//drawLine1
//showing two examples of the function drawLine()
//void drawLine(int x1, int y1, int x2, int y2)
// T. Kosaka CS TNCT 2001

#include <stdio.h>
#include <math.h>
#include <GL/glut.h>

void setColor(float red,float green,float blue)
{
    glColor3f(red, green, blue);    
}

void drawDot(int x,int y)
{
    glBegin(GL_POINTS);
        glVertex2i(x, y);
    glEnd();
}

/*
void drawLine(int x1, int y1, int x2, int y2)
{
    int i, len, width = x2 - x1, height = y2 - y1;
    int delta;
    float width_diff, height_diff;

    if(abs(width) > abs(height)) {
        len=abs(width);
        delta=width/len;
        height_diff = (float)height / (float)len;
        for(i = 0; i <= len; i++)
            drawDot((int)(x1 + i * delta), (int)(y1 + i * height_diff+0.5));
    } else {
        len=abs(height);
        delta=height/len;
        width_diff = (float)width / (float)len;
        for(i = 0; i <= len; i++)
            drawDot((int)(x1 + i * width_diff+0.5), (int)(y1 + i * delta));
    }
}
*/

void drawLine(int x1, int y1, int x2, int y2)
{
    int i, len, width = x2 - x1, height = y2 - y1;
    float width_diff, height_diff;

    if(abs(width) > abs(height)) len = abs(width);
    else len = abs(height);

    width_diff = (float)width / (float)len;
    height_diff = (float)height / (float)len;

    for(i = 0; i <= len; i++)
        drawDot((int)(x1 + i * width_diff+0.5), (int)(y1 + i * height_diff+0.5));
}

void userdraw(void);

void display(void)
{
    glClear( GL_COLOR_BUFFER_BIT);
    userdraw();
    glutSwapBuffers();
}

void userdraw(void)
{
    setColor(1,1,1);
    drawLine(320+20,240+10,320+200,240+100);
    drawLine(320+10,240+20,320+100,240+200);
    drawLine(320-10,240+20,320-100,240+200);
    drawLine(320-20,240+10,320-200,240+100);
    drawLine(320-20,240-10,320-200,240-100);
    drawLine(320-10,240-20,320-100,240-200);
    drawLine(320+10,240-20,320+100,240-200);
    drawLine(320+20,240-10,320+200,240-100);
}

int main(int argc, char **argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode ( GLUT_DOUBLE | GLUT_RGB );
    glutInitWindowPosition(100,100);
    glutInitWindowSize(640,480);
    glutCreateWindow ("Line 1");
    glClearColor(0.0, 0.0, 0.0, 0.0);
    gluOrtho2D(0., 640., 0.0, 480.0);
      // Define the dimensions of the Orthographic Viewing Volume
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}