移动画布图案的起始位置

Question

我有一个代码:

function draw(ctx) {
  // create new image object to use as pattern
  var img = new Image();
  img.onload = function(){
    // create pattern
    var ptrn = ctx.createPattern(img,'repeat');
    ctx.fillStyle = ptrn;
    ctx.fillRect(0,0,150,150);
  }
  img.src = 'images/wallpaper.png?' + new Date().getTime();
}

如何移动图案图像的起始位置？

Answer 1

在回答接受的答案时:我会使用save()&restore()来避免潜在的问题,而不是撤消偏移量:

ctx.save();
ctx.translate(offset_x, offset_y);
ctx.fillRect(-offset_x, -offset_y, fill_x, fill_y);
ctx.restore();

Answer 2

您可以通过翻译画布,在其上绘图,然后将其翻译回您开始的位置来实现此目的:

function draw(ctx) {
    // create new image object to use as pattern
    var img = new Image();
    img.onload = function(){
        // create pattern
        var ptrn = ctx.createPattern(img,'repeat');
        ctx.fillStyle = ptrn;

        // offset vars
        var offset_x = 60;
        var offset_y = 75;
        var fill_x = 500; // could be canvas.width
        var fill_y = 500; // could be canvas.height

        // offset
        ctx.translate(offset_x, offset_y);

        // draw
        ctx.fillRect(-offset_x, -offset_y, fill_x, fill_y);

        // undo offset
        ctx.translate(-offset_x, -offset_y);
    }
    img.src = 'images/wallpaper.png?' + new Date().getTime();
}