Need help in printing fractal tree

问题

I need some help in printing fractal tree using JavaScript.

I have written code which prints tree sequence according to the rules defined for the tree, but having some trouble to print the tree. Thanks for all the help.

Here is the code:

var sentence = "F";
var rules = [];
rules[0] = {
    a: "F",
    b: "F[+F]F[-F]F"
}

setup();
function setup() {
    turtle();
    for (i = 0; i < 2; i++){
        generate();
    }
}

function turtle(){
    var canvas = document.getElementById("myCanvas");
    var context = canvas.getContext('2d');
    for (var i = 0; i < sentence.length; i++){
        context.beginPath();
        var current = sentence.charAt(i);
        if (current == "F"){
            context.stroke();
            context.lineTo(50,50);
        }else if (current == "+"){
            context.rotate(20*Math.PI/180);
        }else if (current == "-"){
            context.rotate(-20*Math.PI/180);
        }else if (current == "["){
            context.save();
        }else if (current == "]"){
            context.restore();
        }
    }
}

function generate(){
    var nextSentence = "";
    for (var i = 0; i < sentence.length; i++){
        var current = sentence.charAt(i);
        var found = false;
        for (var j = 0; j < rules.length; j++ ){
            if (current == rules[j].a){
                found = true;
                nextSentence += rules[j].b;
                console.log(nextSentence);
                break;
            }
        }
        if (!found){
            nextSentence += current;
        }
    }
    sentence = nextSentence;
    turtle();
}

I am able to print a tree sequence, but need some help in converting that tree sequence to be able to print a tree on the canvas. The output should look something like this:

回答1:

There are some issue with your drawing logic. You code seems to be assuming that save() and restore() also save the coordinates and restore them -- they don't. You aren't using rotate() correctly (it rotates relative to the origin so you need to also translate()). You're doing absolute lineto() when you should be doing it relative to the current position. And moving in the wrong direction. And other issues.

Here's my rework of your code to make it run just enough to produce the example tree:

var sentence = "F";
var rules = [];

rules[0] = {
    a: "F",
    b: "F[+F]F[-F]F"
}

var x = 150;  // starting x
var y = 400;  // starting y
var y_stack = [];  // save & restore don't handle coordinates

function turtle(sentence, context) {

    for (var i = 0; i < sentence.length; i++) {

        var current = sentence.charAt(i);

        if (current == "F") {
            y -= 35;
            context.lineTo(x, y);
            context.stroke();
        } else if (current == "+") {
            context.translate(x, y);
            context.rotate(20 * Math.PI / 180);
            context.translate(-x, -y);
        } else if (current == "-") {
            context.translate(x, y);
            context.rotate(-20 * Math.PI / 180);
            context.translate(-x, -y);
        } else if (current == "[") {
            context.save();
            y_stack.push(y);
        } else if (current == "]") {
            context.restore();
            y = y_stack.pop();
            context.moveTo(x, y)
        }
    }
}

function generate(sentence) {
    var nextSentence = "";

    for (var i = 0; i < sentence.length; i++) {
        var current = sentence.charAt(i);
        var found = false;

        for (var j = 0; j < rules.length; j++ ) {
            if (current == rules[j].a) {
                found = true;
                nextSentence += rules[j].b;
                break;
            }
        }

        if (!found) {
            nextSentence += current;
        }
    }

    return nextSentence;
}

function draw() {
    var canvas = document.getElementById("myCanvas");
    var context = canvas.getContext('2d');

    context.moveTo(x, y);

    for (i = 0; i < 2; i++) {
        sentence = generate(sentence);
    }

    console.log(sentence);
    turtle(sentence, context);

}

来源：https://stackoverflow.com/questions/49619855/need-help-in-printing-fractal-tree