CLK/Outputs/OpenGL/ScanTarget.hpp

//
//  ScanTarget.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 05/11/2018.
//  Copyright © 2018 Thomas Harte. All rights reserved.
//

#pragma once

#include "Outputs/Log.hpp"
#include "Outputs/DisplayMetrics.hpp"
#include "Outputs/ScanTargets/BufferingScanTarget.hpp"

#include "OpenGL.hpp"
#include "Primitives/TextureTarget.hpp"
#include "Primitives/Rectangle.hpp"

#include "SignalProcessing/FIRFilter.hpp"

#include <array>
#include <atomic>
#include <cstdint>
#include <chrono>
#include <list>
#include <memory>
#include <string>
#include <vector>

namespace Outputs::Display::OpenGL {


/*!
	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 Outputs::Display::BufferingScanTarget {	// TODO: use private inheritance and expose only display_metrics() and a custom cast?
public:
	ScanTarget(GLuint target_framebuffer = 0, float output_gamma = 2.2f);
	~ScanTarget();

	void set_target_framebuffer(GLuint);

	/*! Pushes the current state of output to the target framebuffer. */
	void draw(int output_width, int output_height);
	/*! Processes all the latest input, at a resolution suitable for later output to a framebuffer of the specified size. */
	void update(int output_width, int output_height);

private:
	static constexpr int LineBufferWidth = 2048;
	static constexpr int LineBufferHeight = 2048;

#ifndef NDEBUG
	struct OpenGLVersionDumper {
		OpenGLVersionDumper() {
			// Note the OpenGL version, as the first thing this class does prior to construction.
			Log::Logger<Log::Source::OpenGL>::info().append(
				"Constructing scan target with OpenGL %s; shading language version %s",
				glGetString(GL_VERSION),
				glGetString(GL_SHADING_LANGUAGE_VERSION));
		}
	} dumper_;
#endif

	GLuint target_framebuffer_;
	const float output_gamma_;

	int resolution_reduction_level_ = 1;
	int output_height_ = 0;

	size_t lines_submitted_ = 0;
	std::chrono::high_resolution_clock::time_point line_submission_begin_time_;

	// Contains the first composition of scans into lines;
	// they're accumulated prior to output to allow for continuous
	// application of any necessary conversions — e.g. composite processing.
	TextureTarget unprocessed_line_texture_;

	// Contains pre-lowpass-filtered chrominance information that is
	// part-QAM-demoduled, if dealing with a QAM data source.
	std::unique_ptr<TextureTarget> qam_chroma_texture_;

	// Scans are accumulated to the accumulation texture; the full-display
	// rectangle is used to ensure untouched pixels properly decay.
	std::unique_ptr<TextureTarget> accumulation_texture_;
	Rectangle full_display_rectangle_;
	bool stencil_is_valid_ = false;

	// OpenGL storage handles for buffer data.
	GLuint scan_buffer_name_ = 0, scan_vertex_array_ = 0;
	GLuint line_buffer_name_ = 0, line_vertex_array_ = 0;

	template <typename T> void allocate_buffer(const T &array, GLuint &buffer_name, GLuint &vertex_array_name);
	template <typename T> void patch_buffer(const T &array, GLuint target, uint16_t submit_pointer, uint16_t read_pointer);

	GLuint write_area_texture_name_ = 0;
	bool texture_exists_ = false;

	// Receives scan target modals.
	std::optional<ScanTarget::Modals> existing_modals_;
	void setup_pipeline();

	enum class ShaderType {
		Composition,
		Conversion,
		QAMSeparation
	};

	/*!
		Calls @c taret.enable_vertex_attribute_with_pointer to attach all
		globals for shaders of @c type to @c target.
	*/
	static void enable_vertex_attributes(ShaderType type, Shader &target);
	void set_uniforms(ShaderType type, Shader &target) const;
	std::vector<std::string> bindings(ShaderType type) const;

	GLsync fence_ = nullptr;
	std::atomic_flag is_drawing_to_accumulation_buffer_;

	std::unique_ptr<Shader> input_shader_;
	std::unique_ptr<Shader> output_shader_;
	std::unique_ptr<Shader> qam_separation_shader_;

	/*!
		Produces a shader that composes fragment of the input stream to a single buffer,
		normalising the data into one of four forms: RGB, 8-bit luminance,
		phase-linked luminance or luminance+phase offset.
	*/
	std::unique_ptr<Shader> composition_shader() const;
	/*!
		Produces a shader that reads from a composition buffer and converts to host
		output RGB, decoding composite or S-Video as necessary.
	*/
	std::unique_ptr<Shader> conversion_shader() const;
	/*!
		Produces a shader that writes separated but not-yet filtered QAM components
		from the unprocessed line texture to the QAM chroma texture, at a fixed
		size of four samples per colour clock, point sampled.
	*/
	std::unique_ptr<Shader> qam_separation_shader() const;

	void set_sampling_window(int output_Width, int output_height, Shader &target);

	std::string sampling_function() const;

	/*!
		@returns true if the current display type is a 'soft' one, i.e. one in which
		contrast tends to be low, such as a composite colour display.
	*/
	bool is_soft_display_type();

	// Storage for the various buffers.
	std::vector<uint8_t> write_area_texture_;
	std::array<Scan, LineBufferHeight*5> scan_buffer_;
	std::array<Line, LineBufferHeight> line_buffer_;
	std::array<LineMetadata, LineBufferHeight> line_metadata_buffer_;
};

}