// Compile with
// c++ -std=c++11 ./shared_constant_names.cc -Wall $(pkg-config --cflags --libs sdl2 gl) -o shared_constant_names

#define GL_GLEXT_PROTOTYPES 1
#include <GL/gl.h>
#include <SDL.h>
#include <SDL_video.h>
#include <iostream>
#include <cassert>

const GLchar * const vertex_shader_source =
R"foo(#version 330

in vec2 in_position;

void main()
{
	const float zs[4] = float[4](0, 0, 0, 0);
	gl_Position = vec4(in_position, zs[int(in_position.x) % 4], 1.0);
}
)foo";

const GLchar * const fragment_shader_source =
R"foo(#version 330

void main()
{
	const vec4 colours[2] = vec4[2](vec4(1, 0, 0, 0), vec4(0, 1, 0, 0));
	gl_FragColor = colours[int(gl_FragCoord.x) % 2];
}
)foo";

const GLfloat vertex_positions[][2] = 
	{{-0.4f, -0.4f}, {-0.4f, 0.4f}, {0.4f, 0.4f}};

int main()
{
	SDL_Init(SDL_INIT_VIDEO);
	SDL_Window * const window = SDL_CreateWindow(
		"test",
		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 256, 256,
		SDL_WINDOW_OPENGL);
	if (!window)
	{
		std::cerr << "Could not create window: "
		          << SDL_GetError() << '\n';
		return 1;
	}

	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
	                    SDL_GL_CONTEXT_PROFILE_CORE);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS,
	                    SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG);

	SDL_GLContext gl_context = SDL_GL_CreateContext(window);
	
	glClear(GL_COLOR_BUFFER_BIT);
	GLuint vao;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);
	GLuint vbo;
	glGenBuffers(1, &vbo);
	glBindBuffer(GL_ARRAY_BUFFER, vbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_positions), vertex_positions, GL_STATIC_DRAW);
	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(0);
	
	const GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertex_shader, 1, const_cast<const GLchar**>(&vertex_shader_source), 0);
	glCompileShader(vertex_shader);
	{
		GLint is_compiled;
		glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &is_compiled);
		assert(is_compiled == GL_TRUE);
	}

	const GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragment_shader, 1, const_cast<const GLchar**>(&fragment_shader_source), 0);
	glCompileShader(fragment_shader);
	{
		GLint is_compiled;
		glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &is_compiled);
		assert(is_compiled == GL_TRUE);
	}

	GLuint shader_program = glCreateProgram();
	glAttachShader(shader_program, vertex_shader);
	glAttachShader(shader_program, fragment_shader);
	glBindAttribLocation(shader_program, 0, "in_position");
	glLinkProgram(shader_program);
	{
		GLint is_linked;
		glGetProgramiv(shader_program, GL_LINK_STATUS, &is_linked);
		assert(is_linked == GL_TRUE);
	}
	glUseProgram(shader_program);

	glDrawArrays(GL_TRIANGLES, 0, 3);
	
	SDL_GL_DeleteContext(gl_context);
	SDL_DestroyWindow(window);
}