//Negatyw
//(c) 2011 by Tomasz Lubinski
//www.algorytm.org

/* Source of the image */
var imgSrc;

/* make canvas negative */
function nagatyw()
{
	var canvas = document.getElementById("canvas");
	var ctx = canvas.getContext("2d");

	// read the width and height of the canvas
	var width = canvas.width;
	var height = canvas.height;

	// create a new pixel array
	var imageData;
	try 
	{
    		imageData = ctx.getImageData(0, 0, width, height);
  	} catch(e) 
  	{
  		netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
  		imageData = ctx.getImageData(0, 0, width, height);
  	}
	
	// make nagative
	for (var i=0; i<height; i++)
	{
		for (var j=0; j<width; j++)
		{
			index = (i*width+j)*4;
			// invert pixel
			imageData.data[index+3] = 255;
			imageData.data[index+0] = 255-imageData.data[index+0];
			imageData.data[index+1] = 255-imageData.data[index+1];
			imageData.data[index+2] = 255-imageData.data[index+2];
		}
	}
	
	// copy the image data back onto the canvas
	ctx.putImageData(imageData, 0, 0);	
}

/* load image pointed by param_file to canvas */
function loadImage() 
{
	var canvas = document.getElementById("canvas");
	var ctx = canvas.getContext("2d");
	
	// add file:// if user specified local path
	if (imgSrc.indexOf("//") == -1 && imgSrc.indexOf(".") != 0) 
	{
		imgSrc = "file:///" + imgSrc;
	}
	
	// load file into canvas
	var img = new Image();
  	img.src = imgSrc;
  	img.onload = function(){
		var width = img.width;
		var height = img.height;
 		canvas.width = width;
  		canvas.height = height;
  		ctx.drawImage(img,0,0);
		// replace transparent with white
		var imageData;
		try 
		{
    			imageData = ctx.getImageData(0, 0, width, height);
  		} catch(e) 
  		{
  			netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
  			imageData = ctx.getImageData(0, 0, width, height);
  		}
		for (var i=0; i<height; i++)
		{
			for (var j=0; j<width; j++)
			{
				index = (i*width+j)*4;
				if (imageData.data[index+3] == 0)
				{
					imageData.data[index+3] = 255;
					imageData.data[index+0] = 255;
					imageData.data[index+1] = 255;
					imageData.data[index+2] = 255;
				}
			}
		}
		ctx.putImageData(imageData, 0, 0);
  	}
}