CLK/Outputs/CRT/Internals/TextureTarget.cpp

//
//  TextureTarget.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 07/02/2016.
//  Copyright © 2016 Thomas Harte. All rights reserved.
//

#include "TextureTarget.hpp"

#include <cmath>
#include <cstdlib>

using namespace OpenGL;

TextureTarget::TextureTarget(GLsizei width, GLsizei height, GLenum texture_unit, GLint mag_filter) :
		_width(width),
		_height(height),
		_texture_unit(texture_unit),
		_set_aspect_ratio(0.0f) {
	glGenFramebuffers(1, &_framebuffer);
	glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);

	_expanded_width = 1 << (GLsizei)ceil(log2(width));
	_expanded_height = 1 << (GLsizei)ceil(log2(height));

	glGenTextures(1, &_texture);
	glActiveTexture(texture_unit);
	glBindTexture(GL_TEXTURE_2D, _texture);
	uint8_t *blank_buffer = static_cast<uint8_t *>(calloc(static_cast<std::size_t>(_expanded_width * _expanded_height), 4));
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)_expanded_width, (GLsizei)_expanded_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, blank_buffer);
	free(blank_buffer);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, mag_filter);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture, 0);

	if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		throw ErrorFramebufferIncomplete;
}

TextureTarget::~TextureTarget() {
	glDeleteFramebuffers(1, &_framebuffer);
	glDeleteTextures(1, &_texture);
	if(_drawing_vertex_array) glDeleteVertexArrays(1, &_drawing_vertex_array);
	if(_drawing_array_buffer) glDeleteBuffers(1, &_drawing_array_buffer);
}

void TextureTarget::bind_framebuffer() {
	glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
	glViewport(0, 0, _width, _height);
}

void TextureTarget::bind_texture() {
	glBindTexture(GL_TEXTURE_2D, _texture);
}

void TextureTarget::draw(float aspect_ratio) {
	if(!_pixel_shader) {
		const char *vertex_shader =
			"#version 150\n"

			"in vec2 texCoord;"
			"in vec2 position;"

			"out vec2 texCoordVarying;"

			"void main(void)"
			"{"
				"texCoordVarying = texCoord;"
				"gl_Position = vec4(position, 0.0, 1.0);"
			"}";
		const char *fragment_shader =
			"#version 150\n"

			"in vec2 texCoordVarying;"
			"uniform sampler2D texID;"
			"out vec4 fragColour;"

			"void main(void)"
			"{"
				"fragColour = texture(texID, texCoordVarying);"
			"}";
		_pixel_shader.reset(new Shader(vertex_shader, fragment_shader, nullptr));
		_pixel_shader->bind();

		glGenVertexArrays(1, &_drawing_vertex_array);
		glGenBuffers(1, &_drawing_array_buffer);

		glBindVertexArray(_drawing_vertex_array);
		glBindBuffer(GL_ARRAY_BUFFER, _drawing_array_buffer);

		GLint positionAttribute			= _pixel_shader->get_attrib_location("position");
		GLint texCoordAttribute			= _pixel_shader->get_attrib_location("texCoord");

		glEnableVertexAttribArray((GLuint)positionAttribute);
		glEnableVertexAttribArray((GLuint)texCoordAttribute);

		const GLsizei vertexStride = 4 * sizeof(GLfloat);
		glVertexAttribPointer((GLuint)positionAttribute,	2, GL_FLOAT,	GL_FALSE,	vertexStride, (void *)0);
		glVertexAttribPointer((GLuint)texCoordAttribute,	2, GL_FLOAT,	GL_FALSE,	vertexStride, (void *)(2 * sizeof(GLfloat)));

		GLint texIDUniform = _pixel_shader->get_uniform_location("texID");
		glUniform1i(texIDUniform, (GLint)(_texture_unit - GL_TEXTURE0));
	}

	if(_set_aspect_ratio != aspect_ratio) {
		_set_aspect_ratio = aspect_ratio;
		float buffer[4*4];

		// establish texture coordinates
		buffer[2] = 0.0f;
		buffer[3] = 0.0f;
		buffer[6] = 0.0f;
		buffer[7] = static_cast<float>(_height) / static_cast<float>(_expanded_height);
		buffer[10] = static_cast<float>(_width) / static_cast<float>(_expanded_width);
		buffer[11] = 0;
		buffer[14] = buffer[10];
		buffer[15] = buffer[7];

		// determine positions; rule is to keep the same height and centre
		float internal_aspect_ratio = static_cast<float>(_width) / static_cast<float>(_height);
		float aspect_ratio_ratio = internal_aspect_ratio / aspect_ratio;

		buffer[0] = -aspect_ratio_ratio;	buffer[1] = -1.0f;
		buffer[4] = -aspect_ratio_ratio;	buffer[5] = 1.0f;
		buffer[8] = aspect_ratio_ratio;		buffer[9] = -1.0f;
		buffer[12] = aspect_ratio_ratio;	buffer[13] = 1.0f;

		// upload buffer
		glBindBuffer(GL_ARRAY_BUFFER, _drawing_array_buffer);
		glBufferData(GL_ARRAY_BUFFER, sizeof(buffer), buffer, GL_STATIC_DRAW);
	}

	_pixel_shader->bind();
	glBindVertexArray(_drawing_vertex_array);
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}