javascript - 如何从数组中的图像源创建 Canvas 图像？

Question

我想从来自 ajax 请求的数组中的多个图像创建 Canvas 图像；为此，我尝试运行循环，但 drawImage 不适用于循环。

然后我尝试一个函数，并在循环中调用该函数，但发生同样的事情 drawImage 不适用于此

下面我提到了所有代码，其中一个包含循环函数，一个包含当前正在工作的 drawImage 中的静态信息。

如果你们中有人能指导我如何解决这个问题，我将非常感激。

工作正常的静态drawImage代码

function loadImages(sources, callback, imagesrc) {
        var images = {};
        var loadedImages = 0;
        var numImages = 0;

        for(var src in sources) {
          numImages++;
        }

        for(var src in sources) {
          images[src] = new Image();
          images[src].onload = function() {
            if(++loadedImages >= numImages) {
              callback(images);
            }
          };
          images[src].src = sources[src];
        }


 }

      var canvas = document.getElementById('product-image');

      canvas.height = (jQuery(window).height()) -120;
      canvas.width = canvas.height * 0.75;
      var heightscreen = (jQuery(window).height()) -120;
      var canvasheight = heightscreen;
      var canvaswidth = canvas.height * 0.75;
      canvaswidthdiv4 = 0;
      var widthNeeded = canvasheight * 0.75;

      var context = canvas.getContext('2d');

// THIS IS A DUMMY ARRAY SAME AS COME IN AJAX RESPONSE  
        var sources = 
        {        
        Slim_Fit: "http://localhost/plugindev/wp-content/uploads/2015/08/slimFit.png",
        Inside_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/maincolar.png",
        Outside_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/outer_collar1.png",
        Main_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/inner_collar11.png"
        };



      loadImages(sources, function(images) 
      {

        context.drawImage(images.Slim_Fit, canvaswidthdiv4, 55, widthNeeded, canvasheight);  
        context.drawImage(images.Inside_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);
        context.drawImage(images.Outside_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);
        context.drawImage(images.Main_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);

      });

以下是我用于功能但不起作用的修改

 loadImages(sources, function(images) 
  {
jQuery.each( sources, function( key, value ) {

 DrawImage(key, images );

  });

  });

function DrawImage(keyname,images){

context.drawImage(images.keyname, canvaswidthdiv4, 55, widthNeeded, canvasheight);      
        }

下面是我使用循环绘制时的修改，但效果不佳

 loadImages(sources, function(images) 
  {
jQuery.each( sources, function( key, value ) {

 context.drawImage(images.key, canvaswidthdiv4, 55, widthNeeded, canvasheight);

  });

  });

请帮忙!

Answer 1

注意，问题中的 js 似乎在 .drawImage 的第二个、第三个、第四个参数处将先前绘制的图像上的每个图像绘制到 canvas 上加载图像？

loadImages(sources, function(images) 
      {    
        context.drawImage(images.Slim_Fit, canvaswidthdiv4, 55, widthNeeded, canvasheight);  
        context.drawImage(images.Inside_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);
        context.drawImage(images.Outside_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);
        context.drawImage(images.Main_Colar, canvaswidthdiv4, 55, widthNeeded, canvasheight);

      });

另请注意来源位于

// THIS IS A DUMMY ARRAY SAME AS COME IN AJAX RESPONSE  
        var sources = 
        {        
        Slim_Fit: "http://localhost/plugindev/wp-content/uploads/2015/08/slimFit.png",
        Inside_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/maincolar.png",
        Outside_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/outer_collar1.png",
        Main_Colar: "http://localhost/plugindev/wp-content/uploads/2015/08/inner_collar11.png"
        };

是对象，不是数组

<小时/>

js 可以缩短为单个 .forEach() 循环；在 .forEach 回调中调用 .drawImage 时根据需要调整 canvas 上的位置

var canvas = document.getElementById("product-image");
/*
canvas.height = (jQuery(window).height()) - 120;
canvas.width = canvas.height * 0.75;
var heightscreen = (jQuery(window).height()) - 120;
var canvasheight = heightscreen;
var canvaswidth = canvas.height * 0.75;
canvaswidthdiv4 = 0;
var widthNeeded = canvasheight * 0.75;
*/

var context = canvas.getContext('2d');

var images = ["http://lorempixel.com/50/50/cats"
              , "http://lorempixel.com/50/50/nature"
              , "http://lorempixel.com/50/50/animals"
              , "http://lorempixel.com/50/50/sports"
];

images.forEach(function(src, index) {
  var img = new Image;
  img.onload = function() {
    context.drawImage(this, index * this.width, index * this.width)
  }
  img.src = src
})

<canvas id="product-image" width="400px" height="400px"></canvas>