javascript - 使用箭头键旋转 Canvas 形状

Question

我希望使用左箭头键和右箭头键分别顺时针和逆时针旋转我的 Canvas 形状。目前该形状仅线性移动。

从长远来看，我试图使用这段javascript代码复制我的ROS(机器人操作系统)TurtleSim的运动，并且左右键以这种方式旋转turtlesim。 (我对 javascript 还很陌生。)

<script>
function Parent(){
    //diffColor = false;
    mainCanvas.load();
    tracker = new track(30, 50, "white", 30, 120); //create object that will move with keys;

    click();
    //touch();
    //animate();
    //mapCanvas.load();
}

function click(){
        window.addEventListener("click", getClickPosition, false);

    function getClickPosition(e){
        tracker.distanceX = e.clientX - (tracker.width / 2); //move tracker to near center of tracker; clientX gets horizontal coordinate of cursor
        tracker.distanceY = e.clientY - (tracker.height / 2);

        }
}


var mainCanvas = {
    canvas : document.createElement("canvas"),
    load: function(){

        this.canvas.width = (window.innerWidth)/2;
        this.canvas.height = window.innerHeight;
        this.ctx1 = this.canvas.getContext("2d");

        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.interval = setInterval(moveTracker, 20);

        window.addEventListener ("keydown", function(e){
            console.log(e.keyCode);
            mainCanvas.key = e.keyCode; //execute movement when key pressed
        });
        window.addEventListener ("keyup", function(e){
                mainCanvas.key = false; //stop movement once key is released
                });

    },

    clear: function(){
        this.ctx1.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

    function track(width, height, color, distanceX, distanceY, theSquare){ 
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;
    this.distanceX = distanceX;
    this.distanceY = distanceY;
    this.rotationSpeedRight = 0;
    this.rotationSpeedLeft= 0;
    this.rotationLeft = rotationLeft;
    this.rotationRight = rotationRight;
    console.log("inside track()");

    this.update = function(theSquare){
        ctx = mainCanvas.ctx1;
        ctx.fillStyle = color;
        ctx.fillRect(this.distanceX, this.distanceY, this.width, this.height, this.rotationLeft, this.rotationRight);
        ctx.rotate(45*Math.PI/180);
        ctx.save();
        ctx.restore();
    }
    this.newPosition = function(){
    this.rotation += this.rotationSpeed;
    this.distanceX += this.speed * Math.cos(this.rotation);
    this.distanceY += this.speed * Math.sin(this.rotation);
    }
}

function moveTracker(){ //recognize keys from keyboard
    mainCanvas.clear();
    tracker.speedX = 0;
    tracker.speedY = 0;
    tracker.rotationSpeedRight = 0;
    tracker.rotationSpeedLeft = 0;
    if (mainCanvas.key && mainCanvas.key == 37) //left key; should move anticlockwise
        tracker.rotationSpeedLeft = -1;
    if (mainCanvas.key && mainCanvas.key == 38) //down key
        tracker.speedY = -1;
    if (mainCanvas.key && mainCanvas.key == 39) //right key; should move clockwise;
        tracker.rotationSpeedRight = 1;
    if (mainCanvas.key && mainCanvas.key == 40) //up key
        tracker.speedY=1;

    tracker.newPosition();
    tracker.update();
}

Answer 1

不存在“左旋转”和“右旋转”之类的东西，它们指的是同一件事。您只需要一个旋转值，它就是绘图的当前 Angular 。

我还假设您希望向上键朝您面向的任何方向移动，而不是始终向上，因此您也可以将速度值切换为仅一个值，即当前方向的速度。这基本上改变了你的坐标系 cartesian (x, y) 至polar ( Angular 和距离)。
要了解基于旋转和速度的移动在 X-Y 平面上的最终变化，您必须对 X 使用 speed * cos(angle) 和 speed * sin(angle) > 对于 Y(基于三 Angular 学)。

在绘制矩形之前需要调用

rotate (这基本上是说“我接下来要做的所有事情都需要旋转该量”)并保存和 restore 需要围绕所有这些调用，以在完成绘制旋转形状后取消旋转。

另一个注意事项:rotate 围绕原点 (0, 0) 旋转 Canvas 。要围绕元素的中心旋转(这可能是您想要做的)，您需要首先翻译到该位置，然后不要忘记偏移您绘制矩形的位置考虑到初始翻译。

代码底部的潜在更新将是:

function track(width, height, color, distanceX, distanceY, rotation){
    this.width = width;
    this.height = height;
    this.distanceX = distanceX || 0;
    this.distanceY = distanceY || 0;
    this.speed = 0;
    this.rotation = rotation || 0;
    this.rotationSpeed = 0;

    this.update = function(){
        ctx = mainCanvas.ctx1;
        ctx.fillStyle = color;
        ctx.save();
        ctx.translate(this.distanceX, this.distanceY);
        ctx.rotate(this.rotation);
        ctx.fillRect(-this.width / 2, -this.height / 2, this.width, this.height);
        ctx.restore();
    }
    this.newPosition = function(){
        this.rotation += this.rotationSpeed;
        this.distanceX += this.speed * Math.cos(this.rotation);
        this.distanceY += this.speed * Math.sin(this.rotation);
    }
}

function moveTracker(){ //recognize keys from keyboard
    mainCanvas.clear();
    tracker.speed = 0;
    tracker.rotationSpeed = 0;
    // Adjust the values as you need here
    if (mainCanvas.key == 37) //left key
        tracker.rotationSpeed = -0.5 / Math.PI;
    if (mainCanvas.key == 38) //up key
        tracker.speed = 3;
    if (mainCanvas.key == 39) //right key
        tracker.rotationSpeed = 0.5 / Math.PI;
    if (mainCanvas.key == 40) //down key
        tracker.speed = -3;

    tracker.newPosition();
    tracker.update();
}

JSFiddle (粗略版)