Question

I have started learning Canvas in HTML5 and I have a question.

I want create a movable pattern with repeat. (Something like background-position and background-repeat in CSS.)

How can I do this?

I need this to create an animated background for my project.

Answer 1

Theres a few ways to achieve this the you could use putImageData but you would suffer some performance loss, the best method is to use drawImage. Also note the 2nd method has the code to make it go either from left to right, or right to left.

http://www.somethinghitme.com/projects/bgscroll/scrolldrawimage.html

var ctx = document.getElementById("canvas").getContext("2d"),
    canvasTemp = document.createElement("canvas"),
    scrollImg = new Image(),
    tempContext = canvasTemp.getContext("2d"),
    imgWidth = 0,
    imgHeight =0,
    imageData = {},
    canvasWidth = 600,
    canvasHeight = 240,
    scrollVal = 0,
    speed =2;

    scrollImg.src = "citybg.png";
    scrollImg.onload = loadImage;

function loadImage(){
    imgWidth = scrollImg.width,
    imgHeight = scrollImg.height;
    canvasTemp.width = imgWidth;
    canvasTemp.height =  imgHeight;    
    render();                
}

function render(){
    ctx.clearRect(0,0,canvasWidth,canvasHeight);

    if(scrollVal >= canvasWidth){
        scrollVal = 0;
    }

    scrollVal+=speed;                   
    ctx.drawImage(scrollImg,canvasWidth-scrollVal,0,scrollVal,imgHeight, 0, 0, scrollVal,imgHeight);
    ctx.drawImage(scrollImg,scrollVal,0,imgWidth, imgHeight);

     // To go the other way instead
     ctx.drawImage(scrollImg,-scrollVal,0,imgWidth, imgHeight);
     ctx.drawImage(scrollImg,canvasWidth-scrollVal,0,imgWidth, imgHeight);

    setTimeout(function(){render();},10);
}