// Forked from "intersect rect" by OiWeiWei
// https://turtletoy.net/turtle/7e326711bc

Canvas.setpenopacity(-1.0);

const t = new Turtle();

function clip_local(x1, y1, x2, y2, rx, ry, w, h) {
    let s_c = [];

    let iy1_t = (rx - x1) / (x2 - x1);
    let iy1 = y1 + (y2 - y1) * iy1_t;
    let iy1_in = (iy1 >= ry) && (iy1 <= ry + h) && (iy1_t >= 0) && (iy1_t <= 1);
    
    let iy2_t = (rx + w - x1) / (x2 - x1);
    let iy2 = y1 + (y2 - y1) * iy2_t;
    let iy2_in = (iy2 >= ry) && (iy2 <= ry + h) && (iy2_t >= 0) && (iy2_t <= 1);
    
    let ix1_t = (ry + h - y1) / (y2 - y1);
    let ix1 = x1 + (x2 - x1) * ix1_t;
    let ix1_in = (ix1 >= rx) && (ix1 <= rx + w) && (ix1_t >= 0) && (ix1_t <= 1);
    
    let ix2_t = (ry - y1) / (y2 - y1)
    let ix2 = x1 + (x2 - x1) * ix2_t;
    let ix2_in = (ix2 >= rx) && (ix2 <= rx + w) && (ix2_t >= 0) && (ix2_t <= 1);
    
    let p1_in = (x1 >= rx) && (x1 <= rx + w) && (y1 >= ry) && (y1 <= ry + h);
    
    let p2_in = (x2 >= rx) && (x2 <= rx + w) && (y2 >= ry) && (y2 <= ry + h);
    
    if (p1_in && p2_in) {
        // return nothing
    }
    else if (!iy1_in && !iy2_in && !ix1_in && !ix2_in) {
        s_c.push([x1, y1, x2, y2]);
    } 
    else if (p1_in && !p2_in) {
        if (iy1_in) {
            s_c.push([x2, y2, rx, iy1]);
        }

        if (iy2_in) {
            s_c.push([x2, y2, rx + w, iy2]);
        }
        
        if (ix1_in) {
            s_c.push([x2, y2, ix1, ry + h]);
        }
        
        if (ix2_in) {
            s_c.push([x2, y2, ix2, ry]);
        }
    }
    else if (!p1_in && p2_in) {
        if (iy1_in) {
            s_c.push([x1, y1, rx, iy1]);
        }

        if (iy2_in) {
            s_c.push([x1, y1, rx + w, iy2]);
        }
        
        if (ix1_in) {
            s_c.push([x1, y1, ix1, ry + h]);
        }
        
        if (ix2_in) {
            s_c.push([x1, y1, ix2, ry]);
        } 
    }
    else {
        if (iy1_in) {
            if (x1 <= rx) {
                s_c.push([x1, y1, rx, iy1]);
            }
            else {
                s_c.push([x2, y2, rx, iy1]);
            }
        }    
        
        if (iy2_in) {
            if (x2 > rx + w) {
                s_c.push([rx + w, iy2, x2, y2]);
            }
            else {
                s_c.push([rx + w, iy2, x1, y1]);
            }
        }
        
        if (ix1_in) {
            if (y2 > ry + h) {
                s_c.push([ix1, ry + h, x2, y2]);
            }
            else {
                s_c.push([ix1, ry + h, x1, y1]);
            }
        }
        
        if (ix2_in) {
            if (y1 < ry) {
                s_c.push([ix2, ry, x1, y1]);
            }
            else {
                s_c.push([ix2, ry, x2, y2]);
            }
        }
    } 
    
    return s_c;
}

function clip(x1, y1, x2, y2, rx, ry, ax, ay, w, h) {
    let x1_loc = (x1 - rx) * ax + (y1 - ry) * ay;
    let y1_loc = (x1 - rx) * (-ay) + (y1 - ry) * ax;
    let x2_loc = (x2 - rx) * ax + (y2 - ry) * ay;
    let y2_loc = (x2 - rx) * (-ay) + (y2 - ry) * ax;
    
    let sc = clip_local(x1_loc, y1_loc, x2_loc, y2_loc, 0, 0, w, h);
    
    for (let i = 0; i < sc.length; i++) {
        let cx1 = sc[i][0], cy1 = sc[i][1];
        sc[i][0] = cx1 * ax + cy1 * -ay + rx;
        sc[i][1] = cx1 * ay + cy1 * ax + ry;

        let cx2 = sc[i][2], cy2 = sc[i][3];
        sc[i][2] = cx2 * ax + cy2 * -ay + rx;
        sc[i][3] = cx2 * ay + cy2 * ax + ry;
    }
    
    return sc;
}

let pages = [];

function clip_pages(x1, y1, x2, y2) {
    let result = [[x1, y1, x2, y2]];
    
    for (let i = 0; i < pages.length; i++) {
        let rx = pages[i][0], ry = pages[i][1];
        let ax = pages[i][2], ay = pages[i][3];
        let w = pages[i][4], h = pages[i][5];
        
        let new_result = [];
        
        for (let j = 0; j < result.length; j++) {
            let cx1 = result[j][0], cy1 = result[j][1];
            let cx2 = result[j][2], cy2 = result[j][3];
            
            let sc = clip(cx1, cy1, cx2, cy2, rx, ry, ax, ay, w, h);
            
            for (let k = 0; k < sc.length; k++) {
                new_result.push(sc[k]);
            }
        }
        
        result = new_result;
    }
    
    return result;
}

function draw_clipped(x1, y1, x2, y2) {
    s_c = clip_pages(x1, y1, x2, y2);
    
    for (let j = 0; j < s_c.length; j++) {
        t.jump(s_c[j][0], s_c[j][1]);
        t.goto(s_c[j][2], s_c[j][3]);
    }
    
    return (s_c.length > 0);
}

function point_is_seen(px, py) {
    for (let i = 0; i < pages.length; i++) {
        let rx = pages[i][0], ry = pages[i][1];
        let ax = pages[i][2], ay = pages[i][3];
        let w = pages[i][4], h = pages[i][5];
    
        let px_loc = (px - rx) * ax + (py - ry) * ay;
        let py_loc = (px - rx) * (-ay) + (py - ry) * ax;
        
        if ((px_loc >= 0) && (px_loc <= w) && (py_loc >= 0) && (py_loc <= h)) {
            return false;
        } 
    }
    
    return true;
}

function draw_page(rx, ry, ax, ay, w, h) {
    const x1 = rx, y1 = ry;
    const x2 = x1 + ax * w, y2 = y1 + ay * w;
    const x3 = x2 - ay * h, y3 = y2 + ax * h;
    const x4 = x1 - ay * h, y4 = y1 + ax * h;

    let d1 = draw_clipped(x1, y1, x2, y2);
    let d2 = draw_clipped(x2, y2, x3, y3);
    let d3 = draw_clipped(x3, y3, x4, y4);
    let d4 = draw_clipped(x4, y4, x1, y1);
    
    let seen = d1 || d2 || d3 || d4;

    for (let y = 2; y < h - 2; y += 1) {
        for (let x = 2; x < w - 2; x += 1) {
            if (Math.random() < 0.5) {
                let px = rx + x * ax + y * -ay;
                let py = ry + x * ay + y * ax;
                
                if (point_is_seen(px, py)) {
                    t.jump(px, py);
                    t.goto(px + ax * 0.75, py + ay * 0.75);
                }
            }
        }
    }

    if (seen) {
        pages.push([rx, ry, ax, ay, w, h]);
    }
}

for (let i = 0; i < 600; i++) {
    let R = 10 + 131 * Math.random();
    let psi = 2 * Math.PI * Math.random();
    let rx = R * Math.cos(psi), ry = R * Math.sin(psi);
    
    // let rx = -100 + 200 * Math.random();
    // let ry = -100 + 200 * Math.random();
    
    let phi = Math.atan2(ry, rx);// + Math.PI * 0.1 * (-0.5 + Math.random());
    let ax = Math.cos(phi), ay = Math.sin(phi);
    
    let scale = 0.25 + 1.5 * Math.sqrt(rx * rx + ry * ry) / Math.sqrt(100*100*2);
    let w = 21 * scale, h = 29.7 * scale;

    draw_page(rx, ry, ax, ay, w, h);
}