Creating Watermarked Images in PhoneGap
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Join For FreeA reader asked me if it was possible to watermark images (like those taken with a camera) in PhoneGap. This is rather trivial using Canvas (hey, it does have a use!) so I whipped up the following example to demonstrate it in action.
First - let's look at the code. It's short enough to show all at once:
<!DOCTYPE html> <html> <head> <script src="cordova-1.7.0.js"></script> <script src="jquery.min.js"></script> <script> var watermark; var canvasDom; var canvas; function init() { document.addEventListener("deviceready", startUp, false); } function startUp() { canvasDom = $("#myCanvas")[0]; canvas = canvasDom.getContext("2d"); //Create a watermark image object watermark = new Image(); watermark.src = "rk.png"; watermark.onload = function(e) { //you can only take pictures once this is loaded... $("#takePictureButton").removeAttr("disabled"); } $("#takePictureButton").on("touchstart", function(e) { navigator.camera.getPicture(camSuccess, camError, {quality: 75, targetWidth: 400, targetHeight: 400, destinationType: Camera.DestinationType.FILE_URI}); }); function camError(e) { console.log("Camera Error"); console.log(JSON.stringify(e)); } function camSuccess(picuri) { console.log("Camera Success"); var img = new Image(); img.src=picuri; img.onload = function(e) { canvas.drawImage(img, 0, 0); canvas.drawImage(watermark, canvasDom.width-watermark.width, canvasDom.height - watermark.height); } } } </script> <style> #myCanvas { width: 400px; height: 400px; } </style> </head> <body onload="init()"> <h1>Watermark Test</h1> <button id="takePictureButton" disabled>Take a Picture</button> <p/> <canvas id="myCanvas"></canvas> </body> </html>
The UI for the application is just a header and a button. I've got the button initially disabled as I need to ensure some resources load before you start taking pictures.
Looking at the JavaScript code, you can see that I've created a canvas instance from the DOM and have created a watermark image. When it loads, I'm ready to watermark so I enable the button.
The button's touchstart event ties in to the PhoneGap Camera API to trigger the device to create a new picture. I could allow for gallery photos as well or make use of images from the web.
Once you take a picture, it's a trivial matter then to load it into an image object and copy it onto the canvas. Note that I place the watermark in the lower right hand corner of the image. That's where most watermarks seem to go so I did the same.
Here's a quick example. Forgive the horrible quality of the Xoom camera.
You can do anything you want with the image now, including getting the bits and uploading it to a server.
Published at DZone with permission of Raymond Camden, DZone MVB. See the original article here.
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