There are hundreds of tutorials, how one can crop an image by drawImage() on a canvas.
context.drawImage(imageObj, sourceX, sourceY, sourceWidth, sourceHeight, destX, destY, destWidth, destHeight);
However, I have a canvas that fills the user's browser. By exporting the canvas as an image I would like to export only an area of 640px*480px from (0|0).
Problem: How can I tell javascript to use only 640*480 of the canvas for the toDataURL()?
Here is what I have so far:
$("#submitGraphic").click( function(){
var canvas = document.getElementsByTagName("canvas");
// canvas context
var context = canvas[0].getContext("2d");
// get the current ImageData for the canvas
var data = context.getImageData(0, 0, canvas[0].width, canvas[0].height);
// store the current globalCompositeOperation
var compositeOperation = context.globalCompositeOperation;
// set to draw behind current content
context.globalCompositeOperation = "destination-over";
//set background color
context.fillStyle = "#FFFFFF";
// draw background/rectangle on entire canvas
context.fillRect(0,0,canvas[0].width,canvas[0].height);
// not working, seems to clear the canvas? browser hangs?
// seems that I can click a white image in the background
/*canvas[0].width = 640;
canvas[0].height = 480;*/
// not working either
/*canvas[0].style.width = '640px';
canvas[0].style.height = '480px';*/
// not working at all
/*context.canvas.width = 640;
context.canvas.height = 480;*/
// write on screen
var img = canvas[0].toDataURL("image/png");
document.write('<a href="'+img+'"><img src="'+img+'"/></a>');
})
PS: I do not want to resize or scale, just clipping/cropping to the fixed window. Here I read that you only specifiy canvas.width and canvas.height - but this clears the canvas.
The best way is to just create a temporary canvas to draw onto from the current canvas. The user will never see this temp canvas. Then you just need use toDataUrl()
on the temp canvas.
$("#submitGraphic").click( function(){
var canvas = document.getElementsByTagName("canvas");
// canvas context
var context = canvas[0].getContext("2d");
// get the current ImageData for the canvas
var data = context.getImageData(0, 0, canvas[0].width, canvas[0].height);
// store the current globalCompositeOperation
var compositeOperation = context.globalCompositeOperation;
// set to draw behind current content
context.globalCompositeOperation = "destination-over";
//set background color
context.fillStyle = "#FFFFFF";
// draw background/rectangle on entire canvas
context.fillRect(0,0,canvas[0].width,canvas[0].height);
var tempCanvas = document.createElement("canvas"),
tCtx = tempCanvas.getContext("2d");
tempCanvas.width = 640;
tempCanvas.height = 480;
tCtx.drawImage(canvas[0],0,0);
// write on screen
var img = tempCanvas.toDataURL("image/png");
document.write('<a href="'+img+'"><img src="'+img+'"/></a>');
})