#include <stdio.h>
#include <stdint.h>
#include <assert.h>
#include <math.h>
#include <GL/freeglut.h>

#define WindowW 800
#define WindowH 600
#define FbW 320
#define FbH 240
#define FbTexW 0x200
#define FbTexH 0x100
static const float VertexCoord[] = {0, 0, FbTexW, 0, 0, FbTexH, FbTexW, FbTexH};

static void initGl() {
  glEnable(GL_TEXTURE_2D);
  glEnableClientState(GL_VERTEX_ARRAY);
  glClearColor(0, 0, 0, 0);
  glShadeModel(GL_FLAT);
  glOrtho(0, FbW, FbH, 0, 1, -1);
  glVertexPointer(2, GL_FLOAT, 0, VertexCoord);
}

static void resize(int w, int h) {
  int p = w * FbH;
  int q = h * FbW;
  if (p > q) {
    float w_ = (float)q / FbH;
    glViewport((int)roundf((w - w_) * 0.5f), 0, (int)roundf(w_), h);
  } else {
    float h_ = (float)p / FbW;
    glViewport(0, (int)roundf((h - h_) * 0.5f), w, (int)roundf(h_));
  }
}

static void draw() {
  glClear(GL_COLOR_BUFFER_BIT);
  glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
  glutSwapBuffers();
}

int main(int argc, char **argv) {
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE);
  glutInitWindowSize(WindowW, WindowH);
  glutCreateWindow(argv[0]);
  initGl();
  glutDisplayFunc(draw);
  glutReshapeFunc(resize);
  glutMainLoop();
  return 0;
}