[英]Scrolling Pictures with javascript
我已经编写了一个JavaScript,该Javascript应该使用画布在屏幕上滚动图片。 我无法使它正常工作,将不胜感激。 我能够使用一张图片而不使用Array来使它工作,但是我希望能够使用Array并一张一张又一张地加载图片,并且它们之间的空间很小。
var img = new Image[];
img[0] = new Image;
img[0].src = 'Images/Juniors.jpg';
img[1] = new Image;
img[1].src = 'Images/minis.jpg';
img[2] = new Image;
img[2].src = 'Images/senior.jpg';
var CanvasXSize = 1040;
var CanvasYSize = 240;
var speed = 40; //lower is faster
var scale = 1.05;
var y = -4.5; //vertical offset
var dx = 0.75;
var imgW;
var imgH;
var x = 0;
var clearX;
var clearY;
var ctx;
img.onload = function() {
imgW = img.width*scale;
imgH = img.height*scale;
if (imgW > CanvasXSize) { x = CanvasXSize-imgW; } // image larger than canvas
if (imgW > CanvasXSize) { clearX = imgW; } // image larger than canvas
else { clearX = CanvasXSize; }
if (imgH > CanvasYSize) { clearY = imgH; } // image larger than canvas
else { clearY = CanvasYSize; }
ctx = document.getElementById('canvas').getContext('2d'); //Get Canvas Element
}
function draw() {
//Clear Canvas
ctx.clearRect(0,0,clearX,clearY);
//If image is <= Canvas Size
if (imgW <= CanvasXSize) {
//reset, start from beginning
if (x > (CanvasXSize)) { x = 0; }
//draw aditional image
if (x > (CanvasXSize-imgW)) {
ctx.drawImage(img, x-CanvasXSize+1, y, imgW, imgH);
}
}
//If image is > Canvas Size
else {
//reset, start from beginning
if (x > (CanvasXSize)) { x = CanvasXSize-imgW; }
//draw aditional image
if (x > (CanvasXSize-imgW)) { ctx.drawImage(img[0],x-imgW+1,y,imgW,imgH); }
}
for(i = 0; i < img.length; i++) {
ctx.drawImage(img[i],x,y,imgW,imgH);
//amount to move
x += dx;
}
}
要在需要时加载多个图像,应使用图像预加载器代码:
var imgs=[];
var imagesOK=0;
var imageURLs=[];
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house1.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house2.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house3.jpg");
loadAllImages();
function loadAllImages(){
for (var i = 0; i < imageURLs.length; i++) {
// put each image in the imgs array
var img = new Image();
imgs.push(img);
// after each image has been loaded, execute this function
img.onload = function(){
// add 1 to imagesOK
imagesOK++;
// if imagesOK equals the # of images in imgs
// we have successfully preloaded all images
// into imgs[]
if (imagesOK>=imageURLs.length ) {
// all loaded--start drawing the images
drawImages();
}
}; // end onload
img.src = imageURLs[i];
} // end for
}
此时,图像均已加载,因此请绘制图像
您可以使用context.translate和context.rotate倾斜图像。
您要做的是平移(移动)到要旋转的图像的中心。 然后从该中心点旋转。 这样,图像将绕其中心旋转。 旋转功能采用弧度角,因此您可以将度数转换为弧度,如下所示:30度= 30 * Math.PI / 180弧度
ctx.translate( left+width/2, topp+height/2 )
ctx.rotate( degrees*Math.PI/180 );
然后,将图像偏移其中心点(请记住您围绕该中心点旋转)
ctx.drawImage(img,0,0,img.width,img.height,-width/2,-height/2,width,height);
花费很多精力,所以这里有示例代码和小提琴: http : //jsfiddle.net/m1erickson/t49kU/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var imgs=[];
var imagesOK=0;
var imageURLs=[];
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house1.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house2.jpg");
imageURLs.push("https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house3.jpg");
loadAllImages();
function loadAllImages(){
for (var i = 0; i < imageURLs.length; i++) {
var img = new Image();
imgs.push(img);
img.onload = function(){
imagesOK++;
if (imagesOK>=imageURLs.length ) {
drawImages();
}
}; // end onload
img.src = imageURLs[i];
} // end for
}
ctx.lineWidth=2;
var left=25;
var topp=30;
var width=100;
var height=100;
var rotations=[ -10, 0, 10 ];
function drawImages(){
for(var i=0;i<imgs.length;i++){
var img=imgs[i];
ctx.save()
ctx.beginPath();
ctx.translate( left+width/2, topp+height/2 )
ctx.rotate(rotations[i]*Math.PI/180);
ctx.drawImage(img,0,0,img.width,img.height,-width/2,-height/2,width,height);
ctx.rect(-width/2,-height/2,width,height);
ctx.stroke();
ctx.restore();
left+=125;
}
}
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=400 height=200></canvas>
</body>
</html>
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