointers_.write_area);
+
+	uint16_t aligned_start_x = TextureAddressGetX(write_pointers_.write_area & 0xffff) + 1;
+	aligned_start_x += uint16_t((required_alignment - aligned_start_x%required_alignment)%required_alignment);
+
+	uint16_t end_x = aligned_start_x + uint16_t(1 + required_length);
+
+	if(end_x > WriteAreaWidth) {
+		output_y = (output_y + 1) % WriteAreaHeight;
+		aligned_start_x = uint16_t(required_alignment);
+		end_x = aligned_start_x + uint16_t(1 + required_length);
+	}
+
+	// Check whether that steps over the read pointer.
+	const auto end_address = TextureAddress(end_x, output_y);
+	const auto read_pointers = read_pointers_.load();
+
+	const auto end_distance = TextureSub(end_address, read_pointers.write_area);
+	const auto previous_distance = TextureSub(write_pointers_.write_area, read_pointers.write_area);
+
+	// If allocating this would somehow make the write pointer back away from the read pointer,
+	// there must not be enough space left.
+	if(end_distance < previous_distance) {
+		allocation_has_failed_ = true;
+		return nullptr;
+	}
+
+	// Everything checks out, note expectation of a future end_data and return the pointer.
+	data_is_allocated_ = true;
+	vended_write_area_pointer_ = write_pointers_.write_area = TextureAddress(aligned_start_x, output_y);
+
+	assert(write_pointers_.write_area >= 1 && ((size_t(write_pointers_.write_area) + required_length + 1) * data_type_size_) <= write_area_texture_.size());
+	return &write_area_texture_[size_t(write_pointers_.write_area) * data_type_size_];
+
+	// Note state at exit:
+	//		write_pointers_.write_area points to the first pixel the client is expected to draw to.
+}
+
+void BufferingScanTarget::end_data(size_t actual_length) {
+	if(allocation_has_failed_ || !data_is_allocated_) return;
+
+	std::lock_guard lock_guard(write_pointers_mutex_);
+
+	// Bookend the start of the new data, to safeguard for precision errors in sampling.
+	memcpy(
+		&write_area_texture_[size_t(write_pointers_.write_area - 1) * data_type_size_],
+		&write_area_texture_[size_t(write_pointers_.write_area) * data_type_size_],
+		data_type_size_);
+
+	// Advance to the end of the current run.
+	write_pointers_.write_area += actual_length + 1;
+
+	// Also bookend the end.
+	memcpy(
+		&write_area_texture_[size_t(write_pointers_.write_area - 1) * data_type_size_],
+		&write_area_texture_[size_t(write_pointers_.write_area - 2) * data_type_size_],
+		data_type_size_);
+
+	// The write area was allocated in the knowledge that there's sufficient
+	// distance left on the current line, but there's a risk of exactly filling
+	// the final line, in which case this should wrap back to 0.
+	write_pointers_.write_area %= (write_area_texture_.size() / data_type_size_);
+
+	// Record that no further end_data calls are expected.
+	data_is_allocated_ = false;
+}
+
+void BufferingScanTarget::will_change_owner() {
+	allocation_has_failed_ = true;
+	vended_scan_ = nullptr;
+}
+
+void BufferingScanTarget::announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t composite_amplitude) {
+	// Forward the event to the display metrics tracker.
+	display_metrics_.announce_event(event);
+
+	if(event == ScanTarget::Event::EndVerticalRetrace) {
+		// The previous-frame-is-complete flag is subject to a two-slot queue because
+		// measurement for *this* frame needs to begin now, meaning that the previous
+		// result needs to be put somewhere — it'll be attached to the first successful
+		// line output.
+		is_first_in_frame_ = true;
+		previous_frame_was_complete_ = frame_is_complete_;
+		frame_is_complete_ = true;
+	}
+
+	if(output_is_visible_ == is_visible) return;
+	if(is_visible) {
+		const auto read_pointers = read_pointers_.load();
+		std::lock_guard lock_guard(write_pointers_mutex_);
+
+		// Commit the most recent line only if any scans fell on it.
+		// Otherwise there's no point outputting it, it'll contribute nothing.
+		if(provided_scans_) {
+			// Store metadata if concluding a previous line.
+			if(active_line_) {
+				line_metadata_buffer_[size_t(write_pointers_.line)].is_first_in_frame = is_first_in_frame_;
+				line_metadata_buffer_[size_t(write_pointers_.line)].previous_frame_was_complete = previous_frame_was_complete_;
+				is_first_in_frame_ = false;
+			}
+
+			// Attempt to allocate a new line; note allocation failure if necessary.
+			const auto next_line = uint16_t((write_pointers_.line + 1) % LineBufferHeight);
+			if(next_line == read_pointers.line) {
+				allocation_has_failed_ = true;
+				active_line_ = nullptr;
+			} else {
+				write_pointers_.line = next_line;
+				active_line_ = &line_buffer_[size_t(write_pointers_.line)];
+			}
+			provided_scans_ = 0;
+		}
+
+		if(active_line_) {
+			active_line_->end_points[0].x = location.x;
+			active_line_->end_points[0].y = location.y;
+			active_line_->end_points[0].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
+			active_line_->end_points[0].composite_angle = location.composite_angle;
+			active_line_->line = write_pointers_.line;
+			active_line_->composite_amplitude = composite_amplitude;
+		}
+	} else {
+		if(active_line_) {
+			// A successfully-allocated line is ending.
+			active_line_->end_points[1].x = location.x;
+			active_line_->end_points[1].y = location.y;
+			active_line_->end_points[1].cycles_since_end_of_horizontal_retrace = location.cycles_since_end_of_horizontal_retrace;
+			active_line_->end_points[1].composite_angle = location.composite_angle;
+
+#ifdef LOG_LINES
+			if(active_line_->composite_amplitude) {
+				std::cout << "L: ";
+				std::cout << active_line_->end_points[0].composite_angle << "/" << active_line_->end_points[0].cycles_since_end_of_horizontal_retrace << " -> ";
+				std::cout << active_line_->end_points[1].composite_angle << "/" << active_line_->end_points[1].cycles_since_end_of_horizontal_retrace << " => ";
+				std::cout << (active_line_->end_points[1].composite_angle - active_line_->end_points[0].composite_angle) << "/" << (active_line_->end_points[1].cycles_since_end_of_horizontal_retrace - active_line_->end_points[0].cycles_since_end_of_horizontal_retrace) << " => ";
+				std::cout << double(active_line_->end_points[1].composite_angle - active_line_->end_points[0].composite_angle) / (double(active_line_->end_points[1].cycles_since_end_of_horizontal_retrace - active_line_->end_points[0].cycles_since_end_of_horizontal_retrace) * 64.0f);
+				std::cout << std::endl;
+			}
+#endif
+		}
+
+		// A line is complete; submit latest updates if nothing failed.
+		if(allocation_has_failed_) {
+			// Reset all pointers to where they were; this also means
+			// the stencil won't be properly populated.
+			write_pointers_ = submit_pointers_.load();
+			frame_is_complete_ = false;
+		} else {
+			// Advance submit pointer.
+			submit_pointers_.store(write_pointers_);
+		}
+		allocation_has_failed_ = false;
+	}
+	output_is_visible_ = is_visible;
+}
+
+const Outputs::Display::Metrics &BufferingScanTarget::display_metrics() {
+	return display_metrics_;
+}
+
+Outputs::Display::ScanTarget::Scan *BufferingScanTarget::begin_scan() {
+	if(allocation_has_failed_) return nullptr;
+
+	std::lock_guard lock_guard(write_pointers_mutex_);
+
+	const auto result = &scan_buffer_[write_pointers_.scan_buffer];
+	const auto read_pointers = read_pointers_.load();
+
+	// Advance the pointer.
+	const auto next_write_pointer = decltype(write_pointers_.scan_buffer)((write_pointers_.scan_buffer + 1) % scan_buffer_.size());
+
+	// Check whether that's too many.
+	if(next_write_pointer == read_pointers.scan_buffer) {
+		allocation_has_failed_ = true;
+		return nullptr;
+	}
+	write_pointers_.scan_buffer = next_write_pointer;
+	++provided_scans_;
+
+	// Fill in extra OpenGL-specific details.
+	result->line = write_pointers_.line;
+
+	vended_scan_ = result;
+	return &result->scan;
+}

Outputs/ScanTargets/BufferingScanTarget.hpp

@@ -0,0 +1,171 @@
+//
+//  BufferingScanTarget.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 22/07/2020.
+//  Copyright © 2020 Thomas Harte. All rights reserved.
+//
+
+#ifndef BufferingScanTarget_hpp
+#define BufferingScanTarget_hpp
+
+#include "../ScanTarget.hpp"
+#include "../DisplayMetrics.hpp"
+
+#include <array>
+#include <atomic>
+#include <mutex>
+#include <vector>
+
+#define TextureAddress(x, y)	(((y) << 11) | (x))
+#define TextureAddressGetY(v)	uint16_t((v) >> 11)
+#define TextureAddressGetX(v)	uint16_t((v) & 0x7ff)
+#define TextureSub(a, b)		(((a) - (b)) & 0x3fffff)
+
+namespace Outputs {
+namespace Display {
+
+/*!
+	Provides basic thread-safe (hopefully) circular queues for any scan target that:
+
+		*	will store incoming Scans into a linear circular buffer and pack regions of
+			incoming pixel data into a 2d texture;
+		*	will compose whole lines of content by partioning the Scans based on sync
+			placement and then pasting together their content;
+		*	will process those lines as necessary to map from input format to whatever
+			suits the display; and
+		*	will then output the lines.
+
+	This buffer rejects new data when full.
+*/
+class BufferingScanTarget: public Outputs::Display::ScanTarget {
+	public:
+		/*! @returns The DisplayMetrics object that this ScanTarget has been providing with announcements and draw overages. */
+		const Metrics &display_metrics();
+
+	protected:
+		// Extends the definition of a Scan to include two extra fields,
+		// completing this scan's source data and destination locations.
+		struct Scan {
+			Outputs::Display::ScanTarget::Scan scan;
+
+			/// Stores the y coordinate for this scan's data within the write area texture.
+			/// Use this plus the scan's endpoints' data_offsets to locate this data in 2d.
+			uint16_t data_y;
+			/// Stores the y coordinate assigned to this scan within the intermediate buffers.
+			/// Use this plus this scan's endpoints' x locations to determine where to composite
+			/// this data for intermediate processing.
+			uint16_t line;
+		};
+
+		/// Defines the boundaries of a complete line of video — a 2d start and end location,
+		/// composite phase and amplitude (if relevant), the source line in the intermediate buffer
+		/// plus the start and end offsets of the area that is visible from the intermediate buffer.
+		struct Line {
+			struct EndPoint {
+				uint16_t x, y;
+				uint16_t cycles_since_end_of_horizontal_retrace;
+				int16_t composite_angle;
+			} end_points[2];
+			uint16_t line;
+			uint8_t composite_amplitude;
+		};
+
+		/// Provides additional metadata about lines; this is separate because it's unlikely to be of
+		/// interest to the GPU, unlike the fields in Line.
+		struct LineMetadata {
+			/// @c true if this line was the first drawn after vertical sync; @c false otherwise.
+			bool is_first_in_frame;
+			/// @c true if this line is the first in the frame and if every single piece of output
+			/// from the previous frame was recorded; @c false otherwise. Data can be dropped
+			/// from a frame if performance problems mean that the emulated machine is running
+			/// more quickly than complete frames can be generated.
+			bool previous_frame_was_complete;
+		};
+
+		// TODO: put this behind accessors.
+		std::atomic_flag is_updating_;
+
+		// These are safe to read if you have is_updating_.
+		Modals modals_;
+		bool modals_are_dirty_ = false;
+
+		// Track allocation failures.
+		bool data_is_allocated_ = false;
+		bool allocation_has_failed_ = false;
+
+		/// Maintains a buffer of the most recent scans.
+		// TODO: have the owner supply a buffer and its size.
+		// That'll allow owners to place this in shared video memory if possible.
+		std::array<Scan, 16384> scan_buffer_;
+
+		/// A mutex for gettng access to write_pointers_; access to write_pointers_,
+		/// data_type_size_ or write_area_texture_ is almost never contended, so this
+		/// is cheap for the main use case.
+		std::mutex write_pointers_mutex_;
+
+		struct PointerSet {
+			// This constructor is here to appease GCC's interpretation of
+			// an ambiguity in the C++ standard; cf. https://stackoverflow.com/questions/17430377
+			PointerSet() noexcept {}
+
+			// Squeezing this struct into 64 bits makes the std::atomics more likely
+			// to be lock free; they are under LLVM x86-64.
+			int write_area = 1;	// By convention this points to the vended area. Which is preceded by a guard pixel. So a sensible default construction is write_area = 1.
+			uint16_t scan_buffer = 0;
+			uint16_t line = 0;
+		};
+
+		/// A pointer to the next thing that should be provided to the caller for data.
+		PointerSet write_pointers_;
+
+		/// A pointer to the final thing currently cleared for submission.
+		std::atomic<PointerSet> submit_pointers_;
+
+		/// A pointer to the first thing not yet submitted for display.
+		std::atomic<PointerSet> read_pointers_;
+
+		// Ephemeral state that helps in line composition.
+		Line *active_line_ = nullptr;
+		int provided_scans_ = 0;
+		bool is_first_in_frame_ = true;
+		bool frame_is_complete_ = true;
+		bool previous_frame_was_complete_ = true;
+
+		// Ephemeral information for the begin/end functions.
+		Scan *vended_scan_ = nullptr;
+		int vended_write_area_pointer_ = 0;
+
+		static constexpr int WriteAreaWidth = 2048;
+		static constexpr int WriteAreaHeight = 2048;
+
+		static constexpr int LineBufferWidth = 2048;
+		static constexpr int LineBufferHeight = 2048;
+
+		Metrics display_metrics_;
+
+		// Uses a texture to vend write areas.
+		std::vector<uint8_t> write_area_texture_;
+		size_t data_type_size_ = 0;
+
+		bool output_is_visible_ = false;
+
+		std::array<Line, LineBufferHeight> line_buffer_;
+		std::array<LineMetadata, LineBufferHeight> line_metadata_buffer_;
+
+	private:
+		// ScanTarget overrides.
+		void set_modals(Modals) final;
+		Outputs::Display::ScanTarget::Scan *begin_scan() final;
+		void end_scan() final;
+		uint8_t *begin_data(size_t required_length, size_t required_alignment) final;
+		void end_data(size_t actual_length) final;
+		void announce(Event event, bool is_visible, const Outputs::Display::ScanTarget::Scan::EndPoint &location, uint8_t colour_burst_amplitude) final;
+		void will_change_owner() final;
+};
+
+
+}
+}
+
+#endif /* BufferingScanTarget_hpp */