Attribute-less rendering with openGL - you're not allowed to draw with the default VertexArray so you need to create one.

Oils.cpp

#include <assert.h>
#include <roxlu/core/Log.h>
#include "Oils.h"

Oils::Oils() 
  :win_w(0)
  ,win_h(0)
  ,br_prog(0)
  ,br_vert(0)
  ,br_frag(0)
  ,br_vao(0)
{
}

Oils::~Oils() {
}

bool Oils::setup(int winW, int winH) {
  assert(winW);
  assert(winH);
  assert(br_prog == 0);

  win_w = winW;
  win_h = winH;

  br_vert = glCreateShader(GL_VERTEX_SHADER); glShaderSource(br_vert, 1, &OS_VS,NULL); glCompileShader(br_vert); eglGetShaderInfoLog(br_vert);
  br_frag = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(br_frag, 1, &OS_FS,NULL); glCompileShader(br_frag); eglGetShaderInfoLog(br_frag);
  br_prog = glCreateProgram(); glAttachShader(br_prog,br_vert); glAttachShader(br_prog,br_frag); glLinkProgram(br_prog); eglGetShaderLinkLog(br_prog);
  glUseProgram(br_prog);

  float pm[16] = { 0 };
  rx_ortho_top_left(win_w, win_h, -1.0f, 1.0f, pm);
  
  GLint u_pm = glGetUniformLocation(br_prog, "u_pm");
  glUniformMatrix4fv(u_pm, 1, GL_FALSE, pm);

  glGenVertexArrays(1, &br_vao);
  return true;
}


void Oils::draw() {
  glUseProgram(br_prog);
  glBindVertexArray(br_vao);
  glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

Oils.h

#ifndef ROXLU_OILS_H
#define ROXLU_OILS_H

#include <glr/GL.h>
#include <roxlu/math/Random.h>
#include <roxlu/math/Vec2.h>
#include <roxlu/opengl/GL.h>
#include <roxlu/opengl/Error.h>

using namespace roxlu;
using namespace gl;

static const char* OS_VS = ""
  "#version 150\n"
  "uniform mat4 u_pm;"
  "const float w = 40.0;"
  "const float h = 100.0;"

  "const vec2 data[4] = vec2[] ("
  "     vec2(-w,  h), "
  "     vec2(-w, -h), "
  "     vec2( w,  h), "
  "     vec2( w, -h) "
  ");"

  "void main() {"
  "   gl_Position = u_pm * vec4(data[gl_VertexID], 0.0, 1.0);"
  "}"
  "";

static const char* OS_FS = ""
  "#version 150\n"
  "out vec4 fragcolor;"

  "void main() {"
  "  fragcolor = vec4(1.0); "
  "}"
  "";

class Oils {
 public:
  Oils();
  ~Oils();
  bool setup(int winW, int winH);
  void draw();
 public:
  int win_w;
  int win_h;
  GLuint br_prog;
  GLuint br_vert;
  GLuint br_frag;
  GLuint br_vao;
};

#endif