klips/cpp/opengl-cmake/test-gl.cpp

/*#############################################################################
## Author: Shaun Reed                                                        ##
## Requires freeglut3-dev to be installed with your package manager          ##
## To build an executable: `g++ test-gl.cpp -w -lGL -lGLU -lglut -o test`    ##
##                                                                           ##
## Testing building OpenGL projects with source code from lazyfoo -          ##
## https://lazyfoo.net/tutorials/OpenGL/                                     ##
##############################################################################
## test-gl.cpp
*/

#include <GL/freeglut.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <stdio.h>

//Screen constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_FPS = 60;

//Color modes
const int COLOR_MODE_CYAN = 0;
const int COLOR_MODE_MULTI = 1;

//The current color rendering mode
int gColorMode = COLOR_MODE_CYAN;

//The projection scale
GLfloat gProjectionScale = 1.f;

bool initGL()
{
  //Initialize Projection Matrix
  glMatrixMode( GL_PROJECTION );
  glLoadIdentity();
  glOrtho( 0.0, SCREEN_WIDTH, SCREEN_HEIGHT, 0.0, 1.0, -1.0 );

  //Initialize Modelview Matrix
  glMatrixMode( GL_MODELVIEW );
  glLoadIdentity();

  //Initialize clear color
  glClearColor( 0.f, 0.f, 0.f, 1.f );

  //Check for error
  GLenum error = glGetError();
  if( error != GL_NO_ERROR )
  {
    printf( "Error initializing OpenGL! %s\n", gluErrorString( error ) );
    return false;
  }

  return true;
}

void update()
{

}

void render()
{
  //Clear color buffer
  glClear( GL_COLOR_BUFFER_BIT );

  //Reset modelview matrix
  glMatrixMode( GL_MODELVIEW );
  glLoadIdentity();

  //Move to center of the screen
  glTranslatef( SCREEN_WIDTH / 2.f, SCREEN_HEIGHT / 2.f, 0.f );

  //Render quad
  if( gColorMode == COLOR_MODE_CYAN )
  {
    //Solid Cyan
    glBegin( GL_QUADS );
    glColor3f( 0.f, 1.f, 1.f );
    glVertex2f( -50.f, -50.f );
    glVertex2f(  50.f, -50.f );
    glVertex2f(  50.f,  50.f );
    glVertex2f( -50.f,  50.f );
    glEnd();
  }
  else
  {
    //RYGB Mix
    glBegin( GL_QUADS );
    glColor3f( 1.f, 0.f, 0.f ); glVertex2f( -50.f, -50.f );
    glColor3f( 1.f, 1.f, 0.f ); glVertex2f(  50.f, -50.f );
    glColor3f( 0.f, 1.f, 0.f ); glVertex2f(  50.f,  50.f );
    glColor3f( 0.f, 0.f, 1.f ); glVertex2f( -50.f,  50.f );
    glEnd();
  }

  //Update screen
  glutSwapBuffers();
}

void handleKeys( unsigned char key, int x, int y )
{
  //If the user presses q
  if( key == 'q' )
  {
    //Toggle color mode
    if( gColorMode == COLOR_MODE_CYAN )
    {
      gColorMode = COLOR_MODE_MULTI;
    }
    else
    {
      gColorMode = COLOR_MODE_CYAN;
    }
  }
  else if( key == 'e' )
  {
    //Cycle through projection scales
    if( gProjectionScale == 1.f )
    {
      //Zoom out
      gProjectionScale = 2.f;
    }
    else if( gProjectionScale == 2.f )
    {
      //Zoom in
      gProjectionScale = 0.5f;
    }
    else if( gProjectionScale == 0.5f )
    {
      //Regular zoom
      gProjectionScale = 1.f;
    }

    //Update projection matrix
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glOrtho( 0.0, SCREEN_WIDTH * gProjectionScale, SCREEN_HEIGHT * gProjectionScale, 0.0, 1.0, -1.0 );
  }
}

void runMainLoop( int val );
/*
Pre Condition:
 -Initialized freeGLUT
Post Condition:
 -Calls the main loop functions and sets itself to be called back in 1000 / SCREEN_FPS milliseconds
Side Effects:
 -Sets glutTimerFunc
*/

int main( int argc, char* args[] )
{
  //Initialize FreeGLUT
  glutInit( &argc, args );

  //Create OpenGL 2.1 context
  glutInitContextVersion( 2, 1 );

  //Create Double Buffered Window
  glutInitDisplayMode( GLUT_DOUBLE );
  glutInitWindowSize( SCREEN_WIDTH, SCREEN_HEIGHT );
  glutCreateWindow( "OpenGL" );

  //Do post window/context creation initialization
  if( !initGL() )
  {
    printf( "Unable to initialize graphics library!\n" );
    return 1;
  }

  //Set keyboard handler
  glutKeyboardFunc( handleKeys );

  //Set rendering function
  glutDisplayFunc( render );

  //Set main loop
  glutTimerFunc( 1000 / SCREEN_FPS, runMainLoop, 0 );

  //Start GLUT main loop
  glutMainLoop();

  return 0;
}

void runMainLoop( int val )
{
  //Frame logic
  update();
  render();

  //Run frame one more time
  glutTimerFunc( 1000 / SCREEN_FPS, runMainLoop, val );
}