Solved

Call java putImageData from an HTML tag

Posted on 2012-03-25
4
465 Views
Last Modified: 2012-03-25
I have HTML canvas javascript code that uses getImageData to save the entire canvas (see code below). I have created a function with putImageData in it so I can call the function from an HTML tag. I made the variables context and ImageData global but I can't get the putImageData to work.  What am I doing wrong? TIA
<a href="#" onclick="clearCanvas()"><img src="clearall.png" width="224" height="56" alt="Clear All" border="0">

var context, ImageData;

var img=new Image();
img.onload = function()
{
   context.drawImage(img,0,0);
   imageData = context.getImageData(0, 0, 700, 643);
   pixels = imageData.data;
};
img.src="PainDiagram.png";

function clearCanvas()
{
   context.putImageData(imageData, 0, 0);
}

Open in new window

0
Comment
Question by:thenelson
  • 2
  • 2
4 Comments
 
LVL 38

Expert Comment

by:Tom Beck
ID: 37762891
Context is undefined. It should be the context of the canvas you intend to draw the image upon.

context = document.getElementById('canvasId').getContext("2d");

Other than that, your clearCanvas function should work as is.
0
 
LVL 39

Author Comment

by:thenelson
ID: 37763281
I do have context defined:
    // Get the 2D canvas context.
    context = canvas.getContext('2d');
    if (!context) {
      alert('Error: failed to getContext!');
      return;
    }

Open in new window


Here is the entire js file as it is now:
/* © 2009 ROBO Design
 * http://www.robodesign.ro
 */

// Keep everything in anonymous function, called on window load.
if(window.addEventListener) {
window.addEventListener('load', function () {
  var canvas, context, tool;
  var lastX, lastY, prevX, prevY, segCount, reptSeg;


  function init () {
    // Find the canvas element.
    canvas = document.getElementById('imageView');
    if (!canvas) {
      alert('Error: I cannot find the canvas element!');
      return;
    }

    if (!canvas.getContext) {
      alert('Error: no canvas.getContext!');
      return;
    }

    // Get the 2D canvas context.
    context = canvas.getContext('2d');
    if (!context) {
      alert('Error: failed to getContext!');
      return;
    }
	
	var img=new Image();
	img.onload = function(){
	context.drawImage(img,0,0);
	var imageData = context.getImageData(0, 0, 700, 643);
    pixels = imageData.data;
	};
	img.src="PainDiagram.png";

    // Pencil tool instance.
    tool = new tool_pencil();

    // Attach the mousedown, mousemove and mouseup event listeners.
    canvas.addEventListener('mousedown', ev_canvas, false);
    canvas.addEventListener('mousemove', ev_canvas, false);
    canvas.addEventListener('mouseup',   ev_canvas, false);
  }

  // This painting tool works like a drawing pencil which tracks the mouse 
  // movements.
  function tool_pencil () {
    var tool = this;
    this.started = false;

    // This is called when you start holding down the mouse button.
    // This starts the pencil drawing.
    this.mousedown = function (ev) {
			context.lineCap = "round";
			context.strokeStyle = color_value;
			lastX = ev._x;
			lastY = ev._y;
			prevX = ev._x;
			prevY = ev._y;
			segCount = 0;
			if (color_value == "#FF7F50")	 //referred pain
			{
				context.lineWidth = 2;
				reptSeg = 7;
			}
			else
			{
				context.lineWidth = 10;
				reptSeg = 1;
			}
	
	    context.beginPath();
//        context.moveTo(ev._x, ev._y);
        tool.started = true;
    };

    // This function is called every time you move the mouse. Obviously, it only 
    // draws if the tool.started state is set to true (when you are holding down 
    // the mouse button).
    this.mousemove = function (ev) {
		if (tool.started) {
			if(!segCount)
			{
				prevX = lastX;
				prevY = lastY;
				lastX = ev._x;
				lastY = ev._y;
				segCount = reptSeg;
				context.lineTo(ev._x, ev._y);
				context.stroke();
			}
			segCount--;
		}
    };

    // This is called when you release the mouse button.
    this.mouseup = function (ev) {
		if (tool.started) 
		{
			if (color_value == "#FF7F50")
			{
				var angle = Math.atan2(lastY-prevY,lastX-prevX);
		  		context.beginPath();
				context.moveTo(lastX+15*Math.cos(angle),lastY+15*Math.sin(angle));
				context.lineTo(lastX-7*Math.cos(angle-Math.PI/4),lastY-7*Math.sin(angle-Math.PI/4));
		  		context.lineTo(lastX-7*Math.cos(angle+Math.PI/4),lastY-7*Math.sin(angle+Math.PI/4)); 
				context.closePath();
				context . fillStyle  = color_value;
				context.fill();
			}
			tool.started = false;
			tool.mousemove(ev);
			var imageData2 = context.getImageData(0, 0, 700, 643);
			   var newPixels = imageData2.data;
			   for (var i = 0, il = pixels.length; i < il; i += 4) 
			{
			   	if((pixels[i] == 255 && pixels[i+1] == 204 && pixels[i+2] == 153) 
				|| (newPixels[i] > 235 && newPixels[i+1] < 150 && newPixels[i+2] > 75 && newPixels[i+2] < 110))
				{
				}
				else
			 		{	
			           newPixels[i] = pixels[i];
			           newPixels[i+1] = pixels[i+1];
			           newPixels[i+2] = pixels[i+2];
			   	}
			   }
			   context.putImageData(imageData2, 0, 0);
			   //document.form.output.value = document.form.output.value + " x= " + ev._x + ",  y= " + ev._y + "\nLX= " + lastX + ", LY= " + lastY +  "\npX= " + prevX + ", pY= " + prevY + "\nsegCount= " + segCount + "\n\n";
		}
    };
  }

  // The general-purpose event handler. This function just determines the mouse 
  // position relative to the canvas element.
  
 
  function ev_canvas (ev) {
    if (ev.offsetX || ev.offsetX == 0) { // Opera and WebKit
      ev._x = ev.offsetX;
      ev._y = ev.offsetY;
    }  
    else if (ev.layerX || ev.layerX == 0) { // Firefox
      ev._x = ev.layerX;
      ev._y = ev.layerY;
    } 

    // Call the event handler of the tool.
    var func = tool[ev.type];
    if (func) {
      func(ev);
    }
  }

  init();
  

}, false); }


// vim:set spell spl=en fo=wan1croql tw=80 ts=2 sw=2 sts=2 sta et ai cin fenc=utf-8 ff=unix:

Open in new window

0
 
LVL 38

Accepted Solution

by:
Tom Beck earned 500 total points
ID: 37763394
Works fine. As long as you are not re-declaring imageData as in line 35:

var imageData = context.getImageData(0, 0, 700, 643);

Or context as in line 8:

var canvas, context, tool;

And your two variables, context and imageData, are declared first outside of all functions.
0
 
LVL 39

Author Closing Comment

by:thenelson
ID: 37763755
I got it working.  I didn't make the declarations of imageData and context truly global before - they were in a function.

Thanks again!
0

Featured Post

Highfive + Dolby Voice = No More Audio Complaints!

Poor audio quality is one of the top reasons people don’t use video conferencing. Get the crispest, clearest audio powered by Dolby Voice in every meeting. Highfive and Dolby Voice deliver the best video conferencing and audio experience for every meeting and every room.

Join & Write a Comment

Suggested Solutions

Nothing in an HTTP request can be trusted, including HTTP headers and form data.  A form token is a tool that can be used to guard against request forgeries (CSRF).  This article shows an improved approach to form tokens, making it more difficult to…
This article demonstrates how to create a simple responsive confirmation dialog with Ok and Cancel buttons using HTML, CSS, jQuery and Promises
The viewer will learn how to dynamically set the form action using jQuery.
The viewer will learn how to create and use a small PHP class to apply a watermark to an image. This video shows the viewer the setup for the PHP watermark as well as important coding language. Continue to Part 2 to learn the core code used in creat…

708 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

17 Experts available now in Live!

Get 1:1 Help Now