[英]Why is my canvas only loading the images in the top left corner?
我正在嘗試制作一個可以制作視頻游戲地圖的程序。 之前它工作得非常好,但是我添加了一個變量pixelWideAndTall來自動設置畫布的寬度和高度,現在它只會將圖像加載到左上角。 我只想知道為什么會這樣以及如何解決。 如果需要查看它,則必須將代碼復制並粘貼到使用的任何文本編輯器中。 我會發布圖片,但是我的聲譽不夠高。 謝謝!
<html>
<head>
<title></title>
<script>
window.onload = function () {
var canvas = document.getElementById('paper');
var c = canvas.getContext('2d');
var posX=0; //All of my variables
var posY=0;
var pixelWideAndTall = prompt('How wide and tall do you want each picture to be? Make sure it\'s a number, please!');
while(isNaN(pixelWideAndTall)){
pixelWideAndTall = prompt('Alright, put in a number this time.');
}
var map = [
[0,0,1,0,0], //Map
[0,0,1,0,0],
[1,1,1,1,1],
[0,0,1,0,0],
[0,0,1,0,0]];
canvas.height = map.length * pixelWideAndTall;
canvas.width = map[0].length * pixelWideAndTall;
//Now for the pictures!
var grass = new Image();
grass.src='https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-ash3/v/t1.0-9/10252096_483877768405708_6915128458002047622_n.jpg?oh=0dd45ac8392b31dd89da67f2b74e0eef&oe=53ABDB2A&__gda__=1404253465_7ee03498efb21d7759862a3268769775';
var sand = new Image();
sand.src='https://scontent-b-sea.xx.fbcdn.net/hphotos-prn2/t1.0-9/10169458_483877771739041_423139715070437533_n.jpg';
var logA = new Image();
logA.src='https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-frc1/t1.0-9/10014648_483877575072394_6204441713213423736_n.jpg';
var logB = new Image();
logB.src='https://scontent-a-sea.xx.fbcdn.net/hphotos-frc1/t1.0-9/10247323_483877578405727_3664131849980667819_n.jpg';
for(var i=0;i<map.length;i++){
for(var j=0;j<map[i].length;j++){
switch(map[i][j]){
case 0:
c.drawImage(grass,posX,posY,pixelWideAndTall,pixelWideAndTall);
break;
case 1:
c.drawImage(sand,posX,posY,pixelWideAndTall,pixelWideAndTall);
/*Loops through every spot of the array. Based on what's
in that particular index, it draws a certain picture. */
break;
case 2:
c.drawImage(logA,posX,posY,pixelWideAndTall,pixelWideAndTall);
break;
case 3:
c.drawImage(logB,posX,posY,pixelWideAndTall,pixelWideAndTall);
break;
default:
alert('You must have put in an input that isn\'t supported yet. Please fix!');
break;
}
posX+=pixelWideAndTall;
}
posX=0;
posY+=pixelWideAndTall;
}
}
</script>
<style>
#paper{
border:3px solid black;
}
p{
font-size:6px;
}
</style>
</head>
<body> <!-- Just in case... -->
<canvas id='paper' height = 0 width = 0>Your browser does not support the HTML5 Canvas element. Either try a different browser, or just give it up.</canvas>
<p>You <strong><em>may</em></strong> need to refresh a few times for the image to load. Thank you!</p>
</body>
</html>
這是因為從提示返回時, pixelWideAndTall
變量是一個字符串。
使用乘法時,它將轉換為數字,這就是為什么它可以與以下行一起使用的原因:
canvas.height = map.length * pixelWideAndTall;
但不是在添加時 -因此發生的是,該值被串聯為字符串,而不是在循環中的posX等加號運算符處。
要解決此問題,只需立即將其強制為一個數字即可:
var pixelWideAndTall = prompt('...');
while(isNaN(pixelWideAndTall)){
pixelWideAndTall = prompt('Alright, put in a number this time.');
}
pixelWideAndTall *= 1; // this will force it to a number
可選:
pixelWideAndTall = parseInt(pixelWideAndTall, 10);
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