Short SDL triangle example

sdl_hello_triangle.cpp

#define GL_GLEXT_PROTOTYPES 1
#include <SDL2/SDL.h>
#include <SDL2/SDL_opengles2.h>

int main() {
  auto window = SDL_CreateWindow(
    "triangle", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
    512, 512, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN
  );

  auto glcontext = SDL_GL_CreateContext(window);

  GLuint vbo = 0;
  glGenBuffers(1, &vbo);

  static const float vertices[] = { 0.0f, 0.5f, 0.5f, -0.5f, -0.5f, -0.5f };

  glBindBuffer(GL_ARRAY_BUFFER, vbo);
  glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

  auto vertexSource =
    "attribute vec4 pos;\n"
    "void main() { gl_Position = pos; }\n"
  ;

  GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
  glShaderSource(vertexShader, 1, &vertexSource, nullptr);
  glCompileShader(vertexShader);

  auto fragmentSource =
    "void main() { gl_FragColor = vec4(1, 0, 0, 1); }\n"
  ;

  GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
  glShaderSource(fragmentShader, 1, &fragmentSource, nullptr);
  glCompileShader(fragmentShader);

  GLuint shaderProgram = glCreateProgram();
  glAttachShader(shaderProgram, vertexShader);
  glAttachShader(shaderProgram, fragmentShader);
  glLinkProgram(shaderProgram);
  glUseProgram(shaderProgram);

  auto posAttr = glGetAttribLocation(shaderProgram, "pos");

  for(;;) {
    SDL_Event e;
    while(SDL_PollEvent(&e)) {
      if(e.type == SDL_QUIT) return 0;
    }

    glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glEnableVertexAttribArray(posAttr);
    glVertexAttribPointer(posAttr, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    SDL_GL_SwapWindow(window);
  }
}