main.c

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


void renderSpacedBitmapString(float x, float y, void *font, char *string) {
    char *c;
    int x1 = x;
    for (c = string; *c != '\0'; c++) {
        glRasterPos2f(x1, y);
        glutBitmapCharacter(font, *c);
        x1 = x1 + glutBitmapWidth(font, *c);
    }
}


void markString(char *string, int x, int y, int x_offset, int y_offset) {
    glColor3f(255.0, 0, 0.0); // red color
    renderSpacedBitmapString(x+x_offset, y+y_offset, GLUT_BITMAP_HELVETICA_12, string);
    glFlush();
}


void plotDivisionLines()    {
    glBegin(GL_LINES);
    glVertex2d(-320, 0);
    glVertex2d(320, 0);
    glVertex2d(0, -240);
    glVertex2d(0, 240);
    glEnd();
}


void plotPoint(int x, int y, int x_offset, int y_offset)    {
    glBegin(GL_POINTS);
    glVertex2d(x + x_offset, y + y_offset);
    glEnd();
}


void plotLine(int start_x, int start_y, int end_x, int end_y)   {
    glBegin(GL_LINES);
    glVertex2d(start_x, start_y);
    glVertex2d(end_x, end_y);
    glEnd();
}


void plotAtAllOctants(int x, int y, int x_offset, int y_offset) {
    plotPoint(x, y, x_offset, y_offset);
    plotPoint(y, x, x_offset, y_offset);
    plotPoint(x, -y, x_offset, y_offset);
    plotPoint(y, -x, x_offset, y_offset);
    plotPoint(-x, y, x_offset, y_offset);
    plotPoint(-y, x, x_offset, y_offset);
    plotPoint(-x, -y, x_offset, y_offset);
    plotPoint(-y, -x, x_offset, y_offset);
}


void plotCircle(int center_x, int center_y, int radius) {
    int x_k = 0;
    int y_k = radius;
    int p_k = 1 - radius;
    
    plotPoint(center_x, center_y, 0, 0);
    plotAtAllOctants(x_k, y_k, center_x, center_y);
    while(x_k <= y_k)   {
        if(p_k < 0) {
            plotAtAllOctants(x_k + 1, y_k, center_x, center_y);
            x_k += 1;
            p_k += (2*x_k) + 1;
        }
        else{
            plotAtAllOctants(x_k + 1, y_k - 1, center_x, center_y);
            x_k += 1;
            y_k += -1;
            p_k += (2*x_k) - (2*y_k) + 1;
        }
    }
}


void display_figure()   {
    glClear(GL_COLOR_BUFFER_BIT);
    plotCircle(0, 110, 30);
    plotCircle(0, 20, 60);
    // right-limb 1
    plotLine(60, 40, 110, 20);
    plotLine(110, 20, 140, 40);
    // left-limb 1
    plotLine(-60, 40, -110, 20);
    plotLine(-110, 20, -140, 40);
    // right-limb 2
    plotLine(60, 0, 110, -20);
    plotLine(110, -20, 140, 0);
    // left-limb 2
    plotLine(-60, 0, -110, -20);
    plotLine(-110, -20, -140, 0);
    // right-limb 3
    plotLine(40, -30, 90, -50);
    plotLine(90, -50, 120, -35);
    // left-limb 3
    plotLine(-40, -30, -90, -50);
    plotLine(-90, -50, -120, -35);
    // right-antenna
    plotLine(15, 140, 30, 180);
    // left-antenna
    plotLine(-15, 140, -30, 180);
    glFlush();
}


void display_circle()   {
    glClear(GL_COLOR_BUFFER_BIT);
    plotDivisionLines();

    plotCircle(0, 0, 80);
    markString("C(0,0); R80", 0, 0, 5, 5);
    
    glColor3f(0.0f, 0.0f, 0.0f);
    plotCircle(160, 120, 40);
    markString("C(160,120); R40", 160, 120, 5, 5);
    glFlush();
}


void init() {
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glColor3f(0.0f, 0.0f, 0.0f);
    glPointSize(4);
    glLineWidth(4);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-320.0, 320.0, -240.0, 240.0);
}


int main(int argc, char **argv)  {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(640, 480);

    // circle
    // glutCreateWindow("Ex4a - Midpoint Circle");
    // glutDisplayFunc(display_circle);
    
    // figure
    glutCreateWindow("Ex4b - Figure with Circles");
    glutDisplayFunc(display_figure);

    init();
    glutMainLoop();    
    return 1;
}