javascript - 如何确定哪个 Canvas 对象首先完成其随机速度动画

Question

我是 Javascript 和 canvas 的新手。我正在开发一个简单的 Canvas 竞赛游戏，它随机设置两个矩形(红色和蓝色)的速度。我已经设置好了，所以它们都停在某个点。当一辆车获胜时，它会打印出“Red/Blue Won!”在 Canvas 上。

我已经把赛车部分写下来了，但我一直在想办法如何运行条件语句，把它放在哪里，并在 1 个矩形首先到达比赛终点/某个点时将其打印出来。

 if (square1 gets passed finish line first or stops moving)  {
    // Draw to canvas 
    context.font = "20pt sans-serif";
    context.fillText("Red is The Winner!", 5, 25, 300);
    context.fillStyle = "red";
  }
else if (square2 gets passed finish line first or stops moving) {

    context.font = "20pt sans-serif";
    context.fillText("Blue is The Winner!", 5, 280, 300);
    context.fillStyle = "blue";
}

我不确定这是否是我使用时间制作动画的方式。任何帮助将非常感激。

这是动画代码

  var animateRed = function(prop, val, duration) {
    // The calculations required for the step function
    var start = new Date().getTime();
    var end = start + duration;
    var current = square1[prop];
    var distance = val - current;

    var step = function() {
      // Get our current progres
      var timestamp = new Date().getTime();
      var progress = Math.min((duration - (end - timestamp)) / duration, 1);


      // Update the square's property
      square1[prop] = current + (distance * progress);
      // If the animation hasn't finished, repeat the step.
      if (progress < 1) requestAnimationFrame(step);
    };

    // Start the animation
    return step();
  };

  var animateBlue = function(prop, val, duration) {
    // The calculations required for the step function
    var start = new Date().getTime();
    var end = start + duration;
    var current = square2[prop];
    var distance = val - current;

    var step = function() {
      // Get our current progres
      var timestamp = new Date().getTime();
      var progress = Math.min((duration - (end - timestamp)) / duration, 1);


      // Update the square's property
      square2[prop] = current + (distance * progress);
      // If the animation hasn't finished, repeat the step.
      if (progress < 1) requestAnimationFrame(step);
    };

    // Start the animation
    return step();
  };


  $("#go").on('click', function() {
    //Math.floor(Math.random() * 1000) + 100;  
    var speedRed = Math.floor(Math.random() * 1000) + 500;
    var speedBlue = Math.floor(Math.random() * 1000) + 500;
    animateRed('x', 450, speedRed);
    animateBlue('x', 450, speedBlue);
  });

**************** 更新了 Fiddle ********************不小心发错了

这是我的 fiddle :Fiddle

Answer 1

您可以使用Promise.race()

var animateRed = function(prop, val, duration) {
        // The calculations required for the step function
        return new Promise(function(resolve) {
          var start = new Date().getTime();
          var end = start + duration;
          var current = square1[prop];
          var distance = val - current;
          // var speedRed = Math.floor(Math.random() * (90 - 20) + 20);
          //Math.floor(Math.random() * 2);


          var step = function() {
            // Get our current progres
            var timestamp = new Date().getTime();
            var progress = Math.min((duration - (end - timestamp)) / duration, 1);
            // Update the square's property
            square1[prop] = current + (distance * progress);
            // If the animation hasn't finished, repeat the step.
            if (progress < 1) {
              requestAnimationFrame(step)
            } else {
              resolve("red")
            }
          };

          // Start the animation
          step();
        })
      };

      var animateBlue = function(prop, val, duration) {
        // The calculations required for the step function
        return new Promise(function(resolve) {
          var start = new Date().getTime();
          var end = start + duration;
          var current = square2[prop];
          var distance = val - current;
          // var speedBlue = Math.floor(Math.random() * (90 - 20) + 20);

          var step = function() {
            // Get our current progres
            var timestamp = new Date().getTime();
            var progress = Math.min((duration - (end - timestamp)) / duration, 1);
            // Update the square's property
            square2[prop] = current + (distance * progress);
            // If the animation hasn't finished, repeat the step.
            if (progress < 1) {
              requestAnimationFrame(step)
            } else {
              resolve("blue")
            }
          };

          // Start the animation
          step();
        })
      };

      Promise.race([animateRed('x', 450, speedRed),
          animateBlue('x', 450, speedBlue)
        ])
        .then(function(winner) {
          alert(winner + " wins")
        });

var canvas = document.getElementById('canvas');
var goBtn = document.getElementById('go');
goBtn.addEventListener('click', render, false);

if (canvas.getContext) {
  // Grab our context
  var context = canvas.getContext('2d');

  // Make sure we have a valid defintion of requestAnimationFrame
  var requestAnimationFrame =
    window.requestAnimationFrame ||
    window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    window.oRequestAnimationFrame ||
    function(callback) {
      return setTimeout(callback, 16);
    };

  // Let's define our square
  var square1 = {
    'x': 0,
    'y': 50,
    'width': 50,
    'height': 50,
    'fill': '#FF0000'
  };

  // Let's define our square
  var square2 = {
    'x': 0,
    'y': 120,
    'width': 50,
    'height': 50,
    'fill': '#4169E1'
  };

  var render = function() {
    // Clear the canvas
    context.clearRect(0, 0, canvas.width, canvas.height);

    // Draw the square
    context.beginPath();
    context.rect(square1.x, square1.y, square1.width, square1.height);
    context.fillStyle = square1.fill;
    context.fill();

    // Draw the square
    context.beginPath();
    context.rect(square2.x, square2.y, square2.width, square2.height);
    context.fillStyle = square2.fill;
    context.fill();

    // Finish Line
    context.beginPath();
    context.strokeStyle = 'black';
    context.moveTo(canvas.width - 110, 0);
    context.lineTo(canvas.width - 110, 290);
    context.globalCompositeOperation = "destination-over";
    context.lineWidth = 10;
    context.stroke();

    /*
        context.font = "20pt sans-serif";
        context.fillText("Red is The Winner!", 5, 25, 300);
        context.fillStyle = '#FF0000';


        context.font = "20pt sans-serif";
        context.fillText("Blue is The Winner!", 5, 280, 300);
        context.fillStyle = "red";
    */
    // Redraw
    requestAnimationFrame(render);
  };

  // Start the redrawing process
  render();

  var animateRed = function(prop, val, duration) {
    // The calculations required for the step function
    return new Promise(function(resolve) {
      var start = new Date().getTime();
      var end = start + duration;
      var current = square1[prop];
      var distance = val - current;
      // var speedRed = Math.floor(Math.random() * (90 - 20) + 20);
      //Math.floor(Math.random() * 2);


      var step = function() {
        // Get our current progres
        var timestamp = new Date().getTime();
        var progress = Math.min((duration - (end - timestamp)) / duration, 1);
        // Update the square's property
        square1[prop] = current + (distance * progress);
        // If the animation hasn't finished, repeat the step.
        if (progress < 1) {
          requestAnimationFrame(step)
        } else {
          resolve("red")
        }
      };

      // Start the animation
      step();
    })
  };

  var animateBlue = function(prop, val, duration) {
    // The calculations required for the step function
    return new Promise(function(resolve) {
      var start = new Date().getTime();
      var end = start + duration;
      var current = square2[prop];
      var distance = val - current;
      // var speedBlue = Math.floor(Math.random() * (90 - 20) + 20);

      var step = function() {
        // Get our current progres
        var timestamp = new Date().getTime();
        var progress = Math.min((duration - (end - timestamp)) / duration, 1);
        // Update the square's property
        square2[prop] = current + (distance * progress);
        // If the animation hasn't finished, repeat the step.
        if (progress < 1) {
          requestAnimationFrame(step)
        } else {
          resolve("blue")
        }
      };

      // Start the animation
      step();
    })
  };

  if (animateRed() < animateBlue()) {
    context.font = "20pt sans-serif";
    context.fillText("Red is The Winner!", 5, 25, 300);
    context.fillStyle = '#FF0000';
  }

  //Math.floor(Math.random() * 1000) + 100;  
  var speedRed = Math.floor(Math.random() * 1000) + 500;
  var speedBlue = Math.floor(Math.random() * 1000) + 500;
  Promise.race([animateRed('x', 450, speedRed),
      animateBlue('x', 450, speedBlue)
    ])
    .then(function(winner) {
      alert(winner + " wins")
    });

};

canvas {
  border: 1px solid black;
}

<canvas width='500' height='300' id='canvas'>Your browser does not support canvas - go get Chrome!</canvas>

<button class="goBtn" id="go">Go</button>

jsfiddle https://jsfiddle.net/py49rzbu/