CLK/Outputs/OpenGL/Primitives/Rectangle.cpp

//
//  Rectangle.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 11/07/2018.
//  Copyright © 2018 Thomas Harte. All rights reserved.
//

#include "Rectangle.hpp"

using namespace Outputs::Display::OpenGL;

Rectangle::Rectangle(float x, float y, float width, float height):
	pixel_shader_(
		"#version 150\n"

		"in vec2 position;"

		"void main(void)"
		"{"
			"gl_Position = vec4(position, 0.0, 1.0);"
		"}",

		"#version 150\n"

		"uniform vec4 colour;"
		"out vec4 fragColour;"

		"void main(void)"
		"{"
			"fragColour = colour;"
		"}"
	){
	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 position_attribute = pixel_shader_.get_attrib_location("position");
	glEnableVertexAttribArray(static_cast<GLuint>(position_attribute));

	glVertexAttribPointer(
		(GLuint)position_attribute,
		2,
		GL_FLOAT,
		GL_FALSE,
		2 * sizeof(GLfloat),
		(void *)0);

	colour_uniform_ = pixel_shader_.get_uniform_location("colour");

	float buffer[4*2];

	// Store positions.
	buffer[0] = x;			buffer[1] = y;
	buffer[2] = x;			buffer[3] = y + height;
	buffer[4] = x + width;	buffer[5] = y;
	buffer[6] = x + width;	buffer[7] = y + height;

	// Upload buffer.
	glBindBuffer(GL_ARRAY_BUFFER, drawing_array_buffer_);
	glBufferData(GL_ARRAY_BUFFER, sizeof(buffer), buffer, GL_STATIC_DRAW);
}

void Rectangle::draw(float red, float green, float blue) {
	pixel_shader_.bind();
	glUniform4f(colour_uniform_, red, green, blue, 1.0);

	glBindVertexArray(drawing_vertex_array_);
	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}