在一张画布上绘制多个图像

Question

我有一个数组，其中包含有关如何绘制图像的所有信息。我想绘制 2 个图像，当我这样做时，它只绘制最后一个图像。我能做些什么？

for(i = 0; i < tiles.length; i++)
{
    var sourceX = tiles[i][5];
    var sourceY = tiles[i][6];
    var sourceWidth = tiles[i][9];
    var sourceHeight = tiles[i][10];
    var destWidth = sourceWidth;
    var destHeight = sourceHeight;
    var destX = tiles[i][7];
    var destY = tiles[i][8];

    var imageObj = new Image();
    imageObj.onload = function()
    {
        context.drawImage(imageObj, sourceX, sourceY, sourceWidth, sourceHeight, destX, destY, destWidth, destHeight);
    };
    imageObj.src = tiles[i][4];
}

Answer 1

let img = new Image();
  img.crossOrigin = 'Anonymous';
  const createCanvas = async (imageSrc) => {
      img.src = imageSrc;
      await img.decode();
      context.drawImage(img, x, y, sw, sh)    
  }

Answer 2

我无法解释更具体的原因，但这是我找到的解决方案。这对我有用。

const getContext = () => document.getElementById('my-canvas').getContext('2d');

// It's better to use async image loading.
const loadImage = url => {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => resolve(img);
    img.onerror = () => reject(new Error(`load ${url} fail`));
    img.src = url;
  });
};

// Here, I created a function to draw image.
const depict = options => {
  const ctx = getContext();
  // And this is the key to this solution
  // Always remember to make a copy of original object, then it just works :)
  const myOptions = Object.assign({}, options);
  return loadImage(myOptions.uri).then(img => {
    ctx.drawImage(img, myOptions.x, myOptions.y, myOptions.sw, myOptions.sh);
  });
};

const imgs = [
  { uri: 'http://placehold.it/50x50/f00/000?text=R', x: 15, y:  15, sw: 50, sh: 50 },
  { uri: 'http://placehold.it/50x50/ff0/000?text=Y', x: 15, y:  80, sw: 50, sh: 50 },
  { uri: 'http://placehold.it/50x50/0f0/000?text=G', x: 15, y: 145, sw: 50, sh: 50 }
];

imgs.forEach(depict);

#my-canvas { background: #7F7F7F; }

<canvas id="my-canvas" width="80" height="210"></canvas>

Answer 3

我并不肯定，但 imageObj 可能不是您在 imageObj.onload 函数中期望的 imageObj 。而不是做

 context.drawImage(imageObj, sourceX, sourceY,

看看当你这样做时会发生什么

 context.drawImage(this, sourceX, sourceY,

Answer 4

如果您要加载多个图像，建议您首先预加载所有图像。请参阅此处了解更多信息：

http://www.html5canvastutorials.com/tutorials/ html5-canvas-image-loader/

Answer 5

我有类似的问题，
我喜欢 https://developer.mozilla 的解决方案

。 org/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_animations

只需调用 window.requestAnimationFrame(draw);从您的绘图函数中，它将运行无限循环并在图像准备好后立即绘制图像

Answer 6

这是一个解决方案，以及推荐的替代方案；两者都使用 .bind([,][,])

bind 包装预期的函数，并执行使用附加指定参数 (args) 对其进行调用。 bind 的第一个参数将是函数的 this 实例。将其设置为 undefined 将传递原始 this 实例。

匿名函数。

  var settings;

  for(i = 0; i < tiles.length; i++)
  {
      settings = {};
      settings.sourceX = tiles[i][5];
      settings.sourceY = tiles[i][6];
      settings.sourceWidth = tiles[i][9];
      settings.sourceHeight = tiles[i][10];
      settings.destWidth = sourceWidth;
      settings.destHeight = sourceHeight;
      settings.destX = tiles[i][7];
      settings.destY = tiles[i][8];

      settings.imageObj = new Image();
      settings.imageObj.onload = function(args)
      {
         context.drawImage(args.image, args.sourceX, args.sourceY, args.sourceWidth, args.sourceHeight, args.destX, args.destY, args.destWidth, args.destHeight);
      }.bind(undefined, settings);
      settings.imageObj.src = tiles[i][4];
  }

---

不过，我更喜欢不使用匿名函数来处理常见事件；相反，我会声明一个对象来存储处理程序。

这样您就可以在运行时替换处理程序。以如下方式。

声明对象来存储事件处理函数

  var Handlers = { 
      "drawImageHandler" : function drawImageHandler(args)
      {
          context.drawImage(args.image, args.sourceX, args.sourceY, args.sourceWidth, args.sourceHeight, args.destX, args.destY, args.destWidth, args.destHeight);
      }
  };

  function DebugInit() 
  {
      var func = Handlers.drawImageHandler;
      Handlers.drawImageHandler = function(func, args) {
         console.log("%o", args);
         func(args);
      }.bind(undefined, func);
  }


  var settings = {};
  DebugInit(); // when called, encapsulates Handlers.drawImageHandler;

  for(i = 0; i < tiles.length; i++)
  {
      settings = {};
      settings.sourceX = tiles[i][5];
      settings.sourceY = tiles[i][6];
      settings.sourceWidth = tiles[i][9];
      settings.sourceHeight = tiles[i][10];
      settings.destWidth = sourceWidth;
      settings.destHeight = sourceHeight;
      settings.destX = tiles[i][7];
      settings.destY = tiles[i][8];
      settings.imageObj = new Image();
      settings.imageObj.onload = Handlers.drawImageHandler.bind(undefined, settings);      
      settings.imageObj.src = tiles[i][4];
  }

jsFiddle：示例Fiddle< /a>

Answer 7

img[0]=new Image();
img[0].src="imgimg/img"+i+".png";
img[0].onload=function(){
  cntxt.drawImage(this,400,i*100,100,100);
  i++;
  img[i]=new Image(); 
  img[i].src="invimg/img"+i+".png";
  img[i].onload=this.onload;
};

我的js游戏的一部分，希望对你有帮助干杯！