High resolution PDFs from Flex

I was recently working on a mechanism to save some panels (similar to some Dashboard graphics from the Klok 2 dashboard view) created in a Flex application to the user's harddrive by converting them to PDF. The obvious choice for PDF creation is AlivePDF. However, the quality of the resulting PDF was...well terrible. The problem was that instead of trying to recreate every last bit of my app in the PDF, I was just passing a reference to each panel into the pdf.addImage method like so:

pdf.addImage(myPanel)

What this actually does is take a low resolution screenshot (72 DPI) of the component and add it as an image to the pdf. So when you print the pdf, the quality is pretty bad. After some digging I found this post which seemed to be exactly what I was looking for. I thought that simply doing this would do the trick:

var image:ImageSnapshot = ImageSnapshot.captureImage(myPanel, 300, new PNGEncoder());

The problem is caused by the fact that Alive PDF doesn't support transparent PNGs which is what is returned when using the PNGEncoder class which is part of Flex.

A little more digging (several hours worth actually) turned up this post which again sounded like my solution. Applying the code fix from that got me almost there. I created my own NonTransparentPNGEncoder which was basically a copy of the built in PNGEncoder with this new version of internalEncode() method:

private function internalEncode(source:Object, width:int, height:int,

transparent:Boolean = false):ByteArray

{

// The source is either a BitmapData or a ByteArray.

var sourceBitmapData:BitmapData = source as BitmapData;

var sourceByteArray:ByteArray = source as ByteArray;

if (sourceByteArray)

sourceByteArray.position = 0;

// Create output byte array

var png:ByteArray = new ByteArray();

// Write PNG signature

png.writeUnsignedInt(0x89504E47);

png.writeUnsignedInt(0x0D0A1A0A);

// Build IHDR chunk

var IHDR:ByteArray = new ByteArray();

IHDR.writeInt(width);

IHDR.writeInt(height);

IHDR.writeByte(8); // bit depth per channel

IHDR.writeByte(2); // color type: RGBA

IHDR.writeByte(0); // compression method

IHDR.writeByte(0); // filter method

IHDR.writeByte(0); // interlace method

writeChunk(png, 0x49484452, IHDR);

// Build IDAT chunk

var IDAT:ByteArray = new ByteArray();

for (var y:int = 0; y <>

{

IDAT.writeByte(0); // no filter

var x:int;

var pixel:uint;

for (var j:int = 0; j <>

{

pixel = sourceBitmapData.getPixel(j, y);

IDAT.writeByte(pixel >> 16 & 0xFF);

IDAT.writeByte(pixel >> 8 & 0xFF);

IDAT.writeByte(pixel & 0xFF);

}

}

IDAT.compress();

writeChunk(png, 0x49444154, IDAT);

// Build IEND chunk

writeChunk(png, 0x49454E44, null);

// return PNG

png.position = 0;

return png;

}

One final change and I finally had it working:

pdf.addPage();

var image:ImageSnapshot = ImageSnapshot.captureImage(page, 300, new NonTransparentPNGEncoder());

var resize:Resize = new Resize ( Mode.FIT_TO_PAGE, Position.CENTERED );

pdf.addImageStream(image.data, ColorSpace.DEVICE_RGB, resize);

Then I just save my pdf to a ByteArray and use the FileReference to save it.

var bytes:ByteArray = pdf.save(Method.LOCAL);

var file:FileReference = new FileReference();

file.save(bytes, filename);

Keep in mind that although the panels are high resolution, they are still bitmap graphics. So, you will not be able to copy and paste any of your text out of the resulting PDF.

In order for all this to work, I am using 0.1.5 Beta version of AlivePDF, Flex 3.4 and Flash Player 10.

UPDATE: One last note. Because this is generating a 300DPI version of your component, it takes some time. A few seconds for a few page document.