simple_opengl2d.cpp

#include <SFML/OpenGL.hpp>
#include <SFML/Window.hpp>
#include <vector>

int main()
{
	sf::Window window(sf::VideoMode(800, 600), "OpenGL");

	// Set the viewport
	glViewport(0, 0, window.getSize().x, window.getSize().y);

	// Initialize Projection Matrix
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	// Set drawing surface properties - either Perspective or Orthographic: make origin (0,0) at top-left corner of screen
	glOrtho(0.0, window.getSize().x, window.getSize().y, 0.0, -1.0, 1.0);

	// Initialize Modelview Matrix
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	// Initialize Texture Matrix
	glMatrixMode(GL_TEXTURE);
	glPushMatrix();

	// Initialize vertices: use window coordinate for width and height
	auto width = static_cast<float>(window.getSize().x);
	auto height = static_cast<float>(window.getSize().y);

	std::vector<float> vertices =
	{
		0,     0,
		0,     height,
		width, height,
		width, 0
	};

	// Initialize colors
	std::vector<float> colors =
	{
		1, 0, 0,
		0, 1, 0,
		0, 0, 1,
		0, 1, 1
	};

	// Initialize texture virtice
	std::vector<float> texCoord =
	{
		0, 0,
		0, 1,
		1, 1,
		1, 0
	};
	
	// Create texture: simple chess board 8x8
	auto numRows = 8u;
	auto numCols = 8u;
	auto character = 172u;
	auto remain = 255u - character;
	std::vector<unsigned char> texture(numCols * numRows);
	for (auto i = 0u; i < texture.size(); ++i)
		texture[i] = ((i + (i / numCols)) % 2) * remain + character;

	// Upload to GPU texture
	unsigned textureID;
	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_2D, textureID);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, numCols, numRows, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, texture.data());

	// Initialize clear colors
	glClearColor(0.f, 0.f, 0.f, 1.f);

	// Activate necessary states
	glEnable(GL_TEXTURE_2D);

	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);

	glVertexPointer(2, GL_FLOAT, 0, vertices.data());
	glColorPointer(3, GL_FLOAT, 0, colors.data());
	glTexCoordPointer(2, GL_FLOAT, 0, texCoord.data());

	while (window.isOpen())
	{
		sf::Event windowEvent;
		while (window.pollEvent(windowEvent))
		{
			if (windowEvent.type == sf::Event::Closed)
				window.close();
		}

		// render
		glClear(GL_COLOR_BUFFER_BIT);

		glDrawArrays(GL_QUADS, 0, 4);

		window.display();
	}
}

simple_opengl2d_as_SFML.cpp

#include <SFML/OpenGL.hpp>
#include <SFML/Window.hpp>
#include <vector>

int main()
{
	sf::Window window(sf::VideoMode(800, 600), "OpenGL");

	// Set Orthographic
	auto width = static_cast<float>(window.getSize().x);
	auto height = static_cast<float>(window.getSize().y);
	auto a = 2.f / width;
	auto b = 2.f / height;
	std::vector<float> matrix =
	{
		 a , 0, 0, 0,
		 0, -b, 0, 0,
		 0,  0, 1, 0,
		-1,  1, 0, 1
	};

	// Set the projection matrix
	glMatrixMode(GL_PROJECTION);
	glLoadMatrixf(matrix.data());

	// Initialize vertices: 
	std::vector<float> vertices =
	{
		0,     0,
		0,     height,
		width, height,
		width, 0
	};

	// Initialize colors
	std::vector<float> colors =
	{
		1, 0, 0,
		0, 1, 0,
		0, 0, 1,
		0, 1, 1
	};

	// Initialize texture virtice
	std::vector<float> texCoord =
	{
		0, 0,
		0, 1,
		1, 1,
		1, 0
	};

	// Create texture: simple chess board 8x8
	auto numRows = 8u;
	auto numCols = 8u;
	auto character = 172u;
	auto remain = 255u - character;
	std::vector<unsigned char> texture(numCols * numRows);
	for (auto i = 0u; i < texture.size(); ++i)
		texture[i] = ((i + (i / numCols)) % 2) * remain + character;

	// Upload to GPU texture
	unsigned textureID;
	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_2D, textureID);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, numCols, numRows, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, texture.data());

	// Initialize clear colors
	glClearColor(0.f, 0.f, 0.f, 1.f);

	// Activate necessary states
	glEnable(GL_TEXTURE_2D);

	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);

	glVertexPointer(2, GL_FLOAT, 0, vertices.data());
	glColorPointer(3, GL_FLOAT, 0, colors.data());
	glTexCoordPointer(2, GL_FLOAT, 0, texCoord.data());

	while (window.isOpen())
	{
		sf::Event windowEvent;
		while (window.pollEvent(windowEvent))
		{
			if (windowEvent.type == sf::Event::Closed)
				window.close();
		}

		// render
		glClear(GL_COLOR_BUFFER_BIT);

		glDrawArrays(GL_QUADS, 0, 4);

		window.display();
	}
}

simple_opengl2d_NDC.cpp

#include <SFML/OpenGL.hpp>
#include <SFML/Window.hpp>
#include <vector>

int main()
{
	sf::Window window(sf::VideoMode(800, 600), "OpenGL");

	// Initialize vertices: 
	std::vector<GLfloat> vertices =
	{ 
		-1,  1, 
		-1, -1,
		 1, -1,
		 1,  1,
	};

	// Initialize colors
	std::vector<GLfloat> colors =
	{
		1, 0, 0,
		0, 1, 0,
		0, 0, 1,
		0, 1, 1
	};

	// Initialize texture virtice
	std::vector<GLfloat> texCoord =
	{
		0, 0,
		0, 1,
		1, 1,
		1, 0
	};
	
	// Create texture: simple chess board 8x8
	auto numRows = 8u;
	auto numCols = 8u;
	auto character = 172u;
	auto remain = 255u - character;
	std::vector<unsigned char> texture(numCols * numRows);
	for (auto i = 0u; i < texture.size(); ++i)
		texture[i] = ((i + (i / numCols)) % 2) * remain + character;

	// Upload to GPU texture
	GLuint textureID;
	glGenTextures(1, &textureID);
	glBindTexture(GL_TEXTURE_2D, textureID);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, numCols, numRows, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, texture.data());

	// Initialize clear colors
	glClearColor(0.f, 0.f, 0.f, 1.f);

	// Activate necessary states
	glEnable(GL_TEXTURE_2D);

	glEnableClientState(GL_VERTEX_ARRAY);
	glEnableClientState(GL_COLOR_ARRAY);
	glEnableClientState(GL_TEXTURE_COORD_ARRAY);

	glVertexPointer(2, GL_FLOAT, 0, vertices.data());
	glColorPointer(3, GL_FLOAT, 0, colors.data());
	glTexCoordPointer(2, GL_FLOAT, 0, texCoord.data());

	while (window.isOpen())
	{
		sf::Event windowEvent;
		while (window.pollEvent(windowEvent))
		{
			if (windowEvent.type == sf::Event::Closed)
				window.close();
		}

		// render
		glClear(GL_COLOR_BUFFER_BIT);

		glDrawArrays(GL_QUADS, 0, 4);

		window.display();
	}
}