#include<stdio.h>
#include<GL/glut.h>
#define MAXY 400
float x1, y1, x2, y2, x3, y3, x4, y4;
float le[MAXY], re[MAXY];
void myInit() {
    glClearColor(1.0, 1.0, 1.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, MAXY, 0, MAXY);
    glMatrixMode(GL_MODELVIEW);
}
void drawPoint(float x, float y) {
    glBegin(GL_POINTS);
    glVertex2f(x, y);
    glEnd();
    glFlush();
}
void edgeDetect(float x1, float y1, float x2, float y2) {
    if (y2<y1) {
        float temp = x2; x2=x1; x1=temp;
        temp=y2; y2=y1; y1=temp;
    }
    float mx;
    if (y2-y1 == 0)
        mx = x2-x1;
    else
        mx=(x2-x1)/(y2-y1);
    int x=x1;
    for (int i=y1; i<=y2; i++) {
        if (x<le[i])
            le[i] = x;
        if (x>re[i])
            re[i] = x;
        x+=mx;
    }
}
void scanfill() {
    for (int i=0; i<MAXY; i++) {
        le[i] = MAXY;
        re[i] = 0;
    }
    edgeDetect(x1, y1, x2, y2);
    edgeDetect(x2, y2, x3, y3);
    edgeDetect(x3, y3, x4, y4);
    edgeDetect(x4, y4, x1, y1);
    for (int y=100; y<300; y++) {
        for (int x=le[y]; x<=re[y]; x++) {
            drawPoint(x, y);
        }
    }
}
void display() {
    x1=200; y1=100; x2=100; y2=200; x3=200; y3=300; x4=300; y4=200;
}
void menu(int c) {
    switch (c) {
        case 1:
            glColor3f(0.0, 0.0, 1.0);
            glBegin(GL_LINE_LOOP);
            glVertex2f(x1, y1);
            glVertex2f(x2, y2);
            glVertex2f(x3, y3);
            glVertex2f(x4, y4);
            glEnd();
            glFlush();
            break;
        case 2:
            glColor3f(0.0, 0.0, 1.0);
            glBegin(GL_LINE_LOOP);
            glVertex2f(x1, y1);
            glVertex2f(x2, y2);
            glVertex2f(x3, y3);
            glVertex2f(x4, y4);
            glEnd();
            glFlush();
            scanfill();
            break;
    }
}
int main(int argc, char* argv[]) {
    glutInit(&argc, argv);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(500, 500);
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
    glutCreateWindow("Lab 9");
    myInit();
    glutCreateMenu(menu);
    glutDisplayFunc(display);
    glutAddMenuEntry("Draw Polygon", 1);
    glutAddMenuEntry("Fill Polygon", 2);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
    glutMainLoop();
    return 0;
}