I'am trying to write a puzzle game in canvas,so i need to give each part of puzzle block a background image. but always a error "Uncaught TypeError: Cannot read property 'drawImage' of undefined "
any help will be appreciated!
(function(){
function Block(image, l, t, w, h){
this.image = image;
this.left = l;
this.top = t;
this.width = w;
this.height = h;
}
Block.prototype.draw = function(context){
context.drawImage(this.image, this.left, this.top, this.width, this.height, this.left, this.top, this.width, this.height);
}
window.Block = Block;
})();
var el = document.getElementById("puzzle_area");
var ctx = el.getContext("2d");
var image = new Image();
image.src = "background0.jpg";
image.onload = init;
var width = 100;
var height = width;
function init(){
for(var i = 0; i < 16; i++){
var x = (i % 4) * width;
var y = parseInt(i / 4) * height;
var block = new Block(image, x, y, width, height);
block.draw(ctx);
}
}
Your draw() function requires a context parameter which you're not passing to it when you're calling it from within your Block() function/object. Add a context parameter to that and use it when calling "this.draw()".
I haven't tested it, but here is what I changed your code to:
(function(){
function Block(context, image, l, t, w, h){
this.image = image;
this.left = l;
this.top = t;
this.width = w;
this.height = h;
this.context = context;
this.draw();
}
Block.prototype.draw = function(){
this.context.drawImage(this.image, -this.left, -this.top, this.width, this.height, this.left, this.top);
}
window.Block = Block;
})();
var el = document.getElementById("puzzle_area");
var ctx = el.getContext("2d");
var image = new Image();
image.src = "background0.jpg";
image.onload = init;
var block = null;
var width = 100;
var height = width;
function init(){
for(var i = 0; i < 9; i++){
var x = (i % 400) * width;
var y = parseInt(i / 400) * height;
block = new Block(ctx, image, x, y, width, height);
// block is drawn automatically, no need to draw it again
// block.draw();
}
}
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