Tech Blog

Last week I started working on a new version of the print functionality in Floorplanner. The problem with the previous version was that it didn’t print shadows, it was impossible to rotate the plan to landscape and textures didn’t look very well. Overall it produced a very mediocre image compared to the visual quality of a plan on the screen. As can be seen below:

Old print output

For printing we use the AS2 PrintJob class, which works really easy, with a small disadvantage: it doesn’t print Floorplans properly. I tried all kinds of settings for this class, with as input just a MovieClip with a drawing of the plan on it. I tried setting the printAsBitmap to true and false, both giving the exact same result. So although being stuck with it, the printAsBitmap boolean inspired me to investigate the Bitmap thing. We already had an image export utility, which produces images of a Floorplan with the same quality as it is shown in the FlashPlayer. The funny thing is that when I printed this exported image, the print quality was really good, at least a lot better than our own printing functionality. So for some reason, even if I used the printAsBitmap functionality, it still didn’t produce the same quality as using a real bitmap.
Of course we could have stopped here and just tell the users of Floorplanner to print the exported image. But since we are Floorplanner, we didn’t want to introduce another step requiring user action in the printing process, after all, we are the “easiest way” .
So I decided to use the same BitmapData created for the image export as basis for the printing. The first results where rather disappointing, I attached the created BitmapData to a MovieClip which in turn was given to the PrintJob. The produced print was of really low quality, you could easily see pixels all over the place. I tried using more pixels but now I bumped into the pixel limit of BitmapData (2880×2880 pixels). To work around this I invented the BigBitmapData class, this is a wrapper class that mimics the functionality of the BitmapData class, but which doesn’t have an upper limit of the number of pixels which can be used. When an instance of BitBitmapData is created which is bigger than 2880 by 2880, it creates additional BitmapDatas to store the additional pixels needed. So in fact the BigBitmapData internally stores an two dimensional array of BitmapDatas to bypass the pixel limit.
So with this new class I was able to scale up the created image to unprecedented sizes. I did a lot of printing experiments with scaling of the input, I tried scaling settings from 2 times to more than 10 times! This huge bitmap was attached to a MovieClip which in turn had to be scaled to fit on one single page of the printer. These values did give a better result, but still not good enough. It turned out that I had to take the DPI of the printer into account. The optimal scale factor turned out to be (1 / 72) * 300. The 72 is the DPI of the screen, and the 300 is the DPI of the printer. Furthermore a ‘point’ (print unit of measurement) is 1/72 inch, while the size of a pixel (screen unit of measurement) is dependent on the resolution of the screen.
So what this method actually does is creating a big image (which is resized to the paper contents) with enough quality to be printable on a 300 DPI printer.

New print output

So as you can see in the second image above, the new print looks a lot better, and since the new print uses bitmaps it is really easy to rotate it to always produce a print that tries to fill the entire paper.

A disadvantage of this method is that it takes quite some computational power to compute all the pixels for the bitmap that is created in memory, so as a result the FlashPlayer and sometimes even the browser freezes for a moment. Although this isn’t very good, we thought this behavior is acceptable since the quality of the prints is much better than the previous ones and the freeze time is actually really short. If you are not convinced by the images (which is understandable since the quality difference can only be seen on paper), just check it out!