HTML5 CANVAS draw image

Question

Here is my question

I kind of not understand what is the sx and sy is for in below function

context.drawImage(Image, sx, sy, sw, sh, dx, dy, dw, dh);

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Answer 1

(sx, sy) is the top-left corner of the source rectangle (within the source image) which are going to draw to the destination. Take a look at the diagram below:

[Reference]

sx=0,sy=0 is different from sx=300,sy=300 because they refer to different source rectangles.

Answer 2

var img = new Image();
img.onload = function init_sketch() {
img.src = 'http://cssdeck.com/uploads/media/items/3/3yiC6Yq.jpg';
context.drawImage(img, 0, 0);
}