dda algorithm using OpenGL [duplicate] - opengl

Question

This question already has an answer here:
Compilation error with bresenham line algorithm?
(1 answer)
Closed 6 years ago.
Errors while compiling:
redefinition of 'y1' as different kind of symbol float x1 = 0, y1 = 0, x2 = 0, y2 = 0;
non-object type 'double (double)' is not assignable
y1 = 240-y;
no matching function for call to 'drawPixel'
drawPixel( x1, y1 );
no matching function for call to 'dda'
dda( x1, y1, x2, y2 );
Code:
#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif
#include <iostream>
using namespace std;
#include <cstdlib>
#include <cmath>
//defining constants
#define MAX_WIDTH 640
#define MAX_HEIGHT 480
int flag = 1;
float x1 = 0, y1 = 0, x2 = 0, y2 = 0;
//method for drawing the pixel
void drawPixel( int x, int y ){
glBegin( GL_POINTS );
//setting the pointer color
glColor3f( 1.0, 1.0, 1.0 );
glVertex2i( x, y );
glEnd();
glFlush();
}
//display callback function
void display(){
glClear( GL_COLOR_BUFFER_BIT );
gluLookAt( 0.0, 0.0, 0.0, 0.0, 0.0, 5.0, 0.0, 1.0, 0.0 );
/*
glBegin( GL_POINTS );
//setting the pointer color
glColor3f( 1.0, 1.0, 1.0 );
glVertex2i( 0, 0 );
glVertex2i( 10, 0 );
glEnd();
*/
glFlush();
}
//catching keyboard events
void keyboardEvent( unsigned char c, int x, int y ){
if( c == 27 ){
exit(0);
}
}
//dda implementation
void dda( float m1 , float n1 , float m2 , float n2 ){
float slope , Dx , Dy;
float dx , dy , length;
int i = 1;
dx = dy = length = 0.0;
slope = Dx = Dy = 0.0;
dx = m2 - m1;
dy = n2 - n1;
slope = dy/dx; //slope
cout << m1 << "\t" << n1 << "\t" << m2 << "\t" << n2 << endl;
length = (dx >= dy)?dx:dy ;
cout << length<< endl;
Dx = dx/length;
Dy = dy/length;
drawPixel( round(m1), round(n1) );
cout << m1 << m2 << endl;
for( ; i <= length ; i++ ){
m1 = m1 + Dx;
n1 = n1 + Dy;
drawPixel( round(m1), round(n1) );
cout << m1 << m2 << endl;
}
}
//catching mouse click events
void mouseEvent( int button, int state, int x, int y ){
//checking if the mouse button is clicked or not using state para.
if( state == GLUT_DOWN ){
if( button == GLUT_LEFT_BUTTON && flag == 1 ){
x1 = 320-x;
y1 = 240-y;
drawPixel( x1, y1 );
flag++;
}
else if( button == GLUT_LEFT_BUTTON && flag == 2 ){
x2 = 320-x;
y2 = 240-y;
drawPixel( x2, y2 );
flag++;
}
else if( button == GLUT_RIGHT_BUTTON && flag > 2 ){
drawPixel( 320-x, 240-y );
cout << x1 << "\t" << y1 << "\t" << x2 << "\t" << y2 << endl;
dda( x1, y1, x2, y2 );
}
}
}
//adjusting window when it is moved or resized
void reshape( int w, int h ){
glViewport( 0, 0, w, h );
}
//initialising the window at startup
void initialise(){
glClearColor( 0.0, 0.0, 0.0, 1.0 );
glPointSize( 5 );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluOrtho2D( -320, 320, -240, 240 );
}
int main( int argc, char **argv ){
//initialising the glut library
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
glutInitWindowSize( MAX_WIDTH, MAX_HEIGHT );
glutInitWindowPosition( 100, 100 );
glutCreateWindow("DDA Assignment");
//calling normal functions
initialise();
//registering callback functions
glutDisplayFunc( display );
glutKeyboardFunc( keyboardEvent );
glutMouseFunc( mouseEvent );
glutReshapeFunc( reshape );
glutMainLoop();
return 0;
}

Answer 1

If you compile this on POSIX, you will end up with <math.h> (and cmath) declaring functions with the name y0, y1 and yn, which will totally conflict with any global variable of the same name.
Since you explicitely tagged this question as c++14, you should also tell your compile to use that standard by using
g++ -std=c++14
(or any other appropriate version of the standard), which will also prevent the libc headers from declaring functions which are not in that standard.