CG: DDA e Bresenham OPENGL

/* gcc -o file file.c -lglut -lGL -lGLU */

#include <GL/glut.h>

int abs(int n) { return n > 0 ? n : -n; }
int rnd(float n) { return (int) (n + 0.5); }

void display();
void drawLineBres(int xa, int ya, int xb, int yb, int inverted);
void drawLineDDA(int xa, int ya, int xb, int yb);
void drawLine(int xa, int ya, int xb, int yb, int reversed);

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(800, 480);
    int windowID = glutCreateWindow("a0307");
    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

void display()
{
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-50, 50, -50, 50);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glBegin(GL_POINTS);
        glColor3d(1, 0, 0);
        glVertex2d(0, 0);
        glVertex2d(0, 30);
        drawLineBres(10, 0, 25, 5, 0);
        drawLineDDA(20, 0, 35, 5);
        drawLine(30, 0, 45, 5, 0);
    glEnd();

    glFlush();
}

void drawLineBres(int xa, int ya, int xb, int yb, int inverted)
{
    int dx = xb - xa,
        dy = yb - ya,
        slope;

    if (xa > xb)
        return drawLineBres(xb, yb, xa, ya, inverted);
    if (abs(dy) > abs(dx))
        return drawLineBres(ya, xa, yb, xb, ! inverted);

    if (dy < 0)
    {
        slope = -1;
        dy = -dy;
    }
    else slope = 1;

    int incE = 2 * dy,
        incNE = 2 * (dy - dx),
        p = 2 * dy - dx;

    for (; xa <= xb; xa++)
    {
        if (inverted)
            glVertex2d(ya, xa);
        else
            glVertex2d(xa, ya);

        if (p < 0)
            p += incE;
        else {
            p += incNE;
            ya += slope;
        }
    }
}


void drawLineDDA(int xa, int ya, int xb, int yb)
{
    int dx = xb - xa,
        dy = yb - ya;

    int steps = abs(dx) > abs(dy) ? abs(dx) : abs(dy);

    float   xIncrement = dx / (float) steps,
            yIncrement = dy / (float) steps,
            x = xa,
            y = ya;

    glVertex2d(rnd(x), rnd(y));

    for (int k = 0; k < steps; k++)
    {
        x += xIncrement;
        y += yIncrement;

        glVertex2d(rnd(x), rnd(y));
    }
}

void drawLine(int xa, int ya, int xb, int yb, int reversed)
{
    int dx = xb - xa,
        dy = yb - ya;

    if (dx < 0)
        drawLine(xb, yb)

    if (abs(dx) >= abs(dy))
    {
        double  m = (double) (yb - ya) / (xa - xb);

        for (; dx > 0 ? xb > xa : xb < xa; xa += xInc)
        {
            if (reversed)
                glVertex2d((int) y, xa);
            else
                glVertex2d(xa, (int) y);

            y += yInc;
        }

        if (reversed)
            glVertex2d((int) y, xa);
        else
            glVertex2d(xa, (int) y);
    }
    else return drawLine(ya, xa, yb, xb, ! reversed);
}