[英]draw image from canvas constructor prototype
我正在嘗試預加載一組圖像,並使用canvas構造函數將列表中的第一個圖像繪制到多個畫布上。
看來我什至無法使用原型功能開始加載圖像。 控制台日志說this.setImages不是函數。 我只是從js開始,因此這可能是一個非常簡單的錯誤。
我在代碼中留下了一些注釋,希望它能使它變得清楚一點。
還有其他方法可以實現我要的功能,但就我而言,我必須使用構造函數。
var sources = [
'http://i.telegraph.co.uk/multimedia/archive/02830/cat_2830677b.jpg',
'http://r.ddmcdn.com/w_622/u_0/gif/05-kitten-cuteness-1.jpg',
'http://simplycatbreeds.org/images/Kitten.jpg'];
var images = [];
var canvas1 = new canvas('canvas1');
var canvas2 = new canvas('canvas2');
// load images using callback function
setImages(sources, function(images){
window.alert("Done loading... Start!");
this.draw();
});
// canvases constructor
function canvas(canvasId) {
this.canvas = document.getElementById(canvasId);
this.context = this.canvas.getContext('2d');
this.canvas.style.width = '100%';
this.canvas.style.height = '100%';
this.canvasId = canvasId;
this.setImages();
};
// preloading images
canvas.prototype.setImages = function(sources, callback){
var cnt = 0;
function imagesLoaded(){
cnt++;
if (cnt >= sources.length){
// passing the objet containing images to load as parameteres
callback(images);
}
}
for (var i=0; i<sources.length; i++) {
images[i] = new Image();
images[i].src = sources[i];
images[i].onload = function(){
imagesLoaded();
}
}
};
canvas.prototype.draw = function() {
// some code to manipulate image to be added here...
this.context.drawImage(images[1], 0, 0);
};
這是FIDDLE的例子
嘗試像這樣在畫布函數內部移動setImages函數:
function canvas(canvasId)
{
this.setImages = function(...){ };
...
this.setImages();
}
在第13行中,應該在畫布對象上調用setImages:canvas1.setImages();。
我已經修復了一些問題。
首先,我將創建兩個對象的代碼移到了JS的末尾。 原因是在嘗試訪問原型功能之前必須先加載它們。 我建議使用諸如window.onload
類的事件偵聽器,以防止代碼在加載所有內容之前啟動。
其次,我更改了setImage
以便在canvas
對象上調用它。
var sources = [...];
var images = [];
// load images using callback function
// canvases constructor
function canvas(canvasId) {
this.canvas = document.getElementById(canvasId);
this.context = this.canvas.getContext('2d');
this.canvas.style.width = '100%';
this.canvas.style.height = '100%';
this.canvasId = canvasId;
//I removed this since it does not have the right params
//this.setImages();
};
// preloading images
canvas.prototype.setImages = function(sources, callback){
var cnt = 0;
var obj = this;
function imagesLoaded(){
cnt++;
if (cnt >= sources.length){
// passing the objet containing images to load as parameteres
callback(images, obj);
}
}
for (var i=0; i<sources.length; i++) {
images[i] = new Image();
images[i].src = sources[i];
images[i].onload = function(){
imagesLoaded();
}
}
};
canvas.prototype.draw = function() {
// some code to manipulate image to be added here...
this.context.drawImage(images[1], 0, 0);
};
var canvas1 = new canvas('canvas1');
canvas1.setImages(sources, function(images){
window.alert("Done loading... Start!");
this.draw();
});
var canvas2 = new canvas('canvas2');
canvas2.setImages(sources, function(images, obj){
window.alert("Done loading... Start!");
obj.draw();
});
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