Drawing a line with GLUT - c

Question

I have the next code using OPENGL GLUT, this code draws a line at a cursor position. Once you click the right button of the mouse it captures the coordinates x0, y0 of the line, then when the mouse moves to another pixel while pushing the button the coordinates(x1,y1) change, and finally when the button is released the line is drawn.
#include<windows.h>
#include <gl/glut.h>
float a[90000];
int x0=0,y0=0,xf=0,yf=0;
int print=0;
void init(void)
{
glClearColor(1.0, 1.0, 1.0, 0.0);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(0.0, 300.0, 0.0,300.0);
}
void putpixel(int x,int y)
{
glColor3f(0.0, 0.9,0.7);
glBegin(GL_POINTS);
glVertex2i(x,y);
glEnd();
}
void Bresenham(int x0, int y0, int x1, int y1)
{
int dx,dy,p,x,y,px = 1,py = 1,twoDy_Dx,twoDy,i;
glColor3f(0.0,0.0,1.0);
dx = x1-x0;
dy = y1-y0;
if(dx < 0)
dx = dx*-1;
if(dy < 0)
dy = dy*-1;
if(x1 < x0)
px = -1;
if(y1 < y0)
py = -1;
x = x0;
y = y0;
if( dx > dy )
{
putpixel(x,y);
p = 2 * dy - dx;
twoDy_Dx = 2 * ( dy - dx );
twoDy = 2 * dy;
for( i = 0; i < dx; i++ )
{
if( p >= 0 )
{
y += py;
p += twoDy_Dx;
}
else
p += twoDy;
x += px;
putpixel(x,y);
}
}
else
{
putpixel(x,y);
p = 2*dx - dy;
twoDy_Dx = 2 * ( dx - dy );
twoDy = 2*dx;
for( i = 0; i < dy; i++ )
{
if( p >= 0 )
{
x += px;
p += twoDy_Dx;
}
else
p += twoDy;
y += py;
putpixel(x,y);
}
}
glFlush();
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
if(print==1)
glDrawPixels(300,300,GL_RGB,GL_UNSIGNED_BYTE,a);
Bresenham(x0,y0,xf,yf);
glutSwapBuffers();
glFlush();
}
void onMotion(int x,int y)
{
xf=x;
yf=300-y;
glutPostRedisplay();
}
void onMouse(int button, int e, int x, int y)
{
if((button == GLUT_LEFT_BUTTON) && (e == GLUT_DOWN))
{
x0 = x;
y0 = abs(300-y);
print = 1;
}
if( (button == GLUT_RIGHT_BUTTON) && (e==GLUT_DOWN))
{
print=0;
}
if ( (button == GLUT_LEFT_BUTTON || button == GLUT_RIGHT_BUTTON) && (e == GLUT_UP) )
{
print=0;
}
}
void onPassive(int x,int y)
{
x0=-1;y0=-1;xf=-1;yf=-1;
glReadPixels( 0.0, 0.0,300.0,300.0,GL_RGB,GL_UNSIGNED_BYTE,a);
}
int main(int argc, char** argv)
{
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowPosition(100, 100);
glutInitWindowSize(300, 300);
glutCreateWindow("Line");
init();
glutDisplayFunc(display);
glutMotionFunc(onMotion);
glutMouseFunc(onMouse);
glutPassiveMotionFunc(onPassive);
glutMainLoop();
}
The problem that I have is that when the button is pushed and while the final coordinates are changing, the line should be drawn as a pointed line: ---------
but when it reaches the final coordinates, the line should be drawn like this: _________. How can I do this?