OpenGL Odd Row Fragment Shader

odd-row-shader.cpp

#include <iostream>
#include <stdio.h>


//This is nice: http://stackoverflow.com/questions/3907818/opengl-headers-for-os-x-linux
//OS X headers
#ifdef __APPLE__
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#include <GLUT/glut.h>
#else
//Windows Headers
#ifdef _WIN32
  #include <windows.h>
#endif
//Regular Linux Headers
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#endif


void DrawGLScene(){
  glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

  // Draw some points
  glBegin(GL_TRIANGLES);
  glColor3f(0.1, 0.2, 0.3);
  glVertex3f(0, 0, 0);
  glVertex3f(1, 0, 0);
  glVertex3f(0, 1, 0);
  glEnd();

  glFlush();
  glutSwapBuffers();
}


void Shading(){
  //Fragment shader we want to use
  GLuint oddRowShaderId = glCreateShader(GL_FRAGMENT_SHADER);
  std::cout << "Creating the fragment shader with id " << oddRowShaderId << std::endl;

  const GLchar *source = 
    "void main(){   \n"
    "  if (mod(gl_FragCoord.y-0.5, 2.0) == 0.0){\n"
    "    gl_FragColor = vec4( 0.0, 1.0, 0.0, 1.0 );\n"
    "  }\n"
    "}\n\n";

  std::cout << "Shader source:\n" << source << std::endl;

  std::cout << "Gathering shader source code" << std::endl;
  glShaderSource(oddRowShaderId, 1, &source, NULL);
  std::cout << "Compiling the shader" << std::endl;
  glCompileShader(oddRowShaderId);

  GLint params;
  glGetShaderiv(oddRowShaderId, GL_COMPILE_STATUS, &params);
  if(params){
    std::cout << "Compiled Successfully" << std::endl;
  } else {
    std::cout << "Errors compiling" << std::endl;
    GLchar infoLog[256];
    int infoLogLength = 0;
    glGetShaderInfoLog(oddRowShaderId, 256, &infoLogLength, infoLog);
    std::cout << "Info Log: " << std::endl << infoLog << std::endl;
  }

  std::cout << "Creating new glCreateProgram() program" << std::endl;
  GLuint shaderProgramId = glCreateProgram();    //Shader program id
  std::cout << "Attaching shader to the new program" << std::endl;
  glAttachShader(shaderProgramId, oddRowShaderId); //Add the fragment shader to the program
  std::cout << "Linking the program " << std::endl;
  glLinkProgram(shaderProgramId);                //Link the program

  GLint err;
  glGetProgramiv(shaderProgramId, GL_LINK_STATUS, &err);
  if(err){
    std::cout << "Linked Successfully" << std::endl;
  } else {
    std::cout << "Errors Linking" << std::endl;
    GLchar errors[256];
    int errLength;
    glGetProgramInfoLog(shaderProgramId, 256, &errLength, errors);
    std::cout << "Program Error Log: " << std::endl << errors << std::endl;
  }

  std::cout << "Using the shader program for rendering" << std::endl;
  glUseProgram(shaderProgramId);                  //Start using the shader
}

void keyboard(int key, int x, int y){
  switch(key){
  case 's':
    Shading();
    break;
  case 'q':
    exit(0);
    break;
  }

}

void idleFunc(){
  glutPostRedisplay();        //Redraw the scene.
}

int main(int argc, char** argv){
  glutInit(&argc, argv);
  glutInitWindowPosition(100, 100);
  glutInitWindowSize(1000,1000);
  glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
  glutCreateWindow("anaglyph test");
  glutDisplayFunc(DrawGLScene);
  glutSpecialFunc(keyboard);
  glutIdleFunc(idleFunc);

  glutMainLoop();
}

Updated on 5/19/2016. Fixed a bunch of issues from back when I didn't really know C++.

Can successfully compile on OSX 10.11 with the following command:

> clang++ -framework OpenGL -framework GLUT -Wno-deprecated-declarations odd-row-shader.cpp